rsh .\} rksh .\} rksh93 .\} [ \(+-abcefhikmnoprstuvxBCD ] [ -R file ] [ \(+-o option ] .\|.\|. [ - ] [ arg .\|.\|. ]

A blank\^ is a tab or a space . An identifier\^ is a sequence of letters, digits, or underscores starting with a letter or underscore. Identifiers are used as components of variable\^ names. A vname\^ is a sequence of one or more identifiers separated by a \s+2.\s-2 and optionally preceded by a \s+2.\s-2. Vnames are used as function and variable names. A word\^ is a sequence of characters\^ from the character set defined by the current locale, excluding non-quoted metacharacters .

A command\^ is a sequence of characters in the syntax of the shell language. The shell reads each command and carries out the desired action either directly or by invoking separate utilities. A built-in command is a command that is carried out by the shell itself without creating a separate process. Some commands are built-in purely for convenience and are not documented here. Built-ins that cause side effects in the shell environment and built-ins that are found before performing a path search (see Execution\^ below) are documented here. For historical reasons, some of these built-ins behave differently than other built-ins and are called "special built-ins" .

A pipeline\^ is a sequence of one or more commands\^ separated by \(bv . The standard output of each command but the last is connected by a pipe (2) to the standard input of the next command. Each command, except possibly the last, is run as a separate process; the shell waits for the last command to terminate. The exit status of a pipeline is the exit status of the last command unless the pipefail option is enabled. Each pipeline can be preceded by the "reserved word" ! which causes the exit status of the pipeline to become 0 if the exit status of the last command is non-zero, and 1 if the exit status of the last command is 0.

A list\^ is a sequence of one or more pipelines separated by ; , & , \(bv& , && , or \(bv\|\(bv , and optionally terminated by ; , & , or \(bv& . Of these five symbols, ; , & , and \(bv& have equal precedence, which is lower than that of && and \(bv\|\(bv . The symbols && and \(bv\|\(bv also have equal precedence. A semicolon ( ; ) causes sequential execution of the preceding pipeline; an ampersand ( & ) causes asynchronous execution of the preceding pipeline (i.e., the shell does not\^ wait for that pipeline to finish). The symbol \(bv& causes asynchronous execution of the preceding pipeline with a two-way pipe established to the parent shell; the standard input and output of the spawned pipeline can be written to and read from by the parent shell by applying the redirection operators <& and >& with arg p to commands and by using -p option of the built-in commands read and print described later. The symbol && (\| \(bv\|\(bv \^) causes the list\^ following it to be executed only if the preceding pipeline returns a zero (non-zero) value. One or more new-lines may appear in a list\^ instead of a semicolon, to delimit a command. The first item \^ of the first pipeline\^ of a list\^ that is a simple command not beginning with a redirection, and not occurring within a while , until , or if list , can be preceded by a semicolon. This semicolon is ignored unless the showme option is enabled as described with the set built-in below.

A command\^ is either a simple-command or one of the following. Unless otherwise stated, the value returned by a command is that of the last simple-command executed in the command.

\f3for \f2vname\^ \*(OK \f3in \f2word\^ .\|.\|. \*(CK \f3;do \f2list\^ \f3;done Each time a for command is executed, vname\^ is set to the next word\^ taken from the in word\^ list. If in " word\^" .\|.\|. is omitted, then the for command executes the \f3do \f2list\^ once for each positional parameter that is set starting from 1 (see "Parameter Expansion\^" below). Execution ends when there are no more words in the list.

\f3for (( \*(OK\f2expr1\^\*(CK \f3; \*(OK\f2expr2\^\*(CK \f3; \*(OK\f2expr3\^\*(CK \f3)) \f3;do \f2list\^ \f3;done The arithmetic expression expr1 is evaluated first (see "Arithmetic evaluation" below). The arithmetic expression expr2 is repeatedly evaluated until it evaluates to zero and when non-zero, list is executed and the arithmetic expression expr3 evaluated. If any expression is omitted, then it behaves as if it evaluated to 1.

\f3select \f2vname\^ \*(OK \f3in \f2word\^ .\|.\|. \*(CK \f3;do \f2list\^ \f3;done A select command prints on standard error (file descriptor 2) the set of word s, each preceded by a number. If in " word\^" .\|.\|. is omitted, then the positional parameters starting from 1 are used instead (see "Parameter Expansion\^" below). The PS3 prompt is printed and a line is read from the standard input. If this line consists of the number of one of the listed word s, then the value of the variable vname\^ is set to the word\^ corresponding to this number. If this line is empty, the selection list is printed again. Otherwise the value of the variable vname\^ is set to null . The contents of the line read from standard input is saved in the variable REPLY . The list\^ is executed for each selection until a break\^ or end-of-file\^ is encountered. If the REPLY variable is set to null\^ by the execution of list , then the selection list is printed before displaying the PS3 prompt for the next selection.

\f3case \f2word\^ \f3in \*(OK \*(OK\f3(\*(CK\f2pattern\^ \*(OK \(bv \f2pattern\^ \*(CK .\|.\|. \f3) \f2list\^ \f3;; \*(CK .\|.\|. \f3esac A case command executes the list\^ associated with the first pattern\^ that matches word . The form of the patterns is the same as that used for file-name generation (see "File Name Generation\^" below). The ;; operator causes execution of case to terminate. If ;& is used in place of ;; the next subsequent list, if any, is executed.

\f3if \f2list\^ \f3;then \f2list\^ \*(OK \ \f3;elif \f2list\^ \f3;then \f2list\^ \*(CK .\|.\|. \ \*(OK \f3;else \f2list\^ \*(CK \f3;fi The list\^ following \f3if is executed and, if it returns a zero exit status, the list\^ following the first then is executed. Otherwise, the list\^ following \f3elif is executed and, if its value is zero, the list\^ following the next then is executed. Failing each successive elif list\^ , the else list\^ is executed. If the if list\^ has non-zero exit status and there is no else list , then the if command returns a zero exit status.

0 \f3while \f2list\^ \f3;do \f2list\^ \f3;done

\f3until \f2list\^ \f3;do \f2list\^ \f3;done

A while command repeatedly executes the while list\^ and, if the exit status of the last command in the list is zero, executes the do list ; otherwise the loop terminates. If no commands in the do list\^ are executed, then the while command returns a zero exit status; until may be used in place of while to negate the loop termination test.

\f3((\f2expression\^\f3))

The expression\^ is evaluated using the rules for arithmetic evaluation described below. If the value of the arithmetic expression is non-zero, the exit status is 0, otherwise the exit status is 1.

\f3(\f2list\^\f3)

Execute list\^ in a separate environment. Note, that if two adjacent open parentheses are needed for nesting, a space must be inserted to avoid evaluation as an arithmetic command as described above.

\f3{ \f2list\^\f3;}

list\^ is simply executed. Note that unlike the metacharacters ( and ) , { and } are "reserved word" s and must occur at the beginning of a line or after a ; in order to be recognized.

\f3[[\f2 expression \^\f3]]

Evaluates expression\^ and returns a zero exit status when expression\^ is true. See "Conditional Expressions\^" below, for a description of expression .

0 \f3function \f2varname\^ \f3{ \f2list\^ \f3;}

\f2varname\^ \f3() { \f2list\^ \f3;}

Define a function which is referenced by varname . A function whose varname\^ contains a \s+2.\s-2 is called a discipline function and the portion of the varname\^ preceding the last \s+2.\s-2 must refer to an existing variable. The body of the function is the list\^ of commands between { and } . A function defined with the \f3function \f2varname\^ syntax can also be used as an argument to the \f3. special built-in command to get the equivalent behavior as if the \f2varname\^\f3() syntax were used to define it. (See Functions\^ below.)

\f3time \*(OK \f2pipeline\^ \*(CK

If \f2pipeline\^ is omitted the user and system time for the current shell and completed child processes is printed on standard error. Otherwise, pipeline\^ is executed and the elapsed time as well as the user and system time are printed on standard error. The TIMEFORMAT variable may be set to a format string that specifies how the timing information should be displayed. See "Shell Variables" below for a description of the TIMEFORMAT variable.

The following reserved words are recognized as reserved only when they are the first word of a command and are not quoted:

0 \f2varname\^\f3=\f2word\^

\f2varname\^\f3[\f2word\^\f3]=\f2word\^

No space is permitted between \f2varname\^ and the \f3= or between \f3= and word\^.

\f2varname\^\f3=(\f2assign_list\^\f3) No space is permitted between \f2varname\^ and the \f3=. An \f2assign_list\^ can be one of the following:

In addition, a \f3+= can be used in place of the \f3= to signify adding to or appending to the previous value. When \f3+= is applied to an arithmetic type, \f2word\^ is evaluated as an arithmetic expression and added to the current value. When applied to a string variable, the value defined by \f2word\^ is appended to the value. For compound assignments, the previous value is not unset and the new values are appended to the current ones provided that the types are compatible.

The right hand side of a variable assignment undergoes all the expansion list below except word splitting, brace expansion, and file name generation. When the left hand side is an assignment is a compound variable and the right hand is the name of a compound variable, the compound variable on the right will be copied or appended to the compound variable on the left.

0 A word beginning with # causes that word and all the following characters up to a new-line to be ignored.

Aliasing\^ is performed when scripts are read, not while they are executed. Therefore, for an alias to take effect, the alias definition command has to be executed before the command which references the alias is read.

The following aliases are compiled into the shell but can be unset or redefined:

In addition, when expanding a "variable assignment" , tilde substitution is attempted when the value of the assignment begins with a \(ap , and when a \(ap appears after a : . The : also terminates a \(ap login name.

cuts fields 1 and 3 from the files file1 and file2 respectively, pastes the results together, and sends it to the processes process1 and process2 , as well as putting it onto the standard output. Note that the file, which is passed as an argument to the command, is a UNIX pipe (2) so programs that expect to lseek (2) on the file will not work.

Process substitution of the form \f3<(\f2list\^\f3) can also be used with the < redirection operator which causes the output of list\^ to be standard input or the input for whatever file descriptor is specified.

The shell supports both indexed and associative arrays. An element of an array variable is referenced by a subscript . A subscript\^ for an indexed array is denoted by an arithmetic expression\^ (see "Arithmetic evaluation" below) between a [ and a ] . To assign values to an indexed array, use \f2vname\f3=(\f2value .\|.\|.\f3) or \f3set -A \f2vname \f2value .\|.\|. . The value of all non-negative subscripts must be in the range of 0 through 4,194,303. A negative subscript is treated as an offset from the maximum current index +1 so that -1 refers to the last element. Indexed arrays can be declared with the -a option to typeset. Indexed arrays need not be declared. Any reference to a variable with a valid subscript is legal and an array will be created if necessary.

An associative array is created with the -A option to typeset. A subscript\^ for an associative array is denoted by a string enclosed between [ and ] .

Referencing any array without a subscript is equivalent to referencing the array with subscript 0.

The value\^ of a variable\^ may be assigned by writing:

0 or

0 A nameref\^ is a variable that is a reference to another variable. A nameref is created with the -n attribute of typeset . The value of the variable at the time of the typeset command becomes the variable that will be referenced whenever the nameref variable is used. The name of a nameref cannot contain a \s+2.\s-2. When a variable or function name contains a \s+2.\s-2, and the portion of the name up to the first \s+2.\s-2 matches the name of a nameref, the variable referred to is obtained by replacing the nameref portion with the name of the variable referenced by the nameref. If a nameref is used as the index of a for loop, a name reference is established for each item in the list. A nameref provides a convenient way to refer to the variable inside a function whose name is passed as an argument to a function. For example, if the name of a variable is passed as the first argument to a function, the command

inside the function causes references and assignments to var to be references and assignments to the variable whose name has been passed to the function.

If any of the floating point attributes, -E , -F , or -X , or the integer attribute, -i , is set for vname , then the value\^ is subject to arithmetic evaluation as described below.

Positional parameters, parameters denoted by a number, may be assigned values with the set\^ special built-in command. Parameter $0 is set from argument zero when the shell is invoked.

The character $ is used to introduce substitutable parameters .

\f3${\f2parameter\^\f3} The shell reads all the characters from ${ to the matching } as part of the same word even if it contains braces or metacharacters. The value, if any, of the parameter is substituted. The braces are required when parameter\^ is followed by a letter, digit, or underscore that is not to be interpreted as part of its name, when the variable name contains a \s+2.\s-2. The braces are also required when a variable is subscripted unless it is part of an Arithmetic Expression or a Conditional Expression. If parameter\^ is one or more digits then it is a positional parameter. A positional parameter of more than one digit must be enclosed in braces. If parameter\^ is \(** or @ , then all the positional parameters, starting with $1 , are substituted (separated by a field separator character). If an array vname\^ with subscript \(** @ , or of the form sub1\^ .. sub2 . is used, then the value for each of the elements between sub1\^ and sub2\^ inclusive (or all elements for \(** and @ ) is substituted, separated by the first character of the value of IFS .

\f3${#\f2parameter\^\f3} If parameter\^ is \(** or @ , the number of positional parameters is substituted. Otherwise, the length of the value of the parameter\^ is substituted.

0 \f3${#\f2vname\f3[*]}

\f3${#\f2vname\f3[@]} The number of elements in the array vname\^ is substituted.

0 \f3${@\f2vname\^\f3} Expands to the type name (See "Type Variables"\^ below) or attributes of the variable referred to by vname .

\f3${!\f2vname\^\f3} Expands to the name of the variable referred to by vname . This will be vname\^ except when vname\^ is a name reference.

\f3${!\f2vname\^\f3[\f2subscript\^\f3]} Expands to name of the subscript unless subscript\^ is * , @ . or of the form sub1\^ .. sub2 . When subscript\^ is * , the list of array subscripts for \f2vname\^ is generated. For a variable that is not an array, the value is 0 if the variable is set. Otherwise it is null. When subscript\^ is @ , same as above, except that when used in double quotes, each array subscript yields a separate argument. When subscript\^ is of the form sub1\^ .. sub2\^ it expands to the list of subscripts between sub1\^ and sub2\^ inclusive using the same quoting rules as @ .

\f3${!\f2prefix\^\f3*} Expands to the names of the variables whose names begin with prefix .

\f3${\f2parameter\^\f3:-\f2word\^\f3} If parameter\^ is set and is non-null then substitute its value; otherwise substitute word .

\f3${\f2parameter\^\f3:=\f2word\^\f3} If parameter\^ is not set or is null then set it to word ; the value of the parameter is then substituted. Positional parameters may not be assigned to in this way.

\f3${\f2parameter\^\f3:?\f2word\^\f3} If parameter\^ is set and is non-null then substitute its value; otherwise, print word\^ and exit from the shell (if not interactive). If word\^ is omitted then a standard message is printed.

\f3${\f2parameter\^\f3:+\f2word\^\f3} If parameter\^ is set and is non-null then substitute word ; otherwise substitute nothing.

In the above, word\^ is not evaluated unless it is to be used as the substituted string, so that, in the following example, pwd is executed only if d is not set or is null:

If the colon ( : ) is omitted from the above expressions, then the shell only checks whether parameter\^ is set or not.

0 \f3${\f2parameter\^\f3:\f2offset\^\f3:\f2length\^\f3}

\f3${\f2parameter\^\f3:\f2offset\^\f3} Expands to the portion of the value of parameter\^ starting at the character (counting from 0\^ ) determined by expanding offset\^ as an arithmetic expression and consisting of the number of characters determined by the arithmetic expression defined by length. In the second form, the remainder of the value is used. If A negative offset\^ counts backwards from the end of parameter . Note that one or more blank s is required in front of a minus sign to prevent the shell from interpreting the operator as :- . If parameter\^ is \(** or @ , or is an array name indexed by \(** or @ , then offset\^ and length\^ refer to the array index and number of elements respectively. A negative offset\^ is taken relative to one greater than the highest subscript for indexed arrays. The order for associate arrays is unspecified.

0 \f3${\f2parameter\^\f3#\f2pattern\^\f3}

\f3${\f2parameter\^\f3##\f2pattern\^\f3}

If the shell pattern\^ matches the beginning of the value of parameter , then the value of this expansion is the value of the parameter\^ with the matched portion deleted; otherwise the value of this parameter\^ is substituted. In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted. When parameter\^ is @ , * , or an array variable with subscript @ or * , the substring operation is applied to each element in turn.

0 \f3${\f2parameter\^\f3%\f2pattern\^\f3}

\f3${\f2parameter\^\f3%%\f2pattern\^\f3}

If the shell pattern\^ matches the end of the value of parameter , then the value of this expansion is the value of the parameter\^ with the matched part deleted; otherwise substitute the value of parameter . In the first form the smallest matching pattern is deleted and in the second form the largest matching pattern is deleted. When parameter\^ is @ , * , or an array variable with subscript @ or * , the substring operation is applied to each element in turn.

0 \f3${\f2parameter\^\f3/\f2pattern\^\f3/\f2string\^\f3}

\f3${\f2parameter\^\f3//\f2pattern\^\f3/\f2string\^\f3}

\f3${\f2parameter\^\f3/#\f2pattern\^\f3/\f2string\^\f3}

\f3${\f2parameter\^\f3/%\f2pattern\^\f3/\f2string\^\f3}

Expands parameter\^ and replaces the longest match of pattern\^ with the given string. Each occurrence of \f3\e\f2n\^ in string is replaced by the portion of \f2parameter\^ that matches the \f2n\^-th sub-pattern. In the first form, only the first occurrence of pattern\^ is replaced. In the second form, each match for pattern\^ is replaced by the given string. The third form restricts the pattern match to the beginning of the string while the fourth form restricts the pattern match to the end of the string. When string\^ is null, the pattern\^ will be deleted and the / in front of string\^ may be omitted. When parameter\^ is @ , * , or an array variable with subscript @ or * , the substitution operation is applied to each element in turn. In this case, the string\^ portion of word\^ will be re-evaluated for each element.

The following parameters are automatically set by the shell:

The following variables are used by the shell:

The shell gives default values to \f3\s-1PATH\s+1, \f3\s-1PS1\s+1, \f3\s-1PS2\s+1, \f3\s-1PS3\s+1, \f3\s-1PS4\s+1, \f3\s-1MAILCHECK\s+1, \f3\s-1FCEDIT\s+1, \f3\s-1TMOUT\s+1 and \f3\s-1IFS\s+1, while HOME , SHELL , ENV , and MAIL are not set at all by the shell (although HOME is\^ set by login (1)). On some systems MAIL and SHELL are also set by login (1).

If the braceexpand ( -B ) option is set then each of the fields resulting from IFS are checked to see if they contain one or more of the brace patterns {*,*} , { l1 .. l2 } , { n1 .. n2 } , { n1 .. n2 % fmt } , { n1 .. n2 .. n3 } , or { n1 .. n2 .. n3 % fmt } , where * represents any character, l1\^ , l2\^ are letters and n1\^ , n2\^ , n3\^ are signed numbers and fmt\^ is a format specified as used by printf . In each case, fields are created by prepending the characters before the { and appending the characters after the } to each of the strings generated by the characters between the { and } . The resulting fields are checked to see if they have any brace patterns.

In the first form, a field is created for each string between { and , , between , and , , and between , and } . The string represented by * can contain embedded matching { and } without quoting. Otherwise, each { and } with * must be quoted.

In the seconds form, l1\^ and l2\^ must both be either upper case or both be lower case characters in the C locale. In this case a field is created for each character from l1\^ thru l2\^ .

In the remaining forms, a field is created for each number starting at n1\^ and continuing until it reaches n2\^ incrementing n1\^ by n3\^ . The cases where n3\^ is not specified behave as if n3\^ where 1 if n1 <= n2 and -1 otherwise. If forms which specify % fmt\^ any format flags, widths and precisions can be specified and fmt\^ can end in any of the specifiers cdiouxX . For example, {a,z}{1..5..3%02d}{b..c}x expands to the 8 fields, a01bx , a01cx , a04bx , a04cx , z01bx , z01cx , z04bx and z4cx .

0

0

When \f2pattern-list\^ is contained within parentheses, the backslash character \f3\e is treated specially even when inside a character class. All ANSI-C character escapes are recognized and match the specified character. In addition the following escape sequences are recognized:

0

A pattern of the form \f3%(\f2pattern-pair\^(s)\f3) is a sub-pattern that can be used to match nested character expressions. Each pattern-pair\^ is a two character sequence which cannot contain & or \(bv . The first pattern-pair\^ specifies the starting and ending characters for the match. Each subsequent pattern-pair\^ represents the beginning and ending characters of a nested group that will be skipped over when counting starting and ending character matches. The behavior is unspecified when the first character of a pattern-pair\^ is alpha-numeric except for the following:

0

Each sub-pattern in a composite pattern is numbered, starting at 1, by the location of the \f3( within the pattern. The sequence \f3\e\f2n\^, where \f2n\^ is a single digit and \f3\e\f2n\^ comes after the \f2n-th. sub-pattern, matches the same string as the sub-pattern itself.

Finally a pattern can contain sub-patterns of the form \f3\(ap(\f2options\^\f3:\f2pattern-list\^\f3), where either \f2options\^ or \f3:\f2pattern-list\^ can be omitted. Unlike the other compound patterns, these sub-patterns are not counted in the numbered sub-patterns. If \f2options\^ is present, it can consist of one or more of the following:

0

0

\e0 Causes the remainder of the string to be ignored.

\eE Equivalent to the escape character (ascii 033 ),

\ee Equivalent to the escape character (ascii 033 ),

\ec x Expands to the character control-\f2x.

\eC[. name .] Expands to the collating element \f2name.

Inside double quote marks (\f3"\^"), parameter and command substitution occur and \e quotes the characters \e , \*` , \f3", and $ . A $ in front of a double quoted string will be ignored in the "C" or "POSIX" locale, and may cause the string to be replaced by a locale specific string otherwise. The meaning of "$\(**" and "$@" is identical when not quoted or when used as a variable assignment value or as a file name. However, when used as a command argument, "$\(**" is equivalent to \f3"$1\f2d\f3\|$2\f2d\|.\|.\|.\f3", where d is the first character of the IFS variable, whereas "$@" is equivalent to "$1"\| "$2"\| .\|.\|.\^. Inside grave quote marks (\f3\*`\^\*`), \e quotes the characters \e , \*` , and $ . If the grave quotes occur within double quotes, then \e also quotes the character \f3".

The special meaning of reserved words or aliases can be removed by quoting any character of the reserved word. The recognition of function names or built-in command names listed below cannot be altered by quoting them.

An arithmetic expression uses the same syntax, precedence, and associativity of expression as the C language. All the C language operators that apply to floating point quantities can be used. In addition, the operator ** can be used for exponentiation. It has higher precedence than multiplication and is left associative. In addition, when the value of an arithmetic variable or sub-expression can be represented as a long integer, all C language integer arithmetic operations can be performed. Variables can be referenced by name within an arithmetic expression without using the parameter expansion syntax. When a variable is referenced, its value is evaluated as an arithmetic expression.

Any of the following math library functions that are in the C math library can be used within an arithmetic expression:

An internal representation of a variable\^ as a double precision floating point can be specified with the \f3-E \*(OK\f2n\^\*(CK, \f3-F \*(OK\f2n\^\*(CK, or \f3-X \*(OK\f2n\^\*(CK option of the typeset special built-in command. The -E option causes the expansion of the value to be represented using scientific notation when it is expanded. The optional option argument n defines the number of significant figures. The -F option causes the expansion to be represented as a floating decimal number when it is expanded. The -X option cause the expansion to be represented using the %a format defined by ISO C-99. The optional option argument n defines the number of places after the decimal (or radix) point in this case.

An internal integer representation of a variable\^ can be specified with the \f3-i \*(OK\f2n\^\*(CK option of the typeset special built-in command. The optional option argument n specifies an arithmetic base to be used when expanding the variable. If you do not specify an arithmetic base, base 10 will be used.

Arithmetic evaluation is performed on the value of each assignment to a variable with the -E , -F , -X , or -i attribute. Assigning a floating point number to a variable whose type is an integer causes the fractional part to be truncated.

0

\f2string True, if string is not null.

\f3-a \f2file Same as \f3-e below. This is obsolete.

\f3-b \f2file True, if file\^ exists and is a block special file.

\f3-c \f2file True, if file\^ exists and is a character special file.

\f3-d \f2file True, if file\^ exists and is a directory.

\f3-e \f2file True, if file\^ exists.

\f3-f \f2file True, if file\^ exists and is an ordinary file.

\f3-g \f2file True, if file\^ exists and it has its setgid bit set.

\f3-k \f2file True, if file\^ exists and it has its sticky bit set.

\f3-n \f2string True, if length of string\^ is non-zero.

\f3-o \f3?\f2option True, if option named option\^ is a valid option name.

\f3-o \f2option True, if option named option\^ is on.

\f3-p \f2file True, if file\^ exists and is a fifo special file or a pipe.

\f3-r \f2file True, if file\^ exists and is readable by current process.

\f3-s \f2file True, if file\^ exists and has size greater than zero.

\f3-t \f2fildes True, if file descriptor number fildes\^ is open and associated with a terminal device.

\f3-u \f2file True, if file\^ exists and it has its setuid bit set.

\f3-w \f2file True, if file\^ exists and is writable by current process.

\f3-x \f2file True, if file\^ exists and is executable by current process. If file\^ exists and is a directory, then true if the current process has permission to search in the directory.

\f3-z \f2string True, if length of string\^ is zero.

\f3-L \f2file True, if file\^ exists and is a symbolic link.

\f3-h \f2file True, if file\^ exists and is a symbolic link.

\f3-N \f2file True, if file\^ exists and the modification time is greater than the last access time.

\f3-O \f2file True, if file\^ exists and is owned by the effective user id of this process.

\f3-G \f2file True, if file\^ exists and its group matches the effective group id of this process.

\f3-S \f2file True, if file\^ exists and is a socket.

\f2file1 \f3-nt \f2file2 True, if file1\^ exists and file2\^ does not, or file1\^ is newer than file2 .

\f2file1 \f3-ot \f2file2 True, if file2\^ exists and file1\^ does not, or file1\^ is older than file2 .

\f2file1 \f3-ef \f2file2 True, if file1\^ and file2\^ exist and refer to the same file.

\f2string \f3== \f2pattern True, if string\^ matches pattern . Any part of pattern\^ can be quoted to cause it to be matched as a string. With a successful match to a pattern, the .sh.match array variable will contain the match and sub-pattern matches.

\f2string \f3= \f2pattern Same as \f3== above, but is obsolete.

\f2string \f3!= \f2pattern True, if string\^ does not match pattern . When the string\^ matches the pattern\^ the .sh.match array variable will contain the match and sub-pattern matches.

\f2string \f3=\(ap \f2ere True if string\^ matches the pattern \(ap(E) ere\^ where ere\^ is an extended regular expression.

\f2string1 \f3< \f2string2 True, if string1\^ comes before string2\^ based on ASCII value of their characters.

\f2string1 \f3> \f2string2 True, if string1\^ comes after string2\^ based on ASCII value of their characters.

The following obsolete arithmetic comparisons are also permitted:

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\f2exp1 \f3-eq \f2exp2 True, if exp1\^ is equal to exp2 .

\f2exp1 \f3-ne \f2exp2 True, if exp1\^ is not equal to exp2 .

\f2exp1 \f3-lt \f2exp2 True, if exp1\^ is less than exp2 .

\f2exp1 \f3-gt \f2exp2 True, if exp1\^ is greater than exp2 .

\f2exp1 \f3-le \f2exp2 True, if exp1\^ is less than or equal to exp2 .

\f2exp1 \f3-ge \f2exp2 True, if exp1\^ is greater than or equal to exp2 .

In each of the above expressions, if file\^ is of the form \f3/dev/fd/\f2n, where n\^ is an integer, then the test is applied to the open file whose descriptor number is n .

A compound expression can be constructed from these primitives by using any of the following, listed in decreasing order of precedence.

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\f3(\f2expression\f3) True, if expression\^ is true. Used to group expressions.

\f3! \f2expression True if expression\^ is false.

\f2expression1 \f3&& \f2expression2 True, if expression1\^ and expression2\^ are both true.

\f2expression1 \f3\(bv\(bv \f2expression2 True, if either expression1\^ or expression2\^ is true.

In each of the following redirections, if file\^ is of the form \f3/dev/sctp/\f2host\f3/\f2port, \f3/dev/tcp/\f2host\f3/\f2port, or \f3/dev/udp/\f2host\f3/\f2port, where host\^ is a hostname or host address, and port\^ is a service given by name or an integer port number, then the redirection attempts to make a \f3tcp, \f3sctp or \f3udp connection to the corresponding socket.

No intervening space is allowed between the characters of redirection operators.

14 < word Use file word\^ as standard input (file descriptor 0).

> word Use file word\^ as standard output (file descriptor 1). If the file does not exist then it is created. If the file exists, and the noclobber option is on, this causes an error; otherwise, it is truncated to zero length.

>| word Sames as > , except that it overrides the noclobber option.

>; word Write output to a temporary file. If the command completes successfully rename it to word , otherwise, delete the temporary file. >; word cannot be used with the exec (2). built-in.

>> word Use file word\^ as standard output. If the file exists, then output is appended to it (by first seeking to the end-of-file); otherwise, the file is created.

<> word Open file word\^ for reading and writing as standard output.

<>; word The same as <> word except that if the command completes successfully, word\^ is truncated to the offset at command completion. <>; word cannot be used with the exec (2). built-in.

\f3<<\*(OK\f3-\*(CK\f2word The shell input is read up to a line that is the same as word after any quoting has been removed, or to an end-of-file. No parameter substitution, command substitution, arithmetic substitution or file name generation is performed on word . The resulting document, called a here-document , becomes the standard input. If any character of word\^ is quoted, then no interpretation is placed upon the characters of the document; otherwise, parameter expansion, command substitution, and arithmetic substitution occur, \enew-line is ignored, and \e must be used to quote the characters \e , $ , \*` . If - is appended to << , then all leading tabs are stripped from word\^ and from the document. If # is appended to << , then leading spaces and tabs will be stripped off the first line of the document and up to an equivalent indentation will be stripped from the remaining lines and from word . A tab stop is assumed to occur at every 8 columns for the purposes of determining the indentation.

\f3<<<\f2word A short form of here document in which \f2word becomes the contents of the here-document after any parameter expansion, command substitution, and arithmetic substitution occur.

<& digit The standard input is duplicated from file descriptor digit (see dup (2)). Similarly for the standard output using \f3>&\^\f2digit.

<& digit - The file descriptor given by digit is moved to standard input. Similarly for the standard output using \f3>&\^\f2digit\f3-.

<&- The standard input is closed. Similarly for the standard output using >&- .

<&p The input from the co-process is moved to standard input.

>&p The output to the co-process is moved to standard output.

<# \^\^\^ (( expr )) Evaluate arithmetic expression expr\^ and position file descriptor 0 to the resulting value bytes from the start of the file. The variables CUR and EOF evaluate to the current offset and end-of-file offset respectively when evaluating expr.

># \^\^\^ (( offset )) The same as <# except applies to file descriptor 1.

<# pattern Seeks forward to the beginning of the next line containing pattern .

<## pattern The same as <# except that the portion of the file that is skipped is copied to standard output.

If one of the above is preceded by a digit, with no intervening space, then the file descriptor number referred to is that specified by the digit (instead of the default 0 or 1). If one of the above, other than >&- and the ># and <# forms, is preceded by { varname } with no intervening space, then a file descriptor number > 10 will be selected by the shell and stored in the variable varname . If >&- or the any of the ># and <# forms is preceded by { varname } the value of varname\^ defines the file descriptor to close or position. For example:

means file descriptor 2 is to be opened for writing as a duplicate of file descriptor 1 and

means open file named file for reading and store the file descriptor number in variable n .

The order in which redirections are specified is significant. The shell evaluates each redirection in terms of the ( "file descriptor" ", " file ) association at the time of evaluation. For example:

first associates file descriptor 1 with file fname\^ . It then associates file descriptor 2 with the file associated with file descriptor 1 (i.e. fname\^ ). If the order of redirections were reversed, file descriptor 2 would be associated with the terminal (assuming file descriptor 1 had been) and then file descriptor 1 would be associated with file fname\^ .

If a command is followed by & and job control is not active, then the default standard input for the command is the empty file /dev/null . Otherwise, the environment for the execution of a command contains the file descriptors of the invoking shell as modified by input/output specifications.

The environment for any simple-command\^ or function may be augmented by prefixing it with one or more variable assignments. A variable assignment argument is a word of the form identifier=value . Thus:

are equivalent (as far as the above execution of cmd\^ is concerned except for special built-in commands listed below - those that are preceded with a dagger).

If the obsolete -k option is set, all\^ variable assignment arguments are placed in the environment, even if they occur after the command name. The following first prints "a=b c" and then c :

echo \|a=b \|c
set \|-k
echo \|a=b \|c

For historical reasons, there are two ways to define functions, the name (\^) syntax and the function name\^ syntax, described in the Commands section above. Shell functions are read in and stored internally. Alias names are resolved when the function is read. Functions are executed like commands with the arguments passed as positional parameters. (See Execution below.)

Functions defined by the function name syntax and called by name execute in the same process as the caller and share all files and present working directory with the caller. Traps caught by the caller are reset to their default action inside the function. A trap condition that is not caught or ignored by the function causes the function to terminate and the condition to be passed on to the caller. A trap on EXIT set inside a function is executed in the environment of the caller after the function completes. Ordinarily, variables are shared between the calling program and the function. However, the typeset special built-in command used within a function defines local variables whose scope includes the current function. They can be passed to functions that they call in the variable assignment list that precedes the call or as arguments passed as name references. Errors within functions return control to the caller.

Functions defined with the name (\^) syntax and functions defined with the function name syntax that are invoked with the \f3\s+2.\s-2 special built-in are executed in the caller's environment and share all variables and traps with the caller. Errors within these function executions cause the script that contains them to abort.

The special built-in command return is used to return from function calls.

Function names can be listed with the -f or +f option of the typeset special built-in command. The text of functions, when available, will also be listed with -f . Functions can be undefined with the -f option of the unset special built-in command.

Ordinarily, functions are unset when the shell executes a shell script. Functions that need to be defined across separate invocations of the shell should be placed in a directory and the FPATH variable should contain the name of this directory. They may also be specified in the ENV file.

The variable .sh.name contains the name of the variable for which the discipline function is called, .sh.subscript is the subscript of the variable, and .sh.value will contain the value being assigned inside the set discipline function. The variable _ is a reference to the variable including the subscript if any. For the \f3set discipline, changing .sh.value will change the value that gets assigned. Finally, the expansion \f3${\f2var\^\f3.\f2name\^\f3}, when \f2name\^ is the name of a discipline, and there is no variable of this name, is equivalent to the command substitution \f3${ \f2var\^\f3.\f2name\^\f3;}.

When a type is defined a special built-in command of that name is added. These built-ins are declaration commands and follow the same expansion rules as all the special built-in commands defined below that are preceded by \(dg\(dg. These commands can subsequently be used inside further type definitions. The man page for these commands can be generated by using the --man option or any of the other -- options described with getopts . The -r , -a , -A , -h , and -S options of typeset are permitted with each of these new built-ins.

An instance of a type is created by invoking the type name followed by one or more instance names. Each instance of the type is initialized with a copy of the sub-variables except for sub-variables that are defined with the -S option. Variables defined with the -S are shared by all instances of the type. Each instance can change the value of any sub-variable and can also define new discipline functions of the same names as those defined by the type definition as well as any standard discipline names. No additional sub-variables can be defined for any instance.

When defining a type, if the value of a sub-variable is not set and the -r attribute is specified, it causes the sub-variable to be a required sub-variable. Whenever an instance of a type is created, all required sub-variables must be specified. These sub-variables become readonly in each instance.

When unset is invoked on a sub-variable within a type, and the -r attribute has not been specified for this field, the value is reset to the default value associative with the type. Invoking unset on a type instance not contained within another type deletes all sub-variables and the variable itself.

A type definition can be derived from another type definition by defining the first sub-variable name as _ and defining its type as the base type. Any remaining definitions will be additions and modifications that apply to the new type. If the new type name is the same is that of the base type, the type will be replaced and the original type will no longer be accessible.

If the monitor option of the set command is turned on, an interactive shell associates a job with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with & , the shell prints a line which looks like:

[1] 1234

indicating that the job which was started asynchronously was job number 1 and had one (top-level) process, whose process id was 1234.

This paragraph and the next require features that are not in all versions of UNIX and may not apply. If you are running a job and wish to do something else you may hit the key ^Z (control-Z) which sends a STOP signal to the current job. The shell will then normally indicate that the job has been `Stopped', and print another prompt. You can then manipulate the state of this job, putting it in the background with the bg command, or run some other commands and then eventually bring the job back into the foreground with the foreground command fg . A ^Z takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed.

A job being run in the background will stop if it tries to read from the terminal. Background jobs are normally allowed to produce output, but this can be disabled by giving the command "stty tostop" . If you set this tty option, then background jobs will stop when they try to produce output like they do when they try to read input.

There are several ways to refer to jobs in the shell. A job can be referred to by the process id of any process of the job or by one of the following:

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% number The job with the given number.

% string Any job whose command line begins with string .

%? string Any job whose command line contains string .

%% Current job.

%+ Equivalent to %% .

%- Previous job.

The shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work. The notify option of the set command causes the shell to print these job change messages as soon as they occur.

When the monitor option is on, each background job that completes triggers any trap set for CHLD .

When you try to leave the shell while jobs are running or stopped, you will be warned that `You have stopped(running) jobs.' You may use the jobs command to see what they are. If you immediately try to exit again, the shell will not warn you a second time, and the stopped jobs will be terminated. When a login shell receives a HUP signal, it sends a HUP signal to each job that has not been disowned with the disown built-in command described below.

The shell variable PATH defines the search path for the directory containing the command. Alternative directory names are separated by a colon ( : ). The default path is /bin:/usr/bin: (specifying /bin , /usr/bin , and the current directory in that order). The current directory can be specified by two or more adjacent colons, or by a colon at the beginning or end of the path list. If the command name contains a \f3/, then the search path is not used. Otherwise, each directory in the path is searched for an executable file of the given name that is not a directory. If found, and if the shell determines that there is a built-in version of a command corresponding to a given pathname, this built-in is invoked in the current process. If found, and this directory is also contained in the value of the FPATH variable, then this file is loaded into the current shell environment as if it were the argument to the . command except that only preset aliases are expanded, and a function of the given name is executed as described above. If not found, and the file .paths is found, and this file contains a line of the form FPATH= path where path\^ names an existing directory, and this directory contains a file of the given name, then this file is loaded into the current shell environment as if it were the argument to the . special built-in command and a function of the given name is executed. Otherwise, if found, a process is created and an attempt is made to execute the command via exec (2).

When an executable is found, the directory where it is found in is searched for a file named .paths . If this file is found and it contains a line of the form BUILTIN_LIB= value\^ , then the library named by value\^ will be searched for as if it were an option argument to "builtin -f" , and if it contains a built-in of the specified name this will be executed instead of a command by this name. Otherwise, if this file is found and it contains a line of the form name\^ = value\^ in the first or second line, then the environment variable name\^ is modified by prepending the directory specified by value\^ to the directory list. If value\^ is not an absolute directory, then it specifies a directory relative to the directory that the executable was found. If the environment variable name\^ does not already exist it will be added to the environment list for the specified command.

If the file has execute permission but is not an a.out file, it is assumed to be a file containing shell commands. A separate shell is spawned to read it. All non-exported variables are removed in this case. If the shell command file doesn't have read permission, or if the setuid and/or setgid bits are set on the file, then the shell executes an agent whose job it is to set up the permissions and execute the shell with the shell command file passed down as an open file. A parenthesized command is executed in a sub-shell without removing non-exported variables.

The editing features require that the user's terminal accept `RETURN' as carriage return without line feed and that a space (` ') must overwrite the current character on the screen.

Unless the multiline option is on, the editing modes implement a concept where the user is looking through a window at the current line. The window width is the value of COLUMNS if it is defined, otherwise 80. If the window width is too small to display the prompt and leave at least 8 columns to enter input, the prompt is truncated from the left. If the line is longer than the window width minus two, a mark is displayed at the end of the window to notify the user. As the cursor moves and reaches the window boundaries the window will be centered about the cursor. The mark is a > " (<" , * ) if the line extends on the right (left, both) side(s) of the window.

The search commands in each edit mode provide access to the history file. Only strings are matched, not patterns, although a leading ^ in the string restricts the match to begin at the first character in the line.

Each of the edit modes has an operation to list the files or commands that match a partially entered word. When applied to the first word on the line, or the first word after a ; , \(bv , & , or ( , and the word does not begin with \(ap or contain a / , the list of aliases, functions, and executable commands defined by the PATH variable that could match the partial word is displayed. Otherwise, the list of files that match the given word is displayed. If the partially entered word does not contain any file expansion characters, a * is appended before generating these lists. After displaying the generated list, the input line is redrawn. These operations are called command name listing and file name listing, respectively. There are additional operations, referred to as command name completion and file name completion, which compute the list of matching commands or files, but instead of printing the list, replace the current word with a complete or partial match. For file name completion, if the match is unique, a / is appended if the file is a directory and a space is appended if the file is not a directory. Otherwise, the longest common prefix for all the matching files replaces the word. For command name completion, only the portion of the file names after the last / are used to find the longest command prefix. If only a single name matches this prefix, then the word is replaced with the command name followed by a space. When using a tab\^ for completion that does not yield a unique match, a subsequent tab\^ will provide a numbered list of matching alternatives. A specific selection can be made by entering the selection number followed by a tab .

The variable .sh.edcol is set to the input column number of the cursor at the time of the input. The variable .sh.edmode is set to ESC when in vi insert mode (see below) and is null otherwise. By prepending ${.sh.editmode} to a value assigned to .sh.edchar it will cause the shell to change to control mode if it is not already in this mode.

This trap is not invoked for characters entered as arguments to editing directives, or while reading input for a character search.

The notation for escape sequences is M- followed by a character. For example, M-f (pronounced Meta f) is entered by depressing ESC (ascii 033 ) followed by `f'. ( M-F would be the notation for ESC followed by `SHIFT' (capital) `F'.)

All edit commands operate from any place on the line (not just at the beginning). Neither the `RETURN' nor the `LINE FEED' key is entered after edit commands except when noted.

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10 ^F Move cursor forward (right) one character.

10 M-[C Move cursor forward (right) one character.

10 M-f Move cursor forward one word. (The emacs editor's idea of a word is a string of characters consisting of only letters, digits and underscores.)

10 ^B Move cursor backward (left) one character.

10 M-[D Move cursor backward (left) one character.

10 M-b Move cursor backward one word.

10 ^A Move cursor to start of line.

10 M-[H Move cursor to start of line.

10 ^E Move cursor to end of line.

10 M-[Y Move cursor to end of line.

10 ^] char Move cursor forward to character char on current line.

10 M-^] char Move cursor backward to character char on current line.

10 ^X^X Interchange the cursor and mark.

10 erase (User defined erase character as defined by the stty (1) command, usually ^H or # .) Delete previous character.

10 lnext (User defined literal next character as defined by the stty (1) command, or ^V if not defined.) Removes the next character's editing features (if any).

10 ^D Delete current character.

10 M-d Delete current word.

10 M-^H (Meta-backspace) Delete previous word.

10 M-h Delete previous word.

10 M-^? (Meta-DEL) Delete previous word (if your interrupt character is ^? (DEL, the default) then this command will not work).

10 ^T Transpose current character with previous character and advance the cursor in emacs mode. Transpose two previous characters in gmacs mode.

10 ^C Capitalize current character.

10 M-c Capitalize current word.

10 M-l Change the current word to lower case.

10 ^K Delete from the cursor to the end of the line. If preceded by a numerical parameter whose value is less than the current cursor position, then delete from given position up to the cursor. If preceded by a numerical parameter whose value is greater than the current cursor position, then delete from cursor up to given cursor position.

10 ^W Kill from the cursor to the mark.

10 M-p Push the region from the cursor to the mark on the stack.

10 kill (User defined kill character as defined by the stty command, usually ^G or @ .) Kill the entire current line. If two kill characters are entered in succession, all kill characters from then on cause a line feed (useful when using paper terminals).

10 ^Y Restore last item removed from line. (Yank item back to the line.)

10 ^L Line feed and print current line.

10 M-^L Clear the screen.

10 ^@ (Null character) Set mark.

10 M- space (Meta space) Set mark.

10 ^J (New line) Execute the current line.

10 ^M (Return) Execute the current line.

10 eof End-of-file character, normally ^D , is processed as an End-of-file only if the current line is null.

10 ^P Fetch previous command. Each time ^P is entered the previous command back in time is accessed. Moves back one line when not on the first line of a multi-line command.

10 M-[A If the cursor is at the end of the line, it is equivalent to ^R with string\^ set to the contents of the current line. Otherwise, it is equivalent to ^P.

10 M-< Fetch the least recent (oldest) history line.

10 M-> Fetch the most recent (youngest) history line.

10 ^N Fetch next command line. Each time ^N is entered the next command line forward in time is accessed.

10 M-[B Equivalent to ^N.

10 ^R string Reverse search history for a previous command line containing string . If a parameter of zero is given, the search is forward. String is terminated by a `RETURN' or `NEW LINE'. If string is preceded by a ^ , the matched line must begin with string . If string is omitted, then the next command line containing the most recent string is accessed. In this case a parameter of zero reverses the direction of the search.

10 ^O Operate - Execute the current line and fetch the next line relative to current line from the history file.

10 M- digits (Escape) Define numeric parameter, the digits are taken as a parameter to the next command. The commands that accept a parameter are ^F , ^B , erase , ^C , ^D , ^K , ^R , ^P , ^N , ^] , M-. , M-^] , M-_ , M-= , M-b , M-c , M-d , M-f , M-h , M-l and M-^H .

10 M- letter Soft-key - Your alias list is searched for an alias by the name _ letter and if an alias of this name is defined, its value will be inserted on the input queue. The letter must not be one of the above meta-functions.

10 M-[ letter Soft-key - Your alias list is searched for an alias by the name __ letter and if an alias of this name is defined, its value will be inserted on the input queue. This can be used to program function keys on many terminals.

10 M-. The last word of the previous command is inserted on the line. If preceded by a numeric parameter, the value of this parameter determines which word to insert rather than the last word.

10 M-_ Same as M-. .

10 M-* Attempt file name generation on the current word. An asterisk is appended if the word doesn't match any file or contain any special pattern characters.

10 M-ESC Command or file name completion as described above.

10 ^I " tab" Attempts command or file name completion as described above. If a partial completion occurs, repeating this will behave as if M-= were entered. If no match is found or entered after space\^ , a tab\^ is inserted.

10 M-= If not preceded by a numeric parameter, it generates the list of matching commands or file names as described above. Otherwise, the word under the cursor is replaced by the item corresponding to the value of the numeric parameter from the most recently generated command or file list. If the cursor is not on a word, it is inserted instead.

10 ^U Multiply parameter of next command by 4.

10 \e Escape next character. Editing characters, the user's erase, kill and interrupt (normally ^? ) characters may be entered in a command line or in a search string if preceded by a \e . The \e removes the next character's editing features (if any).

10 M-^V Display version of the shell.

10 M-# If the line does not begin with a # , a # is inserted at the beginning of the line and after each new-line, and the line is entered. This causes a comment to be inserted in the history file. If the line begins with a # , the # is deleted and one # after each new-line is also deleted.

When in vi mode on most systems, canonical processing is initially enabled and the command will be echoed again if the speed is 1200 baud or greater and it contains any control characters or less than one second has elapsed since the prompt was printed. The ESC character terminates canonical processing for the remainder of the command and the user can then modify the command line. This scheme has the advantages of canonical processing with the type-ahead echoing of raw mode.

If the option viraw is also set, the terminal will always have canonical processing disabled. This mode is implicit for systems that do not support two alternate end of line delimiters, and may be helpful for certain terminals.

0

1. Variable assignment lists preceding the command remain in effect when the command completes.

2. I/O redirections are processed after variable assignments.

3. Errors cause a script that contains them to abort.

4. They are not valid function names.

5. Words following a command preceded by \(dg\(dg that are in the format of a variable assignment are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and field splitting and file name generation are not performed. These are called declaration\^ built-ins.

\(dg \f3: \*(OK \f2arg\^ .\|.\|. \*(CK The command only expands parameters.

\(dg \f3\|. \f2name\^ \*(OK \f2arg\^ .\|.\|. \*(CK If name\^ is a function defined with the function name\^ reserved word syntax, the function is executed in the current environment (as if it had been defined with the name () syntax.) Otherwise if name\^ refers to a file, the file is read in its entirety and the commands are executed in the current shell environment. The search path specified by PATH is used to find the directory containing the file. If any arguments arg\^ are given, they become the positional parameters while processing the . command and the original positional parameters are restored upon completion. Otherwise the positional parameters are unchanged. The exit status is the exit status of the last command executed.

\(dg\(dg \f3alias \*(OK \f3-ptx \*(CK \*(OK \f2name\*(OK \f3=\f2value\^ \*(CK \*(CK .\|.\|. alias\^ with no arguments prints the list of aliases in the form name=value\^ on standard output. The -p option causes the word alias to be inserted before each one. When one or more arguments are given, an alias\^ is defined for each name\^ whose value\^ is given. A trailing space in value\^ causes the next word to be checked for alias substitution. The obsolete -t option is used to set and list tracked aliases. The value of a tracked alias is the full pathname corresponding to the given name . The value becomes undefined when the value of PATH is reset but the alias remains tracked. Without the -t option, for each name\^ in the argument list for which no value\^ is given, the name and value of the alias is printed. The obsolete -x option has no effect. The exit status is non-zero if a name\^ is given, but no value, and no alias has been defined for the name\^ .

\f3bg \*(OK \f2job\^.\|.\|. \*(CK This command is only on systems that support job control. Puts each specified job\^ into the background. The current job is put in the background if job\^ is not specified. See Jobs for a description of the format of job .

\(dg \f3break \*(OK \f2n\^ \*(CK Exit from the enclosing for\^ , while\^ , until\^ , or select\^ loop, if any. If n\^ is specified, then break n\^ levels.

\f3builtin \*(OK \f3-ds \*(CK \*(OK \f3-f \f2file\^ \*(CK \*(OK \f2name\^ .\|.\|. \*(CK If name\^ is not specified, and no -f option is specified, the built-ins are printed on standard output. The -s option prints only the special built-ins. Otherwise, each name\^ represents the pathname whose basename is the name of the built-in. The entry point function name is determined by prepending b_ to the built-in name. The ISO C/C++ prototype is \f3b_\f2mycommand\f3(int \f2argc, \f3char *\f2argv\f3[], \f3void *\f2context\f3) for the builtin command mycommand\^ where argv\^ is array an of argc\^ elements and context is an optional pointer to a Shell_t structure as described in <ast/shell.h> . Special built-ins cannot be bound to a pathname or deleted. The -d option deletes each of the given built-ins. On systems that support dynamic loading, the -f option names a shared library containing the code for built-ins. The shared library prefix and/or suffix, which depend on the system, can be omitted. Once a library is loaded, its symbols become available for subsequent invocations of builtin . Multiple libraries can be specified with separate invocations of the builtin command. Libraries are searched in the reverse order in which they are specified. When a library is loaded, it looks for a function in the library whose name is lib_init() and invokes this function with an argument of 0 .

0 \f3cd \*(OK \f3-LP \*(CK \*(OK \f2arg\^ \*(CK

\f3cd \*(OK \f3-LP \*(CK \f2old\^ \f2new\^

This command can be in either of two forms. In the first form it changes the current directory to arg . If arg\^ is - the directory is changed to the previous directory. The shell variable HOME is the default arg . The variable PWD is set to the current directory. The shell variable CDPATH defines the search path for the directory containing arg . Alternative directory names are separated by a colon ( : ). The default path is <null> (specifying the current directory). Note that the current directory is specified by a null path name, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If arg begins with a \f3/ then the search path is not used. Otherwise, each directory in the path is searched for arg . The second form of cd substitutes the string new for the string old in the current directory name, PWD , and tries to change to this new directory. By default, symbolic link names are treated literally when finding the directory name. This is equivalent to the -L option. The -P option causes symbolic links to be resolved when determining the directory. The last instance of -L or -P on the command line determines which method is used. The cd\^ command may not be executed by

\f3command \*(OK \f3-pvxV \*(CK \f2name\^ \*(OK \f2arg\^ .\|.\|. \*(CK Without the -v or -V options, command executes name\^ with the arguments given by arg . The -p option causes a default path to be searched rather than the one defined by the value of PATH . Functions will not be searched for when finding name . In addition, if name\^ refers to a special built-in, none of the special properties associated with the leading daggers will be honored. (For example, the predefined alias "redirect=\(fmcommand exec\(fm" prevents a script from terminating when an invalid redirection is given.) With the -x option, if command execution would result in a failure because there are too many arguments, errno E2BIG , the shell will invoke command name\^ multiple times with a subset of the arguments on each invocation. Arguments that occur prior to the first word that expands to multiple arguments and after the last word that expands to multiple arguments will be passed on each invocation. The exit status will be the maximum invocation exit status. With the -v option, command is equivalent to the built-in whence command described below. The -V option causes command to act like "whence -v" .

\(dg \f3continue \*(OK \f2n\^ \*(CK Resume the next iteration of the enclosing for\^ , while\^ , until\^ , or select\^ loop. If n\^ is specified, then resume at the n -th enclosing loop.

\f3disown \*(OK \f2job\^.\|.\|. \*(CK Causes the shell not to send a HUP signal to each given job , or all active jobs if job is omitted, when a login shell terminates.

\f3echo \*(OK \f2arg\^ .\|.\|. \*(CK When the first arg\^ does not begin with a -, and none of the arguments contain a \e, then echo prints each of its arguments separated by a space and terminated by a new-line. Otherwise, the behavior of echo is system dependent and print or printf described below should be used. See echo (1) for usage and description.

\(dg\(dg \f3enum \*(OK \f3-i \*(CK \f2type\^\*(OK=(\f2value\^ .\|.\|.) \*(CK Creates a declaration command named \f2type\^ that is an integer type that allows one of the specified \f2values as enumeration names. If \f3=(\f2value\^ .\|.\|.\|\f3) is omitted, then \f2type\^ must be an indexed array variable with at least two elements and the values are taken from this array variable. If -i is specified the values are case insensitive.

\(dg \f3eval \*(OK \f2arg\^ .\|.\|. \*(CK The arguments are read as input to the shell and the resulting command(s) executed.

\(dg \f3exec \*(OK \f3-c \*(CK \*(OK \f3-a \f2name\^ \*(CK \*(OK \f2arg\^ .\|.\|. \*(CK If arg\^ is given, the command specified by the arguments is executed in place of this shell without creating a new process. The -c option causes the environment to be cleared before applying variable assignments associated with the exec invocation. The -a option causes name\^ rather than the first arg , to become argv[0] for the new process. Input/output arguments may appear and affect the current process. If arg\^ is not given, the effect of this command is to modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when invoking another program.

\(dg \f3exit \*(OK \f2n\^ \*(CK Causes the shell to exit with the exit status specified by n . The value will be the least significant 8 bits of the specified status. If n\^ is omitted, then the exit status is that of the last command executed. An end-of-file will also cause the shell to exit except for a shell which has the ignoreeof option (see set below) turned on.

\(dg\(dg \f3export \*(OK \f3-p \*(CK \*(OK \f2name\^\*(OK\f3=\f2value\^\*(CK \*(CK .\|.\|. If name\^ is not given, the names and values of each variable with the export attribute are printed with the values quoted in a manner that allows them to be re-input. The -p option causes the word export to be inserted before each one. Otherwise, the given name s are marked for automatic export to the environment\^ of subsequently-executed commands.

\f3false Does nothing, and exits 1. Used with until for infinite loops.

\f3fg \*(OK \f2job\^.\|.\|. \*(CK This command is only on systems that support job control. Each job\^ specified is brought to the foreground and waited for in the specified order. Otherwise, the current job is brought into the foreground. See Jobs for a description of the format of job .

\f3getconf \*(OK \f2name\^ \*(OK \f2pathname\^ \*(CK \*(CK Prints the current value of the configuration parameter given by name . The configuration parameters are defined by the IEEE POSIX 1003.1 and IEEE POSIX 1003.2 standards. (See pathconf (2) and sysconf (2).) The pathname argument is required for parameters whose value depends on the location in the file system. If no arguments are given, getconf prints the names and values of the current configuration parameters. The pathname / is used for each of the parameters that requires pathname .

\f3getopts \*(OK \f3 -a \f2name\^ \*(CK \f2optstring vname\^ \*(OK \f2arg\^ .\|.\|. \*(CK Checks arg for legal options. If arg is omitted, the positional parameters are used. An option argument begins with a + or a - . An option not beginning with + or - or the argument -\|- ends the options. Options beginning with + are only recognized when optstring\^ begins with a + . optstring\^ contains the letters that getopts recognizes. If a letter is followed by a : , that option is expected to have an argument. The options can be separated from the argument by blanks. The option -? causes getopts to generate a usage message on standard error. The -a argument can be used to specify the name to use for the usage message, which defaults to $0 . getopts places the next option letter it finds inside variable vname\^ each time it is invoked. The option letter will be prepended with a + when arg begins with a + . The index of the next arg is stored in OPTIND . The option argument, if any, gets stored in OPTARG . A leading : in optstring causes getopts to store the letter of an invalid option in OPTARG , and to set vname to ? for an unknown option and to : when a required option argument is missing. Otherwise, getopts prints an error message. The exit status is non-zero when there are no more options. There is no way to specify any of the options : , + , - , ? , [ , and ] . The option # can only be specified as the first option.

0 \f3hist \*(OK \f3-e \f2ename\^ \*(CK \*(OK \f3-nlr\^ \*(CK \*(OK \f2first\^ \*(OK \f2last\^ \*(CK \*(CK

\f3hist -s \*(OK \f2old\f3\=\f2new\^ \*(CK \*(OK \f2command\^ \*(CK

In the first form, a range of commands from first\^ to last\^ is selected from the last HISTSIZE commands that were typed at the terminal. The arguments first\^ and last\^ may be specified as a number or as a string. A string is used to locate the most recent command starting with the given string. A negative number is used as an offset to the current command number. If the -l option is selected, the commands are listed on standard output. Otherwise, the editor program ename\^ is invoked on a file containing these keyboard commands. If ename\^ is not supplied, then the value of the variable HISTEDIT is used. If HISTEDIT is not set, then FCEDIT (default /bin/ed\^ ) is used as the editor. When editing is complete, the edited command(s) is executed if the changes have been saved. If last\^ is not specified, then it will be set to first . If first\^ is not specified, the default is the previous command for editing and -16 for listing. The option -r reverses the order of the commands and the option -n suppresses command numbers when listing. In the second form, command\^ is interpreted as first\^ described above and defaults to the last command executed. The resulting command is executed after the optional substitution \f2old\^\f3=\f2new\^ is performed.

\f3jobs \*(OK \f3-lnp\^ \*(CK \*(OK \f2job\^ \.\|.\|. \*(CK Lists information about each given job; or all active jobs if job is omitted. The -l option lists process ids in addition to the normal information. The -n option only displays jobs that have stopped or exited since last notified. The -p option causes only the process group to be listed. See Jobs for a description of the format of job .

0 \f3kill \*(OK \f3-s \f2signame\^ \*(CK \f2job\^ .\|.\|.

0 \f3kill \*(OK \f3-n \f2signum\^ \*(CK \f2job\^ .\|.\|.

\f3kill \f3-l \*(OK \f2sig\^ .\|.\|. \*(CK

Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number with the -n option or by name with the -s option (as given in <signal.h> , stripped of the prefix ``SIG'' with the exception that SIGCLD is named CHLD). For backward compatibility, the n and s can be omitted and the number or name placed immediately after the - . If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process will be sent a CONT (continue) signal if it is stopped. The argument job\^ can be the process id of a process that is not a member of one of the active jobs. See Jobs for a description of the format of job . In the third form, "kill -l" , if sig\^ is not specified, the signal names are listed. Otherwise, for each sig\^ that is a name, the corresponding signal number is listed. For each sig\^ that is a number, the signal name corresponding to the least significant 8 bits of sig\^ is listed.

\f3let \f2arg\^ .\|.\|. Each arg is a separate "arithmetic expression" to be evaluated. See "Arithmetic Evaluation" above, for a description of arithmetic expression evaluation. The exit status is 0 if the value of the last expression is non-zero, and 1 otherwise.

\(dg \f3newgrp \*(OK \f2arg\^ .\|.\|. \*(CK Equivalent to "exec /bin/newgrp" " arg\^" .\|.\|.\^.

\f3print \*(OK \f3-CRenprsv\^ \*(CK \*(OK \f3-u \f2unit\^\*(CK \*(OK \f3-f \f2format\^ \*(CK \*(OK \f2arg\^ .\|.\|. \*(CK With no options or with option - or -\|- , each arg is printed on standard output. The -f option causes the arguments to be printed as described by printf . In this case, any e , n , r , R options are ignored. Otherwise, unless the -C , -R , -r , or -v are specified, the following escape conventions will be applied:

\f3printf \f2format\^ \*(OK \f2arg\^ .\|.\|. \*(CK The arguments arg\^ are printed on standard output in accordance with the ANSI-C formatting rules associated with the format string format . If the number of arguments exceeds the number of format specifications, the format\^ string is reused to format remaining arguments. The following extensions can also be used:

\f3pwd \*(OK \f3-LP \*(CK Outputs the value of the current working directory. The -L option is the default; it prints the logical name of the current directory. If the -P option is given, all symbolic links are resolved from the name. The last instance of -L or -P on the command line determines which method is used.

\f3read \*(OK \f3-ACprsv\^ \*(CK \*(OK \f3-d \f2delim\^\*(CK \*(OK \f3-n \f2n\^\*(CK \*(OK \*(OK \f3-N \f2n\^\*(CK \*(OK \*(OK \f3-t \f2timeout\^\*(CK \*(OK \f3-u \f2unit\^\*(CK \*(OK \f2vname\f3?\f2prompt\^\f1 \*(CK \*(OK \f2vname\^ .\|.\|. \*(CK The shell input mechanism. One line is read and is broken up into fields using the characters in IFS as separators. The escape character, \e , is used to remove any special meaning for the next character and for line continuation. The -d option causes the read to continue to the first character of delim\^ rather than new-line. The -n option causes at most n\^ bytes to read rather a full line but will return when reading from a slow device as soon as any characters have been read. The -N option causes exactly n\^ to be read unless an end-of-file has been encountered or the read times out because of the -t option. In raw mode, -r, the \e character is not treated specially. The first field is assigned to the first vname , the second field to the second vname , etc., with leftover fields assigned to the last vname . When vname has the binary attribute and -n or -N is specified, the bytes that are read are stored directly into the variable. If the -v is specified, then the value of the first vname\^ will be used as a default value when reading from a terminal device. The -A option causes the variable vname\^ to be unset and each field that is read to be stored in successive elements of the indexed array vname. The -C option causes the variable vname\^ to be read as a compound variable. Blanks will be ignored when finding the beginning open parenthesis. The -p option causes the input line to be taken from the input pipe of a process spawned by the shell using \(bv& . If the -s option is present, the input will be saved as a command in the history file. The option -u can be used to specify a one digit file descriptor unit unit\^ to read from. The file descriptor can be opened with the exec\^ special built-in command. The default value of unit n\^ is 0. The option -t is used to specify a timeout in seconds when reading from a terminal or pipe. If vname\^ is omitted, then REPLY is used as the default vname . An end-of-file with the -p option causes cleanup for this process so that another can be spawned. If the first argument contains a ? , the remainder of this word is used as a prompt\^ on standard error when the shell is interactive. The exit status is 0 unless an end-of-file is encountered or read has timed out.

\(dg\(dg \f3readonly \*(OK \f3-p \*(CK \*(OK \f2vname\*(OK\f3=\f2value\^\*(CK \*(CK .\|.\|. If vname\^ is not given, the names and values of each variable with the readonly attribute is printed with the values quoted in a manner that allows them to be re-inputted. The -p option causes the word readonly to be inserted before each one. Otherwise, the given vname s are marked readonly and these names cannot be changed by subsequent assignment. When defining a type, if the value of a readonly sub-variable is not defined the value is required when creating each instance.

\(dg \f3return \*(OK \f2n\^ \*(CK Causes a shell function or \f3\|. script to return to the invoking script with the exit status specified by n . The value will be the least significant 8 bits of the specified status. If n\^ is omitted, then the return status is that of the last command executed. If return is invoked while not in a function or a \f3\|. script, then it behaves the same as exit .

\(dg \f3set \*(OK \f3\(+-BCGabefhkmnoprstuvx \*(CK \*(OK \f3\(+-o \*(OK \f2option\^ \*(CK \*(CK .\|.\|. \*(OK \f3\(+-A \f2vname\^ \*(CK \*(OK \f2arg\^ .\|.\|. \*(CK The options for this command have meaning as follows:

\(dg \f3shift \*(OK \f2n\^ \*(CK

The positional parameters from \f3$\f2n\f3+1 .\|.\|. are renamed $1 .\|.\|.\^ , default n\^ is 1. The parameter n\^ can be any arithmetic expression that evaluates to a non-negative number less than or equal to $# .

\f3sleep \f2seconds\^ Suspends execution for the number of decimal seconds or fractions of a second given by seconds .

\(dg \f3trap \*(OK \f3-p \*(CK \*(OK \f2action\^ \*(CK \*(OK \f2sig\^ \*(CK .\|.\|. The -p option causes the trap action associated with each trap as specified by the arguments to be printed with appropriate quoting. Otherwise, action\^ will be processed as if it were an argument to eval when the shell receives signal(s) sig . Each sig\^ can be given as a number or as the name of the signal. Trap commands are executed in order of signal number. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective. If action\^ is omitted and the first sig\^ is a number, or if action\^ is - , then the trap(s) for each sig\^ are reset to their original values. If action\^ is the null string then this signal is ignored by the shell and by the commands it invokes. If sig\^ is ERR then action\^ will be executed whenever a command has a non-zero exit status. If sig\^ is DEBUG then action\^ will be executed before each command. The variable .sh.command will contain the contents of the current command line when action\^ is running. If the exit status of the trap is 2 the command will not be executed. If the exit status of the trap is 255 and inside a function or a dot script, the function or dot script will return. If sig\^ is 0 or EXIT and the trap statement is executed inside the body of a function defined with the function name\^ syntax, then the command action\^ is executed after the function completes. If sig\^ is 0 or EXIT for a trap set outside any function then the command action\^ is executed on exit from the shell. If sig\^ is KEYBD , then action\^ will be executed whenever a key is read while in emacs , gmacs , or vi\^ mode. The trap command with no arguments prints a list of commands associated with each signal number.

An exit or return without an argument in a trap action will preserve the exit status of the command that invoked the trap.

\f3true Does nothing, and exits 0. Used with while for infinite loops.

\f3true Does nothing, and exits 0. Used with while for infinite loops.

\(dg\(dg \f3typeset \*(OK \f3\(+-ACHSflbnprtux\^ \*(CK \*(OK \f3\(+-EFLRXZi\*(OK\f2n\^\*(CK \*(CK \*(OK \f3-T \f2tname=(\f2assign_list) \*(CK \*(OK \f3-h \f2str \*(CK \*(OK \f3-a \*(OK\f2type\*(CK \*(CK \*(OK \f2vname\^\*(OK\f3=\f2value\^ \*(CK \^ \*(CK .\|.\|. Sets attributes and values for shell variables and functions. When invoked inside a function defined with the function name\^ syntax, a new instance of the variable vname\^ is created, and the variable's value and type are restored when the function completes. The following list of attributes may be specified:

\f3ulimit \*(OK \f3-HSacdfmnpstv \*(CK \*(OK \f2limit\^ \*(CK Set or display a resource limit. The available resource limits are listed below. Many systems do not support one or more of these limits. The limit for a specified resource is set when limit\^ is specified. The value of limit\^ can be a number in the unit specified below with each resource, or the value unlimited . The -H and -S options specify whether the hard limit or the soft limit for the given resource is set. A hard limit cannot be increased once it is set. A soft limit can be increased up to the value of the hard limit. If neither the H nor S option is specified, the limit applies to both. The current resource limit is printed when limit\^ is omitted. In this case, the soft limit is printed unless H is specified. When more than one resource is specified, then the limit name and unit is printed before the value.

\f3umask \*(OK \f3-S \*(CK \*(OK \f2mask\^ \*(CK The user file-creation mask is set to mask\^ (see umask (2)). mask can either be an octal number or a symbolic value as described in chmod (1). If a symbolic value is given, the new umask value is the complement of the result of applying mask\^ to the complement of the previous umask value. If mask\^ is omitted, the current value of the mask is printed. The -S option causes the mode to be printed as a symbolic value. Otherwise, the mask is printed in octal.

\(dg \f3unalias \*(OK \f3-a \*(CK \f2name\^ .\|.\|. The aliases given by the list of name s are removed from the alias list. The -a option causes all the aliases to be unset.

\(dg\f3unset \*(OK \f3-fnv \*(CK \f2vname\^ .\|.\|. The variables given by the list of vname s are unassigned, i.e., except for sub-variables within a type, their values and attributes are erased. For sub-variables of a type, the values are reset to the default value from the type definition. Readonly variables cannot be unset. If the -f option is set, then the names refer to function\^ names. If the -v option is set, then the names refer to variable\^ names. The -f option overrides -v . If -n is set and name\^ is a name reference, then name\^ will be unset rather than the variable that it references. The default is equivalent to -v . Unsetting LINENO , MAILCHECK , OPTARG , OPTIND , RANDOM , SECONDS , TMOUT , and _ removes their special meaning even if they are subsequently assigned to.

\f3wait \*(OK \f2job\^ .\|.\|. \*(CK Wait for the specified job and report its termination status. If job\^ is not given, then all currently active child processes are waited for. The exit status from this command is that of the last process waited for if job\^ is specified; otherwise it is zero. See Jobs for a description of the format of job .

\f3whence \*(OK \f3-afpv \*(CK \f2name\^ .\|.\|. For each name , indicate how it would be interpreted if used as a command name. The -v option produces a more verbose report. The -f option skips the search for functions. The -p option does a path search for name\^ even if name is an alias, a function, or a reserved word. The -p option turns off the -v option. The -a option is similar to the -v option but causes all interpretations of the given name to be reported.

0

8 -D Do not execute the script, but output the set of double quoted strings preceded by a $ . These strings are needed for localization of the script to different locales.

8 -E Reads the file named by the ENV variable or by \s-1$HOME\s+1/\f3.kshrc if not defined after the profiles.

10 -c If the -c option is present, then commands are read from the first arg . Any remaining arguments become positional parameters starting at 0 .

-s If the -s option is present or if no arguments remain, then commands are read from the standard input. Shell output, except for the output of the Special Commands\^ listed above, is written to file descriptor 2.

-i If the -i option is present or if the shell input and output are attached to a terminal (as told by tcgetattr (2)), then this shell is interactive . In this case \s-1TERM\s+1 is ignored (so that \f3kill 0 does not kill an interactive shell) and \s-1INTR\s+1 is caught and ignored (so that wait is interruptible). In all cases, \s-1QUIT\s+1 is ignored by the shell.

-r If the -r option is present, the shell is a restricted shell.

-D A list of all double quoted strings that are preceded by a $ will be printed on standard output and the shell will exit. This set of strings will be subject to language translation when the locale is not C or POSIX. No commands will be executed.

-P If -P or -o profile is present, the shell is a profile shell (see pfexec (1)).

-R " filename\^" The -R filename\^ option is used to generate a cross reference database that can be used by a separate utility to find definitions and references for variables and commands.

The remaining options and arguments are described under the set command above. An optional - as the first argument is ignored. Rsh\} Rksh\} Rksh93\} is used to set up login names and execution environments whose capabilities are more controlled than those of the standard shell. The actions of are identical to those of except that the following are disallowed:

The restrictions above are enforced after \f3.profile and the ENV files are interpreted.

When a command to be executed is found to be a shell procedure, invokes sh\^\} invokes ksh\^\} invokes ksh93\^\} to execute it. Thus, it is possible to provide to the end-user shell procedures that have access to the full power of the standard shell, while imposing a limited menu of commands; this scheme assumes that the end-user does not have write and execute permissions in the same directory.

The net effect of these rules is that the writer of the .profile has complete control over user actions, by performing guaranteed setup actions and leaving the user in an appropriate directory (probably not\^ the login directory).

The system administrator often sets up a directory of commands (e.g., /usr/rbin ) that can be safely invoked by

/etc/profile The system wide initialization file, executed for login shells.

/etc/ksh.kshrc The system wide startup file, executed for interactive shells. \}

\s-1$HOME\s+1/\f3.profile The personal initialization file, executed for login shells after /etc/profile.

\s-1$HOME\s+1/\f3..kshrc Default personal initialization file, executed for interactive shells when ENV is not set.

/etc/suid_profile Alternative initialization file, executed when instead of personal initialization file when the real and effective user or group id do not match.

/dev/null NULL device

Morris I. Bolsky and David G. Korn, "The New KornShell Command and Programming Language" , Prentice Hall, 1995.

"POSIX - Part 2: Shell and Utilities," IEEE Std 1003.2-1992, ISO/IEC 9945-2, IEEE, 1993.

If a command is executed, and then a command with the same name is installed in a directory in the search path before the directory where the original command was found, the shell will continue to exec\^ the original command. Use the -t option of the alias\^ command to correct this situation.

Some very old shell scripts contain a ^ as a synonym for the pipe character \(bv .

Using the hist\^ built-in command within a compound command will cause the whole command to disappear from the history file.

The built-in command \f3\|. \f2file\^ reads the whole file before any commands are executed. Therefore, alias and unalias commands in the file will not apply to any commands defined in the file.

Traps are not processed while a job is waiting for a foreground process. Thus, a trap on CHLD won't be executed until the foreground job terminates.

It is a good idea to leave a space after the comma operator in arithmetic expressions to prevent the comma from being interpreted as the decimal point character in certain locales.