1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Kenneth Almquist. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 36.\" $FreeBSD$ 37.\" 38.Dd May 5, 1995 39.Dt SH 1 40.Os 41.Sh NAME 42.Nm sh 43.Nd command interpreter (shell) 44.Sh SYNOPSIS 45.Nm 46.Op Fl /+abCEefIimnPpsTuVvx 47.Op Fl /+o Ar longname 48.Op Fl c Ar string 49.Op Ar arg ... 50.Sh DESCRIPTION 51The 52.Nm 53utility is the standard command interpreter for the system. 54The current version of 55.Nm 56is in the process of being changed to 57conform with the 58.St -p1003.2 59specification for the shell. This version has many features which make 60it appear 61similar in some respects to the Korn shell, but it is not a Korn 62shell clone like 63.Xr pdksh 1 . 64Only features 65designated by POSIX, plus a few Berkeley extensions, are being 66incorporated into this shell. 67This man page is not intended to be a tutorial nor a complete 68specification of the shell. 69.Ss Overview 70The shell is a command that reads lines from 71either a file or the terminal, interprets them, and 72generally executes other commands. 73It is the program that is started when a user logs into the system, 74although a user can select a different shell with the 75.Xr chsh 1 76command. 77The shell 78implements a language that has flow control constructs, 79a macro facility that provides a variety of features in 80addition to data storage, along with built-in history and line 81editing capabilities. It incorporates many features to 82aid interactive use and has the advantage that the interpretative 83language is common to both interactive and non-interactive 84use (shell scripts). That is, commands can be typed directly 85to the running shell or can be put into a file, 86which can be executed directly by the shell. 87.Ss Invocation 88.\" 89.\" XXX This next sentence is incredibly confusing. 90.\" 91If no arguments are present and if the standard input of the shell 92is connected to a terminal 93(or if the 94.Fl i 95option is set), 96the shell is considered an interactive shell. An interactive shell 97generally prompts before each command and handles programming 98and command errors differently (as described below). 99When first starting, the shell inspects argument 0, and 100if it begins with a dash 101.Pq Li - , 102the shell is also considered a login shell. 103This is normally done automatically by the system 104when the user first logs in. A login shell first reads commands 105from the files 106.Pa /etc/profile 107and then 108.Pa .profile 109if they exist. If the environment variable 110.Ev ENV 111is set on entry to a shell, or is set in the 112.Pa .profile 113of a login shell, the shell then reads commands from the file named in 114.Ev ENV . 115Therefore, a user should place commands that are to be executed only 116at login time in the 117.Pa .profile 118file, and commands that are executed for every shell inside the 119.Ev ENV 120file. 121The user can set the 122.Ev ENV 123variable to some file by placing the following line in the file 124.Pa .profile 125in the home directory, 126substituting for 127.Pa .shinit 128the filename desired: 129.Pp 130.Dl ENV=$HOME/.shinit; export ENV 131.Pp 132The first non-option argument specified on the command line 133will be treated as the 134name of a file from which to read commands (a shell script), and 135the remaining arguments are set as the positional parameters 136of the shell ($1, $2, etc). Otherwise, the shell reads commands 137from its standard input. 138.Pp 139Unlike older versions of 140.Nm 141the 142.Ev ENV 143script is only sourced on invocation of interactive shells. This 144closes a well-known, and sometimes easily exploitable security 145hole related to poorly thought out 146.Ev ENV 147scripts. 148.Ss Argument List Processing 149All of the single letter options to 150.Nm 151have a corresponding long name, 152with the exception of 153.Fl c 154and 155.Fl /+o . 156These long names are provided next to the single letter options 157in the descriptions below. 158The long name for an option may be specified as an argument to the 159.Fl /+o 160option of 161.Xr sh 1 . 162Once the shell is running, 163the long name for an option may be specified as an argument to the 164.Fl /+o 165option of the 166.Ic set 167built-in command 168(described later in the section called 169.Sx Built-in Commands ) . 170Introducing an option with a dash 171.Pq Li - 172enables the option, 173while using a plus 174.Pq Li + 175disables the option. 176A 177.Dq Li -- 178or plain 179.Dq Li - 180will stop option processing and will force the remaining 181words on the command line to be treated as arguments. 182The 183.Fl /+o 184and 185.Fl c 186options do not have long names. 187They take arguments and are described after the single letter options. 188.Bl -tag -width indent 189.It Fl a Li allexport 190Flag variables for export when assignments are made to them. 191.It Fl b Li notify 192Enable asynchronous notification of background job 193completion. 194(UNIMPLEMENTED) 195.It Fl C Li noclobber 196Do not overwrite existing files with 197.Dq Li > . 198.It Fl E Li emacs 199Enable the built-in 200.Xr emacs 1 201command line editor (disables the 202.Fl V 203option if it has been set). 204.It Fl e Li errexit 205Exit immediately if any untested command fails in non-interactive mode. 206The exit status of a command is considered to be 207explicitly tested if the command is used to control 208an if, elif, while, or until; or if the command is the left 209hand operand of an 210.Dq Li && 211or 212.Dq Li || 213operator. 214.It Fl f Li noglob 215Disable pathname expansion. 216.It Fl I Li ignoreeof 217Ignore 218.Dv EOF Ns ' Ns s 219from input when in interactive mode. 220.It Fl i Li interactive 221Force the shell to behave interactively. 222.It Fl m Li monitor 223Turn on job control (set automatically when interactive). 224.It Fl n Li noexec 225If not interactive, read commands but do not 226execute them. This is useful for checking the 227syntax of shell scripts. 228.It Fl P Li physical 229Change the default for the 230.Ic cd 231and 232.Ic pwd 233commands from 234.Fl L 235(logical directory layout) 236to 237.Fl P 238(physical directory layout). 239.It Fl p Li privileged 240Turn on privileged mode. This mode is enabled on startup 241if either the effective user or group id is not equal to the 242real user or group id. Turning this mode off sets the 243effective user and group ids to the real user and group ids. 244When this mode is enabled for interactive shells, the file 245.Pa /etc/suid_profile 246is sourced instead of 247.Pa ~/.profile 248after 249.Pa /etc/profile 250is sourced, and the contents of the 251.Ev ENV 252variable are ignored. 253.It Fl s Li stdin 254Read commands from standard input (set automatically 255if no file arguments are present). This option has 256no effect when set after the shell has already started 257running (i.e. when set with the 258.Ic set 259command). 260.It Fl T Li asynctraps 261When waiting for a child, execute traps immediately. 262If this option is not set, 263traps are executed after the child exits, 264as specified in 265.St -p1003.2 266This nonstandard option is useful for putting guarding shells around 267children that block signals. The surrounding shell may kill the child 268or it may just return control to the tty and leave the child alone, 269like this: 270.Bd -literal -offset indent 271sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 272.Ed 273.Pp 274.It Fl u Li nounset 275Write a message to standard error when attempting 276to expand a variable that is not set, and if the 277shell is not interactive, exit immediately. 278.It Fl V Li vi 279Enable the built-in 280.Xr vi 1 281command line editor (disables 282.Fl E 283if it has been set). 284.It Fl v Li verbose 285The shell writes its input to standard error 286as it is read. Useful for debugging. 287.It Fl x Li xtrace 288Write each command 289(preceded by 290.Dq Li +\ ) 291to standard error before it is executed. 292Useful for debugging. 293.El 294.Pp 295The 296.Fl c 297option may be used to pass its string argument to the shell 298to be interpreted as input. 299Keep in mind that this option only accepts a single string as its 300argument, hence multi-word strings must be quoted. 301.Pp 302The 303.Fl /+o 304option takes as its only argument the long name of an option 305to be enabled or disabled. 306For example, the following two invocations of 307.Nm 308both enable the built-in 309.Xr emacs 1 310command line editor: 311.Bd -literal -offset indent 312set -E 313set -o emacs 314.Ed 315.Pp 316If used without an argument, the 317.Fl o 318option displays the current option settings in a human-readable format. 319If 320.Cm +o 321is used without an argument, the current option settings are output 322in a format suitable for re-input into the shell. 323.Ss Lexical Structure 324The shell reads input in terms of lines from a file and breaks 325it up into words at whitespace (blanks and tabs), and at 326certain sequences of 327characters called 328.Dq operators , 329which are special to the shell. 330There are two types of operators: control operators and 331redirection operators (their meaning is discussed later). 332The following is a list of valid operators: 333.Bl -tag -width indent 334.It Control operators: 335.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 336.It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en 337.It Li ;; Ta Li ; Ta Li | Ta Li || 338.El 339.It Redirection operators: 340.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 341.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 342.It Li <& Ta Li >& Ta Li <<- Ta Li >| 343.El 344.El 345.Ss Quoting 346Quoting is used to remove the special meaning of certain characters 347or words to the shell, such as operators, whitespace, or 348keywords. There are three types of quoting: matched single quotes, 349matched double quotes, and backslash. 350.Bl -tag -width indent 351.It Single Quotes 352Enclosing characters in single quotes preserves the literal 353meaning of all the characters (except single quotes, making 354it impossible to put single-quotes in a single-quoted string). 355.It Double Quotes 356Enclosing characters within double quotes preserves the literal 357meaning of all characters except dollarsign 358.Pq Li $ , 359backquote 360.Pq Li ` , 361and backslash 362.Pq Li \e . 363The backslash inside double quotes is historically weird. 364It remains literal unless it precedes the following characters, 365which it serves to quote: 366.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 367.It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en 368.El 369.It Backslash 370A backslash preserves the literal meaning of the following 371character, with the exception of the newline character 372.Pq Li \en . 373A backslash preceding a newline is treated as a line continuation. 374.El 375.Ss Reserved Words 376Reserved words are words that have special meaning to the 377shell and are recognized at the beginning of a line and 378after a control operator. The following are reserved words: 379.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 380.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 381.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 382.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 383.El 384.Ss Aliases 385An alias is a name and corresponding value set using the 386.Ic alias 387built-in command. Whenever a reserved word may occur (see above), 388and after checking for reserved words, the shell 389checks the word to see if it matches an alias. 390If it does, it replaces it in the input stream with its value. 391For example, if there is an alias called 392.Dq Li lf 393with the value 394.Dq Li ls -F , 395then the input 396.Bd -literal -offset indent 397lf foobar 398.Ed 399.Pp 400would become 401.Bd -literal -offset indent 402ls -F foobar 403.Ed 404.Pp 405Aliases provide a convenient way for naive users to 406create shorthands for commands without having to learn how 407to create functions with arguments. They can also be 408used to create lexically obscure code. This use is discouraged. 409.Ss Commands 410The shell interprets the words it reads according to a 411language, the specification of which is outside the scope 412of this man page (refer to the BNF in the 413.St -p1003.2 414document). Essentially though, a line is read and if 415the first word of the line (or after a control operator) 416is not a reserved word, then the shell has recognized a 417simple command. Otherwise, a complex command or some 418other special construct may have been recognized. 419.Ss Simple Commands 420If a simple command has been recognized, the shell performs 421the following actions: 422.Bl -enum 423.It 424Leading words of the form 425.Dq Li name=value 426are stripped off and assigned to the environment of 427the simple command. Redirection operators and 428their arguments (as described below) are stripped 429off and saved for processing. 430.It 431The remaining words are expanded as described in 432the section called 433.Sx Word Expansions , 434and the first remaining word is considered the command 435name and the command is located. The remaining 436words are considered the arguments of the command. 437If no command name resulted, then the 438.Dq Li name=value 439variable assignments recognized in 1) affect the 440current shell. 441.It 442Redirections are performed as described in 443the next section. 444.El 445.Ss Redirections 446Redirections are used to change where a command reads its input 447or sends its output. In general, redirections open, close, or 448duplicate an existing reference to a file. The overall format 449used for redirection is: 450.Pp 451.Dl [n] redir-op file 452.Pp 453The 454.Ql redir-op 455is one of the redirection operators mentioned 456previously. The following gives some examples of how these 457operators can be used. 458Note that stdin and stdout are commonly used abbreviations 459for standard input and standard output respectively. 460.Bl -tag -width "1234567890XX" -offset indent 461.It Li [n]> file 462redirect stdout (or file descriptor n) to file 463.It Li [n]>| file 464same as above, but override the 465.Fl C 466option 467.It Li [n]>> file 468append stdout (or file descriptor n) to file 469.It Li [n]< file 470redirect stdin (or file descriptor n) from file 471.It Li [n]<> file 472redirect stdin (or file descriptor n) to and from file 473.It Li [n1]<&n2 474duplicate stdin (or file descriptor n1) from file descriptor n2 475.It Li [n]<&- 476close stdin (or file descriptor n) 477.It Li [n1]>&n2 478duplicate stdout (or file descriptor n1) to file descriptor n2 479.It Li [n]>&- 480close stdout (or file descriptor n) 481.El 482.Pp 483The following redirection is often called a 484.Dq here-document . 485.Bd -literal -offset indent 486[n]<< delimiter 487 here-doc-text 488 ... 489delimiter 490.Ed 491.Pp 492All the text on successive lines up to the delimiter is 493saved away and made available to the command on standard 494input, or file descriptor n if it is specified. If the delimiter 495as specified on the initial line is quoted, then the here-doc-text 496is treated literally, otherwise the text is subjected to 497parameter expansion, command substitution, and arithmetic 498expansion (as described in the section on 499.Sx Word Expansions ) . 500If the operator is 501.Dq Li <<- 502instead of 503.Dq Li << , 504then leading tabs 505in the here-doc-text are stripped. 506.Ss Search and Execution 507There are three types of commands: shell functions, 508built-in commands, and normal programs. 509The command is searched for (by name) in that order. 510The three types of commands are all executed in a different way. 511.Pp 512When a shell function is executed, all of the shell positional 513parameters (except $0, which remains unchanged) are 514set to the arguments of the shell function. 515The variables which are explicitly placed in the environment of 516the command (by placing assignments to them before the 517function name) are made local to the function and are set 518to the values given. 519Then the command given in the function definition is executed. 520The positional parameters are restored to their original values 521when the command completes. 522This all occurs within the current shell. 523.Pp 524Shell built-in commands are executed internally to the shell, without 525spawning a new process. 526.Pp 527Otherwise, if the command name does not match a function 528or built-in command, the command is searched for as a normal 529program in the file system (as described in the next section). 530When a normal program is executed, the shell runs the program, 531passing the arguments and the environment to the program. 532If the program is not a normal executable file 533(i.e. if it does not begin with the 534.Qq magic number 535whose 536.Tn ASCII 537representation is 538.Qq #! , 539resulting in an 540.Er ENOEXEC 541return value from 542.Xr execve 2 ) 543the shell will interpret the program in a subshell. 544The child shell will reinitialize itself in this case, 545so that the effect will be 546as if a new shell had been invoked to handle the ad-hoc shell script, 547except that the location of hashed commands located in 548the parent shell will be remembered by the child. 549.Pp 550Note that previous versions of this document 551and the source code itself misleadingly and sporadically 552refer to a shell script without a magic number 553as a 554.Qq shell procedure . 555.Ss Path Search 556When locating a command, the shell first looks to see if 557it has a shell function by that name. Then it looks for a 558built-in command by that name. If a built-in command is not found, 559one of two things happen: 560.Bl -enum 561.It 562Command names containing a slash are simply executed without 563performing any searches. 564.It 565The shell searches each entry in 566.Ev PATH 567in turn for the command. The value of the 568.Ev PATH 569variable should be a series of 570entries separated by colons. Each entry consists of a 571directory name. 572The current directory 573may be indicated implicitly by an empty directory name, 574or explicitly by a single period. 575.El 576.Ss Command Exit Status 577Each command has an exit status that can influence the behavior 578of other shell commands. The paradigm is that a command exits 579with zero for normal or success, and non-zero for failure, 580error, or a false indication. The man page for each command 581should indicate the various exit codes and what they mean. 582Additionally, the built-in commands return exit codes, as does 583an executed shell function. 584.Pp 585If a command is terminated by a signal, its exit status is 128 plus 586the signal number. Signal numbers are defined in the header file 587.Aq Pa sys/signal.h . 588.Ss Complex Commands 589Complex commands are combinations of simple commands 590with control operators or reserved words, together creating a larger complex 591command. More generally, a command is one of the following: 592.Bl -item -offset indent 593.It 594simple command 595.It 596pipeline 597.It 598list or compound-list 599.It 600compound command 601.It 602function definition 603.El 604.Pp 605Unless otherwise stated, the exit status of a command is 606that of the last simple command executed by the command. 607.Ss Pipelines 608A pipeline is a sequence of one or more commands separated 609by the control operator |. The standard output of all but 610the last command is connected to the standard input 611of the next command. The standard output of the last 612command is inherited from the shell, as usual. 613.Pp 614The format for a pipeline is: 615.Pp 616.Dl [!] command1 [ | command2 ...] 617.Pp 618The standard output of command1 is connected to the standard 619input of command2. The standard input, standard output, or 620both of a command is considered to be assigned by the 621pipeline before any redirection specified by redirection 622operators that are part of the command. 623.Pp 624If the pipeline is not in the background (discussed later), 625the shell waits for all commands to complete. 626.Pp 627If the reserved word ! does not precede the pipeline, the 628exit status is the exit status of the last command specified 629in the pipeline. Otherwise, the exit status is the logical 630NOT of the exit status of the last command. That is, if 631the last command returns zero, the exit status is 1; if 632the last command returns greater than zero, the exit status 633is zero. 634.Pp 635Because pipeline assignment of standard input or standard 636output or both takes place before redirection, it can be 637modified by redirection. For example: 638.Pp 639.Dl $ command1 2>&1 | command2 640.Pp 641sends both the standard output and standard error of 642.Ql command1 643to the standard input of 644.Ql command2 . 645.Pp 646A 647.Dq Li \&; 648or newline terminator causes the preceding 649AND-OR-list 650(described below in the section called 651.Sx Short-Circuit List Operators ) 652to be executed sequentially; 653an 654.Dq Li & 655causes asynchronous execution of the preceding AND-OR-list. 656.Pp 657Note that unlike some other shells, 658.Nm 659executes each process in the pipeline as a child of the 660.Nm 661process. 662Shell built-in commands are the exception to this rule. 663They are executed in the current shell, although they do not affect its 664environment when used in pipelines. 665.Ss Background Commands (&) 666If a command is terminated by the control operator ampersand 667.Pq Li & , 668the shell executes the command asynchronously; 669the shell does not wait for the command to finish 670before executing the next command. 671.Pp 672The format for running a command in background is: 673.Bd -literal -offset indent 674command1 & [command2 & ...] 675.Ed 676.Pp 677If the shell is not interactive, the standard input of an 678asynchronous command is set to /dev/null. 679.Ss Lists (Generally Speaking) 680A list is a sequence of zero or more commands separated by 681newlines, semicolons, or ampersands, 682and optionally terminated by one of these three characters. 683The commands in a 684list are executed in the order they are written. 685If command is followed by an ampersand, the shell starts the 686command and immediately proceeds onto the next command; 687otherwise it waits for the command to terminate before 688proceeding to the next one. 689.Ss Short-Circuit List Operators 690.Dq Li && 691and 692.Dq Li || 693are AND-OR list operators. 694.Dq Li && 695executes the first command, and then executes the second command 696if the exit status of the first command is zero. 697.Dq Li || 698is similar, but executes the second command if the exit 699status of the first command is nonzero. 700.Dq Li && 701and 702.Dq Li || 703both have the same priority. 704.Ss Flow-Control Constructs (if, while, for, case) 705The syntax of the 706.Ic if 707command is: 708.\" 709.\" XXX Use .Dl to work around broken handling of .Ic inside .Bd and .Ed . 710.\" 711.Dl Ic if Ar list 712.Dl Ic then Ar list 713.Dl [ Ic elif Ar list 714.Dl Ic then Ar list ] ... 715.Dl [ Ic else Ar list ] 716.Dl Ic fi 717.Pp 718The syntax of the 719.Ic while 720command is: 721.Dl Ic while Ar list 722.Dl Ic do Ar list 723.Dl Ic done 724.Pp 725The two lists are executed repeatedly while the exit status of the 726first list is zero. 727The 728.Ic until 729command is similar, but has the word 730.Ic until 731in place of 732.Ic while , 733which causes it to 734repeat until the exit status of the first list is zero. 735.Pp 736The syntax of the 737.Ic for 738command is: 739.Dl Ic for Ar variable Ic in Ar word ... 740.Dl Ic do Ar list 741.Dl Ic done 742.Pp 743The words are expanded, and then the list is executed 744repeatedly with the variable set to each word in turn. 745The 746.Ic do 747and 748.Ic done 749commands may be replaced with 750.Dq Li { 751and 752.Dq Li } . 753.Pp 754The syntax of the 755.Ic break 756and 757.Ic continue 758commands is: 759.Dl Ic break Op Ar num 760.Dl Ic continue Op Ar num 761.Pp 762The 763.Ic break 764command terminates the 765.Ar num 766innermost 767.Ic for 768or 769.Ic while 770loops. 771The 772.Ic continue 773command continues with the next iteration of the innermost loop. 774These are implemented as built-in commands. 775.Pp 776The syntax of the 777.Ic case 778command is 779.Dl Ic case Ar word Ic in 780.Dl pattern) list ;; 781.Dl ... 782.Dl Ic esac 783.Pp 784The pattern can actually be one or more patterns 785(see 786.Sx Shell Patterns 787described later), 788separated by 789.Dq Li \&| 790characters. 791.Ss Grouping Commands Together 792Commands may be grouped by writing either 793.Bd -literal -offset indent 794(list) 795.Ed 796.Pp 797or 798.Bd -literal -offset indent 799{ list; } 800.Ed 801.Pp 802The first form executes the commands in a subshell. 803Note that built-in commands thus executed do not affect the current shell. 804The second form does not fork another shell, 805so it is slightly more efficient. 806Grouping commands together this way allows the user to 807redirect their output as though they were one program: 808.Bd -literal -offset indent 809{ echo -n "hello"; echo " world"; } > greeting 810.Ed 811.Ss Functions 812The syntax of a function definition is 813.Bd -literal -offset indent 814name ( ) command 815.Ed 816.Pp 817A function definition is an executable statement; when 818executed it installs a function named name and returns an 819exit status of zero. The command is normally a list 820enclosed between 821.Dq Li { 822and 823.Dq Li } . 824.Pp 825Variables may be declared to be local to a function by 826using the 827.Ic local 828command. 829This should appear as the first statement of a function, 830and the syntax is: 831.Bd -ragged -offset indent 832.Ic local 833.Op Ar variable ... 834.Op Ar - 835.Ed 836.Pp 837The 838.Ic local 839command is implemented as a built-in command. 840.Pp 841When a variable is made local, it inherits the initial 842value and exported and readonly flags from the variable 843with the same name in the surrounding scope, if there is 844one. Otherwise, the variable is initially unset. The shell 845uses dynamic scoping, so that if the variable 846.Em x 847is made local to function 848.Em f , 849which then calls function 850.Em g , 851references to the variable 852.Em x 853made inside 854.Em g 855will refer to the variable 856.Em x 857declared inside 858.Em f , 859not to the global variable named 860.Em x . 861.Pp 862The only special parameter than can be made local is 863.Dq Li - . 864Making 865.Dq Li - 866local causes any shell options that are 867changed via the set command inside the function to be 868restored to their original values when the function 869returns. 870.Pp 871The syntax of the 872.Ic return 873command is 874.Bd -ragged -offset indent 875.Ic return 876.Op Ar exitstatus 877.Ed 878.Pp 879It terminates the currently executing function. 880The 881.Ic return 882command is implemented as a built-in command. 883.Ss Variables and Parameters 884The shell maintains a set of parameters. A parameter 885denoted by a name is called a variable. When starting up, 886the shell turns all the environment variables into shell 887variables. New variables can be set using the form 888.Bd -literal -offset indent 889name=value 890.Ed 891.Pp 892Variables set by the user must have a name consisting solely 893of alphabetics, numerics, and underscores. 894The first letter of a variable name must not be numeric. 895A parameter can also be denoted by a number 896or a special character as explained below. 897.Ss Positional Parameters 898A positional parameter is a parameter denoted by a number greater than zero. 899The shell sets these initially to the values of its command line 900arguments that follow the name of the shell script. The 901.Ic set 902built-in command can also be used to set or reset them. 903.Ss Special Parameters 904A special parameter is a parameter denoted by one of the following 905special characters. The value of the parameter is listed 906next to its character. 907.Bl -hang 908.It Li * 909Expands to the positional parameters, starting from one. When 910the expansion occurs within a double-quoted string 911it expands to a single field with the value of each parameter 912separated by the first character of the 913.Ev IFS 914variable, 915or by a 916.Aq space 917if 918.Ev IFS 919is unset. 920.It Li @ 921Expands to the positional parameters, starting from one. When 922the expansion occurs within double-quotes, each positional 923parameter expands as a separate argument. 924If there are no positional parameters, the 925expansion of 926.Li @ 927generates zero arguments, even when 928.Li @ 929is double-quoted. What this basically means, for example, is 930if $1 is 931.Dq abc 932and $2 is 933.Dq def ghi , 934then 935.Qq Li $@ 936expands to 937the two arguments: 938.Bd -literal -offset indent 939"abc" "def ghi" 940.Ed 941.It Li # 942Expands to the number of positional parameters. 943.It Li \&? 944Expands to the exit status of the most recent pipeline. 945.It Li - 946(hyphen) Expands to the current option flags (the single-letter 947option names concatenated into a string) as specified on 948invocation, by the set built-in command, or implicitly 949by the shell. 950.It Li $ 951Expands to the process ID of the invoked shell. A subshell 952retains the same value of $ as its parent. 953.It Li \&! 954Expands to the process ID of the most recent background 955command executed from the current shell. For a 956pipeline, the process ID is that of the last command in the 957pipeline. 958.It Li 0 959(zero) Expands to the name of the shell or shell script. 960.El 961.Ss Word Expansions 962This clause describes the various expansions that are 963performed on words. Not all expansions are performed on 964every word, as explained later. 965.Pp 966Tilde expansions, parameter expansions, command substitutions, 967arithmetic expansions, and quote removals that occur within 968a single word expand to a single field. It is only field 969splitting or pathname expansion that can create multiple 970fields from a single word. 971The single exception to this rule is 972the expansion of the special parameter 973.Li @ 974within double-quotes, 975as was described above. 976.Pp 977The order of word expansion is: 978.Bl -enum 979.It 980Tilde Expansion, Parameter Expansion, Command Substitution, 981Arithmetic Expansion (these all occur at the same time). 982.It 983Field Splitting is performed on fields generated by step (1) 984unless the 985.Ev IFS 986variable is null. 987.It 988Pathname Expansion (unless the 989.Fl f 990option is in effect). 991.It 992Quote Removal. 993.El 994.Pp 995The 996.Dq Li $ 997character is used to introduce parameter expansion, command 998substitution, or arithmetic evaluation. 999.Ss Tilde Expansion (substituting a user's home directory) 1000A word beginning with an unquoted tilde character 1001.Pq Li ~ 1002is 1003subjected to tilde expansion. 1004All the characters up to a slash 1005.Pq Li / 1006or the end of the word are treated as a username 1007and are replaced with the user's home directory. If the 1008username is missing (as in ~/foobar), the tilde is replaced 1009with the value of the HOME variable (the current user's 1010home directory). 1011.Ss Parameter Expansion 1012The format for parameter expansion is as follows: 1013.Bd -literal -offset indent 1014${expression} 1015.Ed 1016.Pp 1017where expression consists of all characters until the matching 1018.Dq Li } . 1019Any 1020.Dq Li } 1021escaped by a backslash or within a quoted string, and characters in 1022embedded arithmetic expansions, command substitutions, and variable 1023expansions, are not examined in determining the matching 1024.Dq Li } . 1025.Pp 1026The simplest form for parameter expansion is: 1027.Bd -literal -offset indent 1028${parameter} 1029.Ed 1030.Pp 1031The value, if any, of parameter is substituted. 1032.Pp 1033The parameter name or symbol can be enclosed in braces, which are 1034optional except for positional parameters with more than one digit or 1035when parameter is followed by a character that could be interpreted as 1036part of the name. 1037If a parameter expansion occurs inside double-quotes: 1038.Bl -enum 1039.It 1040Pathname expansion is not performed on the results of the 1041expansion. 1042.It 1043Field splitting is not performed on the results of the 1044expansion, with the exception of the special parameter 1045.Li @ . 1046.El 1047.Pp 1048In addition, a parameter expansion can be modified by using one of the 1049following formats. 1050.Bl -tag -width indent 1051.It Li ${parameter:-word} 1052Use Default Values. If parameter is unset or 1053null, the expansion of word is 1054substituted; otherwise, the value of 1055parameter is substituted. 1056.It Li ${parameter:=word} 1057Assign Default Values. If parameter is unset 1058or null, the expansion of word is 1059assigned to parameter. In all cases, the 1060final value of parameter is 1061substituted. Only variables, not positional 1062parameters or special parameters, can be 1063assigned in this way. 1064.It Li ${parameter:?[word]} 1065Indicate Error if Null or Unset. If 1066parameter is unset or null, the expansion of 1067word (or a message indicating it is unset if 1068word is omitted) is written to standard 1069error and the shell exits with a nonzero 1070exit status. 1071Otherwise, the value of 1072parameter is substituted. An 1073interactive shell need not exit. 1074.It Li ${parameter:+word} 1075Use Alternate Value. If parameter is unset 1076or null, null is substituted; 1077otherwise, the expansion of word is 1078substituted. 1079.Pp 1080In the parameter expansions shown previously, use of the colon in the 1081format results in a test for a parameter that is unset or null; omission 1082of the colon results in a test for a parameter that is only unset. 1083.It Li ${#parameter} 1084String Length. The length in characters of 1085the value of parameter. 1086.El 1087.Pp 1088The following four varieties of parameter expansion provide for substring 1089processing. 1090In each case, pattern matching notation 1091(see 1092.Sx Shell Patterns ) , 1093rather than regular expression notation, 1094is used to evaluate the patterns. 1095If parameter is one of the special parameters 1096.Li * 1097or 1098.Li @ , 1099the result of the expansion is unspecified. 1100Enclosing the full parameter expansion string in double-quotes does not 1101cause the following four varieties of pattern characters to be quoted, 1102whereas quoting characters within the braces has this effect. 1103.Bl -tag -width indent 1104.It Li ${parameter%word} 1105Remove Smallest Suffix Pattern. The word 1106is expanded to produce a pattern. The 1107parameter expansion then results in 1108parameter, with the smallest portion of the 1109suffix matched by the pattern deleted. 1110.It Li ${parameter%%word} 1111Remove Largest Suffix Pattern. The word 1112is expanded to produce a pattern. The 1113parameter expansion then results in 1114parameter, with the largest portion of the 1115suffix matched by the pattern deleted. 1116.It Li ${parameter#word} 1117Remove Smallest Prefix Pattern. The word 1118is expanded to produce a pattern. The 1119parameter expansion then results in 1120parameter, with the smallest portion of the 1121prefix matched by the pattern deleted. 1122.It Li ${parameter##word} 1123Remove Largest Prefix Pattern. The word 1124is expanded to produce a pattern. The 1125parameter expansion then results in 1126parameter, with the largest portion of the 1127prefix matched by the pattern deleted. 1128.El 1129.Ss Command Substitution 1130Command substitution allows the output of a command to be substituted in 1131place of the command name itself. Command substitution occurs when 1132the command is enclosed as follows: 1133.Bd -literal -offset indent 1134$(command) 1135.Ed 1136.Pp 1137or the backquoted version: 1138.Bd -literal -offset indent 1139`command` 1140.Ed 1141.Pp 1142The shell expands the command substitution by executing command in a 1143subshell environment and replacing the command substitution 1144with the standard output of the command, 1145removing sequences of one or more newlines at the end of the substitution. 1146Embedded newlines before the end of the output are not removed; 1147however, during field splitting, they may be translated into spaces 1148depending on the value of 1149.Ev IFS 1150and the quoting that is in effect. 1151.Ss Arithmetic Expansion 1152Arithmetic expansion provides a mechanism for evaluating an arithmetic 1153expression and substituting its value. 1154The format for arithmetic expansion is as follows: 1155.Bd -literal -offset indent 1156$((expression)) 1157.Ed 1158.Pp 1159The expression is treated as if it were in double-quotes, except 1160that a double-quote inside the expression is not treated specially. The 1161shell expands all tokens in the expression for parameter expansion, 1162command substitution, and quote removal. 1163.Pp 1164Next, the shell treats this as an arithmetic expression and 1165substitutes the value of the expression. 1166.Ss White Space Splitting (Field Splitting) 1167After parameter expansion, command substitution, and 1168arithmetic expansion the shell scans the results of 1169expansions and substitutions that did not occur in double-quotes for 1170field splitting and multiple fields can result. 1171.Pp 1172The shell treats each character of the 1173.Ev IFS 1174as a delimiter and uses 1175the delimiters to split the results of parameter expansion and command 1176substitution into fields. 1177.Ss Pathname Expansion (File Name Generation) 1178Unless the 1179.Fl f 1180option is set, 1181file name generation is performed 1182after word splitting is complete. Each word is 1183viewed as a series of patterns, separated by slashes. The 1184process of expansion replaces the word with the names of 1185all existing files whose names can be formed by replacing 1186each pattern with a string that matches the specified pattern. 1187There are two restrictions on this: first, a pattern cannot match 1188a string containing a slash, and second, 1189a pattern cannot match a string starting with a period 1190unless the first character of the pattern is a period. 1191The next section describes the patterns used for both 1192Pathname Expansion and the 1193.Ic case 1194command. 1195.Ss Shell Patterns 1196A pattern consists of normal characters, which match themselves, 1197and meta-characters. 1198The meta-characters are 1199.Dq Li \&! , 1200.Dq Li * , 1201.Dq Li \&? , 1202and 1203.Dq Li [ . 1204These characters lose their special meanings if they are quoted. 1205When command or variable substitution is performed and the dollar sign 1206or back quotes are not double-quoted, the value of the 1207variable or the output of the command is scanned for these 1208characters and they are turned into meta-characters. 1209.Pp 1210An asterisk 1211.Pq Li * 1212matches any string of characters. 1213A question mark 1214.Pq Li \&? 1215matches any single character. 1216A left bracket 1217.Pq Li [ 1218introduces a character class. 1219The end of the character class is indicated by a 1220.Dq Li \&] ; 1221if the 1222.Dq Li \&] 1223is missing then the 1224.Dq Li [ 1225matches a 1226.Dq Li [ 1227rather than introducing a character class. 1228A character class matches any of the characters between the square brackets. 1229A range of characters may be specified using a minus sign. 1230The character class may be complemented by making an exclamation point 1231.Pq Li !\& 1232the first character of the character class. 1233.Pp 1234To include a 1235.Dq Li \&] 1236in a character class, make it the first character listed 1237(after the 1238.Dq Li \&! , 1239if any). 1240To include a 1241.Dq Li - , 1242make it the first or last character listed. 1243.Ss Built-in Commands 1244This section lists the commands which 1245are built-in because they need to perform some operation 1246that cannot be performed by a separate process. In addition to 1247these, a built-in version of the 1248.Xr test 1 1249command is provided for efficiency. 1250.Bl -tag -width indent 1251.It Ic \&: 1252A null command that returns a 0 (true) exit value. 1253.It Ic \&. Ar file 1254The commands in the specified file are read and executed by the shell. 1255If 1256.Ar file 1257contains any 1258.Dq / 1259characters, it is used as is. Otherwise, the shell searches the 1260.Ev PATH 1261for the file. If it is not found in the 1262.Ev PATH , 1263it is sought in the current working directory. 1264.It Ic alias Op Ar name ... 1265.It Ic alias Op Ar name Ns = Ns Ar string ... 1266If 1267.Ar name Ns = Ns Ar string 1268is specified, the shell defines the alias 1269.Ar name 1270with value 1271.Ar string . 1272If just 1273.Ar name 1274is specified, the value of the alias 1275.Ar name 1276is printed. 1277With no arguments, the 1278.Ic alias 1279built-in command prints the names and values of all defined aliases 1280(see 1281.Ic unalias ) . 1282Alias values are written with appropriate quoting so that they are 1283suitable for re-input to the shell. 1284.It Ic bg Op Ar job ... 1285Continue the specified jobs 1286(or the current job if no jobs are given) 1287in the background. 1288.It Ic builtin Ar cmd Op Ar arg ... 1289Execute the specified built-in command, 1290.Ar cmd . 1291This is useful when the user wishes to override a shell function 1292with the same name as a built-in command. 1293.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1294List or alter key bindings for the line editor. 1295This command is documented in 1296.Xr editrc 5 . 1297.It Ic cd Oo Fl LP Oc Op Ar directory 1298Switch to the specified 1299.Ar directory , 1300or to the directory specified in the 1301.Ev HOME 1302environment variable if no 1303.Ar directory 1304is specified. 1305If 1306.Ar directory 1307does not begin with 1308.Pa / , \&. , 1309or 1310.Pa .. , 1311then the directories listed in the 1312.Ev CDPATH 1313variable will be 1314searched for the specified 1315.Ar directory . 1316If 1317.Ev CDPATH 1318is unset, the current directory is searched. 1319The format of 1320.Ar CDPATH 1321is the same as that of 1322.Ev PATH . 1323In an interactive shell, 1324the 1325.Ic cd 1326command will print out the name of the directory 1327that it actually switched to 1328if this is different from the name that the user gave. 1329These may be different either because the 1330.Ev CDPATH 1331mechanism was used or because a symbolic link was crossed. 1332.Pp 1333If the 1334.Fl P 1335option is specified, 1336.Pa .. 1337is handled physically and symbolic links are resolved before 1338.Pa .. 1339components are processed. 1340If the 1341.Fl L 1342option is specified, 1343.Pa .. 1344is handled logically. 1345This is the default. 1346.It Ic chdir 1347A synonym for the 1348.Ic cd 1349built-in command. 1350.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 1351Execute the specified 1352.Ar utility 1353as a simple command (see the 1354.Sx Simple Commands 1355section). 1356.Pp 1357If the 1358.Fl p 1359option is specified, the command search is performed using a 1360default value of 1361.Ev PATH 1362that is guaranteed to find all of the standard utilities. 1363.It Ic echo Oo Fl e | n Oc Op Ar string 1364Print 1365.Ar string 1366to the standard output with a newline appended. 1367.Bl -tag -width indent 1368.It Fl n 1369Suppress the output of the trailing newline. 1370.It Fl e 1371Process C-style backslash escape sequences. 1372.Ic echo 1373understands the following character escapes: 1374.Bl -tag -width indent 1375.It \ea 1376Alert (ring the terminal bell) 1377.It \eb 1378Backspace 1379.It \ec 1380Suppress the trailing newline (this has the side-effect of truncating the 1381line if it is not the last character) 1382.It \ee 1383The ESC character (ASCII 0x1b) 1384.It \ef 1385Formfeed 1386.It \en 1387Newline 1388.It \er 1389Carriage return 1390.It \et 1391Horizontal tab 1392.It \ev 1393Vertical tab 1394.It \e\e 1395Literal backslash 1396.It \e0nnn 1397(Zero) The character whose octal value is nnn 1398.El 1399.Pp 1400If 1401.Ar string 1402is not enclosed in quotes then the backslash itself must be escaped 1403with a backslash to protect it from the shell. For example 1404.Bd -literal -offset indent 1405$ echo -e "a\evb" 1406a 1407 b 1408$ echo -e a\e\evb 1409a 1410 b 1411$ echo -e "a\e\eb" 1412a\eb 1413$ echo -e a\e\e\e\eb 1414a\eb 1415.Ed 1416.El 1417.Pp 1418Only one of the 1419.Fl e 1420and 1421.Fl n 1422options may be specified. 1423.It Ic eval Ar string ... 1424Concatenate all the arguments with spaces. 1425Then re-parse and execute the command. 1426.It Ic exec Op Ar command Op arg ... 1427Unless 1428.Ar command 1429is omitted, 1430the shell process is replaced with the specified program 1431(which must be a real program, not a shell built-in command or function). 1432Any redirections on the 1433.Ic exec 1434command are marked as permanent, 1435so that they are not undone when the 1436.Ic exec 1437command finishes. 1438.It Ic exit Op Ar exitstatus 1439Terminate the shell process. 1440If 1441.Ar exitstatus 1442is given 1443it is used as the exit status of the shell; 1444otherwise the exit status of the preceding command is used. 1445.It Ic export Oo Fl p Oc Op Ar name ... 1446The specified names are exported so that they will 1447appear in the environment of subsequent commands. 1448The only way to un-export a variable is to 1449.Ic unset 1450it. 1451The shell allows the value of a variable to be set 1452at the same time as it is exported by writing 1453.Bd -literal -offset indent 1454export name=value 1455.Ed 1456.Pp 1457With no arguments the export command lists the names 1458of all exported variables. 1459If the 1460.Fl p 1461option is specified, the exported variables are printed as 1462.Dq Ic export Ar name Ns = Ns Ar value 1463lines, suitable for re-input to the shell. 1464.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 1465.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 1466.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 1467The 1468.Ic fc 1469built-in command lists, or edits and re-executes, 1470commands previously entered to an interactive shell. 1471.Bl -tag -width indent 1472.It Fl e Ar editor 1473Use the editor named by 1474.Ar editor 1475to edit the commands. 1476The editor string is a command name, 1477subject to search via the 1478.Ev PATH 1479variable. 1480The value in the 1481.Ev FCEDIT 1482variable is used as a default when 1483.Fl e 1484is not specified. 1485If 1486.Ev FCEDIT 1487is null or unset, the value of the 1488.Ev EDITOR 1489variable is used. 1490If 1491.Ev EDITOR 1492is null or unset, 1493.Xr ed 1 1494is used as the editor. 1495.It Fl l No (ell) 1496List the commands rather than invoking 1497an editor on them. The commands are written in the 1498sequence indicated by the first and last operands, as 1499affected by 1500.Fl r , 1501with each command preceded by the command number. 1502.It Fl n 1503Suppress command numbers when listing with 1504.Fl l . 1505.It Fl r 1506Reverse the order of the commands listed 1507(with 1508.Fl l ) 1509or edited 1510(with neither 1511.Fl l 1512nor 1513.Fl s ) . 1514.It Fl s 1515Re-execute the command without invoking an editor. 1516.It Ar first 1517.It Ar last 1518Select the commands to list or edit. 1519The number of previous commands that can be accessed 1520are determined by the value of the 1521.Ev HISTSIZE 1522variable. 1523The value of 1524.Ar first 1525or 1526.Ar last 1527or both are one of the following: 1528.Bl -tag -width indent 1529.It Ar [+]num 1530A positive number representing a command number; 1531command numbers can be displayed with the 1532.Fl l 1533option. 1534.It Ar -num 1535A negative decimal number representing the 1536command that was executed 1537.Ar num 1538of 1539commands previously. 1540For example, -1 is the immediately previous command. 1541.It Ar string 1542A string indicating the most recently entered command 1543that begins with that string. 1544If the 1545.Ar old=new 1546operand is not also specified with 1547.Fl s , 1548the string form of the first operand cannot contain an embedded equal sign. 1549.El 1550.El 1551.Pp 1552The following environment variables affect the execution of 1553.Ic fc : 1554.Bl -tag -width indent 1555.It Ev FCEDIT 1556Name of the editor to use. 1557.It Ev HISTSIZE 1558The number of previous commands that are accessible. 1559.El 1560.It Ic fg Op Ar job 1561Move the specified 1562.Ar job 1563or the current job to the foreground. 1564.It Ic getopts Ar optstring Ar var 1565The POSIX 1566.Ic getopts 1567command. 1568The 1569.Ic getopts 1570command deprecates the older 1571.Xr getopt 1 1572command. 1573The first argument should be a series of letters, each possibly 1574followed by a colon which indicates that the option takes an argument. 1575The specified variable is set to the parsed option. The index of 1576the next argument is placed into the shell variable 1577.Ev OPTIND . 1578If an option takes an argument, it is placed into the shell variable 1579.Ev OPTARG . 1580If an invalid option is encountered, 1581.Ev var 1582is set to 1583.Dq Li \&? . 1584It returns a false value (1) when it encounters the end of the options. 1585.It Ic hash Oo Fl rv Oc Op Ar command ... 1586The shell maintains a hash table which remembers the locations of commands. 1587With no arguments whatsoever, the 1588.Ic hash 1589command prints out the contents of this table. 1590Entries which have not been looked at since the last 1591.Ic cd 1592command are marked with an asterisk; 1593it is possible for these entries to be invalid. 1594.Pp 1595With arguments, the 1596.Ic hash 1597command removes each specified 1598.Ar command 1599from the hash table (unless they are functions) and then locates it. 1600With the 1601.Fl v 1602option, 1603.Ic hash 1604prints the locations of the commands as it finds them. 1605The 1606.Fl r 1607option causes the 1608.Ic hash 1609command to delete all the entries in the hash table except for functions. 1610.It Ic jobid Op Ar job 1611Print the process id's of the processes in the specified 1612.Ar job . 1613If the 1614.Ar job 1615argument is omitted, use the current job. 1616.It Ic jobs Oo Fl ls Oc Op Ar job ... 1617Print information about the specified jobs, or all jobs if no 1618.Ar job 1619argument is given. 1620The information printed includes job ID, status and command name. 1621.Pp 1622If the 1623.Fl l 1624option is specified, the PID of each job is also printed. 1625If the 1626.Fl s 1627option is specified, only the PIDs of the jobs are printed, one per line. 1628.It Ic pwd Op Fl LP 1629Print the path of the current directory. The built-in command may 1630differ from the program of the same name because the 1631built-in command remembers what the current directory 1632is rather than recomputing it each time. This makes 1633it faster. However, if the current directory is 1634renamed, 1635the built-in version of 1636.Xr pwd 1 1637will continue to print the old name for the directory. 1638.Pp 1639If the 1640.Fl P 1641option is specified, symbolic links are resolved. 1642If the 1643.Fl L 1644option is specified, the shell's notion of the current directory 1645is printed (symbolic links are not resolved). 1646This is the default. 1647.It Ic read Oo Fl p Ar prompt Oc Oo Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 1648The 1649.Ar prompt 1650is printed if the 1651.Fl p 1652option is specified 1653and the standard input is a terminal. Then a line is 1654read from the standard input. The trailing newline 1655is deleted from the line and the line is split as 1656described in the section on 1657.Sx White Space Splitting (Field Splitting) 1658above, and 1659the pieces are assigned to the variables in order. 1660If there are more pieces than variables, the remaining 1661pieces (along with the characters in 1662.Ev IFS 1663that separated them) 1664are assigned to the last variable. 1665If there are more variables than pieces, the remaining 1666variables are assigned the null string. 1667.Pp 1668Backslashes are treated specially, unless the 1669.Fl r 1670option is 1671specified. If a backslash is followed by 1672a newline, the backslash and the newline will be 1673deleted. If a backslash is followed by any other 1674character, the backslash will be deleted and the following 1675character will be treated as though it were not in 1676.Ev IFS , 1677even if it is. 1678.Pp 1679If the 1680.Fl t 1681option is specified and the 1682.Ar timeout 1683elapses before any input is supplied, 1684the 1685.Ic read 1686command will return without assigning any values. 1687The 1688.Ar timeout 1689value may optionally be followed by one of 1690.Dq s , 1691.Dq m 1692or 1693.Dq h 1694to explicitly specify seconds, minutes or hours. 1695If none is supplied, 1696.Dq s 1697is assumed. 1698.Pp 1699The 1700.Fl e 1701option exists only for backward compatibility with older scripts. 1702.It Ic readonly Oo Fl p Oc Op Ar name ... 1703Each specified 1704.Ar name 1705is marked as read only, 1706so that it cannot be subsequently modified or unset. 1707The shell allows the value of a variable to be set 1708at the same time as it is marked read only 1709by using the following form: 1710.Bd -literal -offset indent 1711readonly name=value 1712.Ed 1713.Pp 1714With no arguments the 1715.Ic readonly 1716command lists the names of all read only variables. 1717If the 1718.Fl p 1719option is specified, the read-only variables are printed as 1720.Dq Ic readonly Ar name Ns = Ns Ar value 1721lines, suitable for re-input to the shell. 1722.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 1723.Fl c Ar string Oc Op Fl - Ar arg ... 1724The 1725.Ic set 1726command performs three different functions: 1727.Bl -item 1728.It 1729With no arguments, it lists the values of all shell variables. 1730.It 1731If options are given, 1732either in short form or using the long 1733.Dq Fl /+o Ar longname 1734form, 1735it sets or clears the specified options as described in the section called 1736.Sx Argument List Processing . 1737.It 1738If the 1739.Dq Fl - 1740option is specified, 1741.Ic set 1742will replace the shell's positional parameters with the subsequent 1743arguments. 1744If no arguments follow the 1745.Dq Fl - 1746option, 1747all the positional parameters will be cleared, 1748which is equivalent to executing the command 1749.Dq Li shift $# . 1750The 1751.Dq Fl - 1752flag may be omitted when specifying arguments to be used 1753as positional replacement parameters. 1754This is not recommended, 1755because the first argument may begin with a dash 1756.Pq Li - 1757or a plus 1758.Pq Li + , 1759which the 1760.Ic set 1761command will interpret as a request to enable or disable options. 1762.El 1763.It Ic setvar Ar variable Ar value 1764Assigns the specified 1765.Ar value 1766to the specified 1767.Ar variable . 1768.Ic Setvar 1769is intended to be used in functions that 1770assign values to variables whose names are passed as parameters. 1771In general it is better to write 1772.Bd -literal -offset indent 1773variable=value 1774.Ed 1775rather than using 1776.Ic setvar . 1777.It Ic shift Op Ar n 1778Shift the positional parameters 1779.Ar n 1780times, or once if 1781.Ar n 1782is not specified. 1783A shift sets the value of $1 to the value of $2, 1784the value of $2 to the value of $3, and so on, 1785decreasing the value of $# by one. 1786If there are zero positional parameters, shifting does not do anything. 1787.It Ic trap Oo Ar action Oc Ar signal ... 1788Cause the shell to parse and execute 1789.Ar action 1790when any specified 1791.Ar signal 1792is received. 1793The signals are specified by signal number. 1794The 1795.Ar action 1796may be null or omitted; 1797the former causes the specified signal to be ignored 1798and the latter causes the default action to be taken. 1799When the shell forks off a subshell, 1800it resets trapped (but not ignored) signals to the default action. 1801The 1802.Ic trap 1803command has no effect on signals that were ignored on entry to the shell. 1804.It Ic type Op Ar name ... 1805Interpret each 1806.Ar name 1807as a command and print the resolution of the command search. 1808Possible resolutions are: 1809shell keyword, alias, shell built-in command, command, tracked alias 1810and not found. 1811For aliases the alias expansion is printed; 1812for commands and tracked aliases 1813the complete pathname of the command is printed. 1814.It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit 1815Set or display resource limits (see 1816.Xr getrlimit 2 ) . 1817If 1818.Ar limit 1819is specified, the named resource will be set; 1820otherwise the current resource value will be displayed. 1821.Pp 1822If 1823.Fl H 1824is specified, the hard limits will be set or displayed. 1825While everybody is allowed to reduce a hard limit, 1826only the superuser can increase it. 1827The 1828.Fl S 1829option 1830specifies the soft limits instead. When displaying limits, 1831only one of 1832.Fl S 1833or 1834.Fl H 1835can be given. 1836The default is to display the soft limits, 1837and to set both the hard and the soft limits. 1838.Pp 1839Option 1840.Fl a 1841causes the 1842.Ic ulimit 1843command to display all resources. 1844The parameter 1845.Ar limit 1846is not acceptable in this mode. 1847.Pp 1848The remaining options specify which resource value is to be 1849displayed or modified. 1850They are mutually exclusive. 1851.Bl -tag -width indent 1852.It Fl b Ar sbsize 1853The maximum size of socket buffer usage, in bytes. 1854.It Fl c Ar coredumpsize 1855The maximal size of core dump files, in 512-byte blocks. 1856.It Fl d Ar datasize 1857The maximal size of the data segment of a process, in kilobytes. 1858.It Fl f Ar filesize 1859The maximal size of a file, in 512-byte blocks. 1860.It Fl l Ar lockedmem 1861The maximal size of memory that can be locked by a process, in 1862kilobytes. 1863.It Fl m Ar memoryuse 1864The maximal resident set size of a process, in kilobytes. 1865.It Fl n Ar nofiles 1866The maximal number of descriptors that could be opened by a process. 1867.It Fl s Ar stacksize 1868The maximal size of the stack segment, in kilobytes. 1869.It Fl t Ar time 1870The maximal amount of CPU time to be used by each process, in seconds. 1871.It Fl u Ar userproc 1872The maximal number of simultaneous processes for this user ID. 1873.It Fl v Ar virtualmem 1874The maximal virtual size of a process, in kilobytes. 1875.El 1876.It Ic umask Op Ar mask 1877Set the file creation mask (see 1878.Xr umask 2 ) 1879to the octal value specified by 1880.Ar mask . 1881If the argument is omitted, the current mask value is printed. 1882.It Ic unalias Oo Fl a Oc Op Ar name 1883If 1884.Ar name 1885is specified, the shell removes that alias. 1886If 1887.Fl a 1888is specified, all aliases are removed. 1889.It Ic unset Oo Fl fv Oc Ar name ... 1890The specified variables or functions are unset and unexported. 1891If the 1892.Fl v 1893option is specified or no options are given, the 1894.Ar name 1895arguments are treated as variable names. 1896If the 1897.Fl f 1898option is specified, the 1899.Ar name 1900arguments are treated as function names. 1901.It Ic wait Op Ar job 1902Wait for the specified 1903.Ar job 1904to complete and return the exit status of the last process in the 1905.Ar job . 1906If the argument is omitted, wait for all jobs to complete 1907and return an exit status of zero. 1908.El 1909.Ss Commandline Editing 1910When 1911.Nm 1912is being used interactively from a terminal, the current command 1913and the command history 1914(see 1915.Ic fc 1916in 1917.Sx Built-in Commands ) 1918can be edited using vi-mode command line editing. 1919This mode uses commands similar 1920to a subset of those described in the vi man page. 1921The command 1922.Dq Li set -o vi 1923(or 1924.Dq Li set -V ) 1925enables vi-mode editing and places 1926.Nm 1927into vi insert mode. With vi-mode enabled, 1928.Nm 1929can be switched between insert mode and command mode by typing 1930.Aq ESC . 1931Hitting 1932.Aq return 1933while in command mode will pass the line to the shell. 1934.Pp 1935Similarly, the 1936.Dq Li set -o emacs 1937(or 1938.Dq Li set -E ) 1939command can be used to enable a subset of 1940emacs-style command line editing features. 1941.Sh SEE ALSO 1942.Xr builtin 1 , 1943.Xr echo 1 , 1944.Xr expr 1 , 1945.Xr pwd 1 , 1946.Xr test 1 1947.Sh HISTORY 1948A 1949.Nm 1950command appeared in 1951.At v1 . 1952