1.\"- 2.\" Copyright (c) 1991, 1993 3.\" The Regents of the University of California. All rights reserved. 4.\" 5.\" This code is derived from software contributed to Berkeley by 6.\" Kenneth Almquist. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 33.\" $FreeBSD$ 34.\" 35.Dd January 20, 2013 36.Dt SH 1 37.Os 38.Sh NAME 39.Nm sh 40.Nd command interpreter (shell) 41.Sh SYNOPSIS 42.Nm 43.Op Fl /+abCEefIimnPpTuVvx 44.Op Fl /+o Ar longname 45.Oo 46.Ar script 47.Op Ar arg ... 48.Oc 49.Nm 50.Op Fl /+abCEefIimnPpTuVvx 51.Op Fl /+o Ar longname 52.Fl c Ar string 53.Oo 54.Ar name 55.Op Ar arg ... 56.Oc 57.Nm 58.Op Fl /+abCEefIimnPpTuVvx 59.Op Fl /+o Ar longname 60.Fl s 61.Op Ar arg ... 62.Sh DESCRIPTION 63The 64.Nm 65utility is the standard command interpreter for the system. 66The current version of 67.Nm 68is close to the 69.St -p1003.1 70specification for the shell. 71It only supports features 72designated by 73.Tn POSIX , 74plus a few Berkeley extensions. 75This man page is not intended to be a tutorial nor a complete 76specification of the shell. 77.Ss Overview 78The shell is a command that reads lines from 79either a file or the terminal, interprets them, and 80generally executes other commands. 81It is the program that is started when a user logs into the system, 82although a user can select a different shell with the 83.Xr chsh 1 84command. 85The shell 86implements a language that has flow control constructs, 87a macro facility that provides a variety of features in 88addition to data storage, along with built-in history and line 89editing capabilities. 90It incorporates many features to 91aid interactive use and has the advantage that the interpretative 92language is common to both interactive and non-interactive 93use (shell scripts). 94That is, commands can be typed directly 95to the running shell or can be put into a file, 96which can be executed directly by the shell. 97.Ss Invocation 98.\" 99.\" XXX This next sentence is incredibly confusing. 100.\" 101If no arguments are present and if the standard input of the shell 102is connected to a terminal 103(or if the 104.Fl i 105option is set), 106the shell is considered an interactive shell. 107An interactive shell 108generally prompts before each command and handles programming 109and command errors differently (as described below). 110When first starting, the shell inspects argument 0, and 111if it begins with a dash 112.Pq Ql - , 113the shell is also considered a login shell. 114This is normally done automatically by the system 115when the user first logs in. 116A login shell first reads commands 117from the files 118.Pa /etc/profile 119and then 120.Pa .profile 121in a user's home directory, 122if they exist. 123If the environment variable 124.Ev ENV 125is set on entry to a shell, or is set in the 126.Pa .profile 127of a login shell, the shell then subjects its value to parameter expansion 128and arithmetic expansion and reads commands from the named file. 129Therefore, a user should place commands that are to be executed only 130at login time in the 131.Pa .profile 132file, and commands that are executed for every shell inside the 133.Ev ENV 134file. 135The user can set the 136.Ev ENV 137variable to some file by placing the following line in the file 138.Pa .profile 139in the home directory, 140substituting for 141.Pa .shrc 142the filename desired: 143.Pp 144.Dl "ENV=$HOME/.shrc; export ENV" 145.Pp 146The first non-option argument specified on the command line 147will be treated as the 148name of a file from which to read commands (a shell script), and 149the remaining arguments are set as the positional parameters 150of the shell 151.Li ( $1 , $2 , 152etc.). 153Otherwise, the shell reads commands 154from its standard input. 155.Pp 156Unlike older versions of 157.Nm 158the 159.Ev ENV 160script is only sourced on invocation of interactive shells. 161This 162closes a well-known, and sometimes easily exploitable security 163hole related to poorly thought out 164.Ev ENV 165scripts. 166.Ss Argument List Processing 167All of the single letter options to 168.Nm 169have a corresponding long name, 170with the exception of 171.Fl c 172and 173.Fl /+o . 174These long names are provided next to the single letter options 175in the descriptions below. 176The long name for an option may be specified as an argument to the 177.Fl /+o 178option of 179.Nm . 180Once the shell is running, 181the long name for an option may be specified as an argument to the 182.Fl /+o 183option of the 184.Ic set 185built-in command 186(described later in the section called 187.Sx Built-in Commands ) . 188Introducing an option with a dash 189.Pq Ql - 190enables the option, 191while using a plus 192.Pq Ql + 193disables the option. 194A 195.Dq Li -- 196or plain 197.Ql - 198will stop option processing and will force the remaining 199words on the command line to be treated as arguments. 200The 201.Fl /+o 202and 203.Fl c 204options do not have long names. 205They take arguments and are described after the single letter options. 206.Bl -tag -width indent 207.It Fl a Li allexport 208Flag variables for export when assignments are made to them. 209.It Fl b Li notify 210Enable asynchronous notification of background job 211completion. 212(UNIMPLEMENTED) 213.It Fl C Li noclobber 214Do not overwrite existing files with 215.Ql > . 216.It Fl E Li emacs 217Enable the built-in 218.Xr emacs 1 219command line editor (disables the 220.Fl V 221option if it has been set; 222set automatically when interactive on terminals). 223.It Fl e Li errexit 224Exit immediately if any untested command fails in non-interactive mode. 225The exit status of a command is considered to be 226explicitly tested if the command is part of the list used to control 227an 228.Ic if , elif , while , 229or 230.Ic until ; 231if the command is the left 232hand operand of an 233.Dq Li && 234or 235.Dq Li || 236operator; or if the command is a pipeline preceded by the 237.Ic !\& 238operator. 239If a shell function is executed and its exit status is explicitly 240tested, all commands of the function are considered to be tested as 241well. 242.It Fl f Li noglob 243Disable pathname expansion. 244.It Fl h Li trackall 245A do-nothing option for 246.Tn POSIX 247compliance. 248.It Fl I Li ignoreeof 249Ignore 250.Dv EOF Ap s 251from input when in interactive mode. 252.It Fl i Li interactive 253Force the shell to behave interactively. 254.It Fl m Li monitor 255Turn on job control (set automatically when interactive). 256.It Fl n Li noexec 257If not interactive, read commands but do not 258execute them. 259This is useful for checking the 260syntax of shell scripts. 261.It Fl P Li physical 262Change the default for the 263.Ic cd 264and 265.Ic pwd 266commands from 267.Fl L 268(logical directory layout) 269to 270.Fl P 271(physical directory layout). 272.It Fl p Li privileged 273Turn on privileged mode. 274This mode is enabled on startup 275if either the effective user or group ID is not equal to the 276real user or group ID. 277Turning this mode off sets the 278effective user and group IDs to the real user and group IDs. 279When this mode is enabled for interactive shells, the file 280.Pa /etc/suid_profile 281is sourced instead of 282.Pa ~/.profile 283after 284.Pa /etc/profile 285is sourced, and the contents of the 286.Ev ENV 287variable are ignored. 288.It Fl s Li stdin 289Read commands from standard input (set automatically 290if no file arguments are present). 291This option has 292no effect when set after the shell has already started 293running (i.e., when set with the 294.Ic set 295command). 296.It Fl T Li trapsasync 297When waiting for a child, execute traps immediately. 298If this option is not set, 299traps are executed after the child exits, 300as specified in 301.St -p1003.2 . 302This nonstandard option is useful for putting guarding shells around 303children that block signals. 304The surrounding shell may kill the child 305or it may just return control to the tty and leave the child alone, 306like this: 307.Bd -literal -offset indent 308sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 309.Ed 310.It Fl u Li nounset 311Write a message to standard error when attempting 312to expand a variable, a positional parameter or 313the special parameter 314.Va \&! 315that is not set, and if the 316shell is not interactive, exit immediately. 317.It Fl V Li vi 318Enable the built-in 319.Xr vi 1 320command line editor (disables 321.Fl E 322if it has been set). 323.It Fl v Li verbose 324The shell writes its input to standard error 325as it is read. 326Useful for debugging. 327.It Fl x Li xtrace 328Write each command 329(preceded by the value of the 330.Va PS4 331variable subjected to parameter expansion and arithmetic expansion) 332to standard error before it is executed. 333Useful for debugging. 334.El 335.Pp 336The 337.Fl c 338option causes the commands to be read from the 339.Ar string 340operand instead of from the standard input. 341Keep in mind that this option only accepts a single string as its 342argument, hence multi-word strings must be quoted. 343.Pp 344The 345.Fl /+o 346option takes as its only argument the long name of an option 347to be enabled or disabled. 348For example, the following two invocations of 349.Nm 350both enable the built-in 351.Xr emacs 1 352command line editor: 353.Bd -literal -offset indent 354set -E 355set -o emacs 356.Ed 357.Pp 358If used without an argument, the 359.Fl o 360option displays the current option settings in a human-readable format. 361If 362.Cm +o 363is used without an argument, the current option settings are output 364in a format suitable for re-input into the shell. 365.Ss Lexical Structure 366The shell reads input in terms of lines from a file and breaks 367it up into words at whitespace (blanks and tabs), and at 368certain sequences of 369characters called 370.Dq operators , 371which are special to the shell. 372There are two types of operators: control operators and 373redirection operators (their meaning is discussed later). 374The following is a list of valid operators: 375.Bl -tag -width indent 376.It Control operators: 377.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 378.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en 379.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li || 380.El 381.It Redirection operators: 382.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 383.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 384.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \& 385.El 386.El 387.Pp 388The character 389.Ql # 390introduces a comment if used at the beginning of a word. 391The word starting with 392.Ql # 393and the rest of the line are ignored. 394.Pp 395.Tn ASCII 396.Dv NUL 397characters (character code 0) are not allowed in shell input. 398.Ss Quoting 399Quoting is used to remove the special meaning of certain characters 400or words to the shell, such as operators, whitespace, keywords, 401or alias names. 402.Pp 403There are four types of quoting: matched single quotes, 404dollar-single quotes, 405matched double quotes, and backslash. 406.Bl -tag -width indent 407.It Single Quotes 408Enclosing characters in single quotes preserves the literal 409meaning of all the characters (except single quotes, making 410it impossible to put single-quotes in a single-quoted string). 411.It Dollar-Single Quotes 412Enclosing characters between 413.Li $' 414and 415.Li ' 416preserves the literal meaning of all characters 417except backslashes and single quotes. 418A backslash introduces a C-style escape sequence: 419.Bl -tag -width xUnnnnnnnn 420.It \ea 421Alert (ring the terminal bell) 422.It \eb 423Backspace 424.It \ec Ns Ar c 425The control character denoted by 426.Li ^ Ns Ar c 427in 428.Xr stty 1 . 429If 430.Ar c 431is a backslash, it must be doubled. 432.It \ee 433The ESC character 434.Tn ( ASCII 4350x1b) 436.It \ef 437Formfeed 438.It \en 439Newline 440.It \er 441Carriage return 442.It \et 443Horizontal tab 444.It \ev 445Vertical tab 446.It \e\e 447Literal backslash 448.It \e\&' 449Literal single-quote 450.It \e\&" 451Literal double-quote 452.It \e Ns Ar nnn 453The byte whose octal value is 454.Ar nnn 455(one to three digits) 456.It \ex Ns Ar nn 457The byte whose hexadecimal value is 458.Ar nn 459(one or more digits only the last two of which are used) 460.It \eu Ns Ar nnnn 461The Unicode code point 462.Ar nnnn 463(four hexadecimal digits) 464.It \eU Ns Ar nnnnnnnn 465The Unicode code point 466.Ar nnnnnnnn 467(eight hexadecimal digits) 468.El 469.Pp 470The sequences for Unicode code points are currently only useful with 471UTF-8 locales. 472They reject code point 0 and UTF-16 surrogates. 473.Pp 474If an escape sequence would produce a byte with value 0, 475that byte and the rest of the string until the matching single-quote 476are ignored. 477.Pp 478Any other string starting with a backslash is an error. 479.It Double Quotes 480Enclosing characters within double quotes preserves the literal 481meaning of all characters except dollar sign 482.Pq Ql $ , 483backquote 484.Pq Ql ` , 485and backslash 486.Pq Ql \e . 487The backslash inside double quotes is historically weird. 488It remains literal unless it precedes the following characters, 489which it serves to quote: 490.Pp 491.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 492.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en 493.El 494.It Backslash 495A backslash preserves the literal meaning of the following 496character, with the exception of the newline character 497.Pq Ql \en . 498A backslash preceding a newline is treated as a line continuation. 499.El 500.Ss Keywords 501Keywords or reserved words are words that have special meaning to the 502shell and are recognized at the beginning of a line and 503after a control operator. 504The following are keywords: 505.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 506.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 507.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 508.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 509.El 510.Ss Aliases 511An alias is a name and corresponding value set using the 512.Ic alias 513built-in command. 514Wherever the command word of a simple command may occur, 515and after checking for keywords if a keyword may occur, the shell 516checks the word to see if it matches an alias. 517If it does, it replaces it in the input stream with its value. 518For example, if there is an alias called 519.Dq Li lf 520with the value 521.Dq Li "ls -F" , 522then the input 523.Pp 524.Dl "lf foobar" 525.Pp 526would become 527.Pp 528.Dl "ls -F foobar" 529.Pp 530Aliases provide a convenient way for naive users to 531create shorthands for commands without having to learn how 532to create functions with arguments. 533Using aliases in scripts is discouraged 534because the command that defines them must be executed 535before the code that uses them is parsed. 536This is fragile and not portable. 537.Pp 538An alias name may be escaped in a command line, so that it is not 539replaced by its alias value, by using quoting characters within or 540adjacent to the alias name. 541This is most often done by prefixing 542an alias name with a backslash to execute a function, built-in, or 543normal program with the same name. 544See the 545.Sx Quoting 546subsection. 547.Ss Commands 548The shell interprets the words it reads according to a 549language, the specification of which is outside the scope 550of this man page (refer to the BNF in the 551.St -p1003.2 552document). 553Essentially though, a line is read and if 554the first word of the line (or after a control operator) 555is not a keyword, then the shell has recognized a 556simple command. 557Otherwise, a complex command or some 558other special construct may have been recognized. 559.Ss Simple Commands 560If a simple command has been recognized, the shell performs 561the following actions: 562.Bl -enum 563.It 564Leading words of the form 565.Dq Li name=value 566are stripped off and assigned to the environment of 567the simple command. 568Redirection operators and 569their arguments (as described below) are stripped 570off and saved for processing. 571.It 572The remaining words are expanded as described in 573the section called 574.Sx Word Expansions , 575and the first remaining word is considered the command 576name and the command is located. 577The remaining 578words are considered the arguments of the command. 579If no command name resulted, then the 580.Dq Li name=value 581variable assignments recognized in 1) affect the 582current shell. 583.It 584Redirections are performed as described in 585the next section. 586.El 587.Ss Redirections 588Redirections are used to change where a command reads its input 589or sends its output. 590In general, redirections open, close, or 591duplicate an existing reference to a file. 592The overall format 593used for redirection is: 594.Pp 595.D1 Oo Ar n Oc Ar redir-op file 596.Pp 597The 598.Ar redir-op 599is one of the redirection operators mentioned 600previously. 601The following gives some examples of how these 602operators can be used. 603Note that stdin and stdout are commonly used abbreviations 604for standard input and standard output respectively. 605.Bl -tag -width "1234567890XX" -offset indent 606.It Oo Ar n Oc Ns Li > Ar file 607redirect stdout (or file descriptor 608.Ar n ) 609to 610.Ar file 611.It Oo Ar n Oc Ns Li >| Ar file 612same as above, but override the 613.Fl C 614option 615.It Oo Ar n Oc Ns Li >> Ar file 616append stdout (or file descriptor 617.Ar n ) 618to 619.Ar file 620.It Oo Ar n Oc Ns Li < Ar file 621redirect stdin (or file descriptor 622.Ar n ) 623from 624.Ar file 625.It Oo Ar n Oc Ns Li <> Ar file 626redirect stdin (or file descriptor 627.Ar n ) 628to and from 629.Ar file 630.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 631duplicate stdin (or file descriptor 632.Ar n1 ) 633from file descriptor 634.Ar n2 635.It Oo Ar n Oc Ns Li <&- 636close stdin (or file descriptor 637.Ar n ) 638.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 639duplicate stdout (or file descriptor 640.Ar n1 ) 641to file descriptor 642.Ar n2 643.It Oo Ar n Oc Ns Li >&- 644close stdout (or file descriptor 645.Ar n ) 646.El 647.Pp 648The following redirection is often called a 649.Dq here-document . 650.Bd -unfilled -offset indent 651.Oo Ar n Oc Ns Li << Ar delimiter 652.Ar here-doc-text 653.Ar ... 654.Ar delimiter 655.Ed 656.Pp 657All the text on successive lines up to the delimiter is 658saved away and made available to the command on standard 659input, or file descriptor 660.Ar n 661if it is specified. 662If the 663.Ar delimiter 664as specified on the initial line is quoted, then the 665.Ar here-doc-text 666is treated literally, otherwise the text is subjected to 667parameter expansion, command substitution, and arithmetic 668expansion (as described in the section on 669.Sx Word Expansions ) . 670If the operator is 671.Dq Li <<- 672instead of 673.Dq Li << , 674then leading tabs 675in the 676.Ar here-doc-text 677are stripped. 678.Ss Search and Execution 679There are three types of commands: shell functions, 680built-in commands, and normal programs. 681The command is searched for (by name) in that order. 682The three types of commands are all executed in a different way. 683.Pp 684When a shell function is executed, all of the shell positional 685parameters (except 686.Li $0 , 687which remains unchanged) are 688set to the arguments of the shell function. 689The variables which are explicitly placed in the environment of 690the command (by placing assignments to them before the 691function name) are made local to the function and are set 692to the values given. 693Then the command given in the function definition is executed. 694The positional parameters are restored to their original values 695when the command completes. 696This all occurs within the current shell. 697.Pp 698Shell built-in commands are executed internally to the shell, without 699spawning a new process. 700There are two kinds of built-in commands: regular and special. 701Assignments before special builtins persist after they finish 702executing and assignment errors, redirection errors and certain 703operand errors cause a script to be aborted. 704Special builtins cannot be overridden with a function. 705Both regular and special builtins can affect the shell in ways 706normal programs cannot. 707.Pp 708Otherwise, if the command name does not match a function 709or built-in command, the command is searched for as a normal 710program in the file system (as described in the next section). 711When a normal program is executed, the shell runs the program, 712passing the arguments and the environment to the program. 713If the program is not a normal executable file 714(i.e., if it does not begin with the 715.Dq "magic number" 716whose 717.Tn ASCII 718representation is 719.Dq Li #! , 720resulting in an 721.Er ENOEXEC 722return value from 723.Xr execve 2 ) 724but appears to be a text file, 725the shell will run a new instance of 726.Nm 727to interpret it. 728.Pp 729Note that previous versions of this document 730and the source code itself misleadingly and sporadically 731refer to a shell script without a magic number 732as a 733.Dq "shell procedure" . 734.Ss Path Search 735When locating a command, the shell first looks to see if 736it has a shell function by that name. 737Then it looks for a 738built-in command by that name. 739If a built-in command is not found, 740one of two things happen: 741.Bl -enum 742.It 743Command names containing a slash are simply executed without 744performing any searches. 745.It 746The shell searches each entry in the 747.Va PATH 748variable 749in turn for the command. 750The value of the 751.Va PATH 752variable should be a series of 753entries separated by colons. 754Each entry consists of a 755directory name. 756The current directory 757may be indicated implicitly by an empty directory name, 758or explicitly by a single period. 759.El 760.Ss Command Exit Status 761Each command has an exit status that can influence the behavior 762of other shell commands. 763The paradigm is that a command exits 764with zero for normal or success, and non-zero for failure, 765error, or a false indication. 766The man page for each command 767should indicate the various exit codes and what they mean. 768Additionally, the built-in commands return exit codes, as does 769an executed shell function. 770.Pp 771If a command is terminated by a signal, its exit status is 128 plus 772the signal number. 773Signal numbers are defined in the header file 774.In sys/signal.h . 775.Ss Complex Commands 776Complex commands are combinations of simple commands 777with control operators or keywords, together creating a larger complex 778command. 779More generally, a command is one of the following: 780.Bl -item -offset indent 781.It 782simple command 783.It 784pipeline 785.It 786list or compound-list 787.It 788compound command 789.It 790function definition 791.El 792.Pp 793Unless otherwise stated, the exit status of a command is 794that of the last simple command executed by the command. 795.Ss Pipelines 796A pipeline is a sequence of one or more commands separated 797by the control operator 798.Ql \&| . 799The standard output of all but 800the last command is connected to the standard input 801of the next command. 802The standard output of the last 803command is inherited from the shell, as usual. 804.Pp 805The format for a pipeline is: 806.Pp 807.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... 808.Pp 809The standard output of 810.Ar command1 811is connected to the standard input of 812.Ar command2 . 813The standard input, standard output, or 814both of a command is considered to be assigned by the 815pipeline before any redirection specified by redirection 816operators that are part of the command. 817.Pp 818Note that unlike some other shells, 819.Nm 820executes each process in a pipeline with more than one command 821in a subshell environment and as a child of the 822.Nm 823process. 824.Pp 825If the pipeline is not in the background (discussed later), 826the shell waits for all commands to complete. 827.Pp 828If the keyword 829.Ic !\& 830does not precede the pipeline, the 831exit status is the exit status of the last command specified 832in the pipeline. 833Otherwise, the exit status is the logical 834NOT of the exit status of the last command. 835That is, if 836the last command returns zero, the exit status is 1; if 837the last command returns greater than zero, the exit status 838is zero. 839.Pp 840Because pipeline assignment of standard input or standard 841output or both takes place before redirection, it can be 842modified by redirection. 843For example: 844.Pp 845.Dl "command1 2>&1 | command2" 846.Pp 847sends both the standard output and standard error of 848.Ar command1 849to the standard input of 850.Ar command2 . 851.Pp 852A 853.Ql \&; 854or newline terminator causes the preceding 855AND-OR-list 856(described below in the section called 857.Sx Short-Circuit List Operators ) 858to be executed sequentially; 859an 860.Ql & 861causes asynchronous execution of the preceding AND-OR-list. 862.Ss Background Commands (&) 863If a command is terminated by the control operator ampersand 864.Pq Ql & , 865the shell executes the command in a subshell environment (see 866.Sx Grouping Commands Together 867below) and asynchronously; 868the shell does not wait for the command to finish 869before executing the next command. 870.Pp 871The format for running a command in background is: 872.Pp 873.D1 Ar command1 Li & Op Ar command2 Li & Ar ... 874.Pp 875If the shell is not interactive, the standard input of an 876asynchronous command is set to 877.Pa /dev/null . 878.Ss Lists (Generally Speaking) 879A list is a sequence of zero or more commands separated by 880newlines, semicolons, or ampersands, 881and optionally terminated by one of these three characters. 882The commands in a 883list are executed in the order they are written. 884If command is followed by an ampersand, the shell starts the 885command and immediately proceeds onto the next command; 886otherwise it waits for the command to terminate before 887proceeding to the next one. 888.Ss Short-Circuit List Operators 889.Dq Li && 890and 891.Dq Li || 892are AND-OR list operators. 893.Dq Li && 894executes the first command, and then executes the second command 895if the exit status of the first command is zero. 896.Dq Li || 897is similar, but executes the second command if the exit 898status of the first command is nonzero. 899.Dq Li && 900and 901.Dq Li || 902both have the same priority. 903.Ss Flow-Control Constructs (if, while, for, case) 904The syntax of the 905.Ic if 906command is: 907.Bd -unfilled -offset indent -compact 908.Ic if Ar list 909.Ic then Ar list 910.Oo Ic elif Ar list 911.Ic then Ar list Oc Ar ... 912.Op Ic else Ar list 913.Ic fi 914.Ed 915.Pp 916The syntax of the 917.Ic while 918command is: 919.Bd -unfilled -offset indent -compact 920.Ic while Ar list 921.Ic do Ar list 922.Ic done 923.Ed 924.Pp 925The two lists are executed repeatedly while the exit status of the 926first list is zero. 927The 928.Ic until 929command is similar, but has the word 930.Ic until 931in place of 932.Ic while , 933which causes it to 934repeat until the exit status of the first list is zero. 935.Pp 936The syntax of the 937.Ic for 938command is: 939.Bd -unfilled -offset indent -compact 940.Ic for Ar variable Op Ic in Ar word ... 941.Ic do Ar list 942.Ic done 943.Ed 944.Pp 945If 946.Ic in 947and the following words are omitted, 948.Ic in Li \&"$@\&" 949is used instead. 950The words are expanded, and then the list is executed 951repeatedly with the variable set to each word in turn. 952The 953.Ic do 954and 955.Ic done 956commands may be replaced with 957.Ql { 958and 959.Ql } . 960.Pp 961The syntax of the 962.Ic break 963and 964.Ic continue 965commands is: 966.D1 Ic break Op Ar num 967.D1 Ic continue Op Ar num 968.Pp 969The 970.Ic break 971command terminates the 972.Ar num 973innermost 974.Ic for 975or 976.Ic while 977loops. 978The 979.Ic continue 980command continues with the next iteration of the innermost loop. 981These are implemented as special built-in commands. 982.Pp 983The syntax of the 984.Ic case 985command is: 986.Bd -unfilled -offset indent -compact 987.Ic case Ar word Ic in 988.Ar pattern Ns Li ) Ar list Li ;; 989.Ar ... 990.Ic esac 991.Ed 992.Pp 993The pattern can actually be one or more patterns 994(see 995.Sx Shell Patterns 996described later), 997separated by 998.Ql \&| 999characters. 1000Tilde expansion, parameter expansion, command substitution, 1001arithmetic expansion and quote removal are applied to the word. 1002Then, each pattern is expanded in turn using tilde expansion, 1003parameter expansion, command substitution and arithmetic expansion and 1004the expanded form of the word is checked against it. 1005If a match is found, the corresponding list is executed. 1006If the selected list is terminated by the control operator 1007.Ql ;& 1008instead of 1009.Ql ;; , 1010execution continues with the next list, 1011continuing until a list terminated with 1012.Ql ;; 1013or the end of the 1014.Ic case 1015command. 1016The exit code of the 1017.Ic case 1018command is the exit code of the last command executed in the list or 1019zero if no patterns were matched. 1020.Ss Grouping Commands Together 1021Commands may be grouped by writing either 1022.Pp 1023.D1 Li \&( Ns Ar list Ns Li \%) 1024.Pp 1025or 1026.Pp 1027.D1 Li { Ar list Ns Li \&; } 1028.Pp 1029The first form executes the commands in a subshell environment. 1030A subshell environment has its own copy of: 1031.Bl -enum 1032.It 1033The current working directory as set by 1034.Ic cd . 1035.It 1036The file creation mask as set by 1037.Ic umask . 1038.It 1039References to open files. 1040.It 1041Traps as set by 1042.Ic trap . 1043.It 1044Known jobs. 1045.It 1046Positional parameters and variables. 1047.It 1048Shell options. 1049.It 1050Shell functions. 1051.It 1052Shell aliases. 1053.El 1054.Pp 1055These are copied from the parent shell environment, 1056except that trapped (but not ignored) signals are reset to the default action 1057and known jobs are cleared. 1058Any changes do not affect the parent shell environment. 1059.Pp 1060A subshell environment may be implemented as a child process or differently. 1061If job control is enabled in an interactive shell, 1062commands grouped in parentheses can be suspended and continued as a unit. 1063.Pp 1064The second form never forks another shell, 1065so it is slightly more efficient. 1066Grouping commands together this way allows the user to 1067redirect their output as though they were one program: 1068.Bd -literal -offset indent 1069{ echo -n "hello"; echo " world"; } > greeting 1070.Ed 1071.Ss Functions 1072The syntax of a function definition is 1073.Pp 1074.D1 Ar name Li \&( \&) Ar command 1075.Pp 1076A function definition is an executable statement; when 1077executed it installs a function named 1078.Ar name 1079and returns an 1080exit status of zero. 1081The 1082.Ar command 1083is normally a list 1084enclosed between 1085.Ql { 1086and 1087.Ql } . 1088.Pp 1089Variables may be declared to be local to a function by 1090using the 1091.Ic local 1092command. 1093This should appear as the first statement of a function, 1094and the syntax is: 1095.Pp 1096.D1 Ic local Oo Ar variable ... Oc Op Fl 1097.Pp 1098The 1099.Ic local 1100command is implemented as a built-in command. 1101.Pp 1102When a variable is made local, it inherits the initial 1103value and exported and readonly flags from the variable 1104with the same name in the surrounding scope, if there is 1105one. 1106Otherwise, the variable is initially unset. 1107The shell 1108uses dynamic scoping, so that if the variable 1109.Va x 1110is made local to function 1111.Em f , 1112which then calls function 1113.Em g , 1114references to the variable 1115.Va x 1116made inside 1117.Em g 1118will refer to the variable 1119.Va x 1120declared inside 1121.Em f , 1122not to the global variable named 1123.Va x . 1124.Pp 1125The only special parameter that can be made local is 1126.Ql - . 1127Making 1128.Ql - 1129local causes any shell options that are 1130changed via the 1131.Ic set 1132command inside the function to be 1133restored to their original values when the function 1134returns. 1135.Pp 1136The syntax of the 1137.Ic return 1138command is 1139.Pp 1140.D1 Ic return Op Ar exitstatus 1141.Pp 1142It terminates the current executional scope, returning from the previous 1143nested function, sourced script, or shell instance, in that order. 1144The 1145.Ic return 1146command is implemented as a special built-in command. 1147.Ss Variables and Parameters 1148The shell maintains a set of parameters. 1149A parameter 1150denoted by a name is called a variable. 1151When starting up, 1152the shell turns all the environment variables into shell 1153variables. 1154New variables can be set using the form 1155.Pp 1156.D1 Ar name Ns = Ns Ar value 1157.Pp 1158Variables set by the user must have a name consisting solely 1159of alphabetics, numerics, and underscores. 1160The first letter of a variable name must not be numeric. 1161A parameter can also be denoted by a number 1162or a special character as explained below. 1163.Pp 1164Assignments are expanded differently from other words: 1165tilde expansion is also performed after the equals sign and after any colon 1166and usernames are also terminated by colons, 1167and field splitting and pathname expansion are not performed. 1168.Pp 1169This special expansion applies not only to assignments that form a simple 1170command by themselves or precede a command word, 1171but also to words passed to the 1172.Ic export , 1173.Ic local 1174or 1175.Ic readonly 1176built-in commands that have this form. 1177For this, the builtin's name must be literal 1178(not the result of an expansion) 1179and may optionally be preceded by one or more literal instances of 1180.Ic command 1181without options. 1182.Ss Positional Parameters 1183A positional parameter is a parameter denoted by a number greater than zero. 1184The shell sets these initially to the values of its command line 1185arguments that follow the name of the shell script. 1186The 1187.Ic set 1188built-in command can also be used to set or reset them. 1189.Ss Special Parameters 1190Special parameters are parameters denoted by a single special character 1191or the digit zero. 1192They are shown in the following list, exactly as they would appear in input 1193typed by the user or in the source of a shell script. 1194.Bl -hang 1195.It Li $* 1196Expands to the positional parameters, starting from one. 1197When 1198the expansion occurs within a double-quoted string 1199it expands to a single field with the value of each parameter 1200separated by the first character of the 1201.Va IFS 1202variable, 1203or by a space if 1204.Va IFS 1205is unset. 1206.It Li $@ 1207Expands to the positional parameters, starting from one. 1208When 1209the expansion occurs within double-quotes, each positional 1210parameter expands as a separate argument. 1211If there are no positional parameters, the 1212expansion of 1213.Li @ 1214generates zero arguments, even when 1215.Li @ 1216is double-quoted. 1217What this basically means, for example, is 1218if 1219.Li $1 1220is 1221.Dq Li abc 1222and 1223.Li $2 1224is 1225.Dq Li "def ghi" , 1226then 1227.Li \&"$@\&" 1228expands to 1229the two arguments: 1230.Bd -literal -offset indent 1231"abc" "def ghi" 1232.Ed 1233.It Li $# 1234Expands to the number of positional parameters. 1235.It Li $? 1236Expands to the exit status of the most recent pipeline. 1237.It Li $- 1238(hyphen) Expands to the current option flags (the single-letter 1239option names concatenated into a string) as specified on 1240invocation, by the 1241.Ic set 1242built-in command, or implicitly 1243by the shell. 1244.It Li $$ 1245Expands to the process ID of the invoked shell. 1246A subshell 1247retains the same value of 1248.Va $ 1249as its parent. 1250.It Li $! 1251Expands to the process ID of the most recent background 1252command executed from the current shell. 1253For a 1254pipeline, the process ID is that of the last command in the 1255pipeline. 1256If this parameter is referenced, the shell will remember 1257the process ID and its exit status until the 1258.Ic wait 1259built-in command reports completion of the process. 1260.It Li $0 1261(zero) Expands to the name of the shell script if passed on the command line, 1262the 1263.Ar name 1264operand if given (with 1265.Fl c ) 1266or otherwise argument 0 passed to the shell. 1267.El 1268.Ss Special Variables 1269The following variables are set by the shell or 1270have special meaning to it: 1271.Bl -tag -width ".Va HISTSIZE" 1272.It Va CDPATH 1273The search path used with the 1274.Ic cd 1275built-in. 1276.It Va EDITOR 1277The fallback editor used with the 1278.Ic fc 1279built-in. 1280If not set, the default editor is 1281.Xr ed 1 . 1282.It Va FCEDIT 1283The default editor used with the 1284.Ic fc 1285built-in. 1286.It Va HISTSIZE 1287The number of previous commands that are accessible. 1288.It Va HOME 1289The user's home directory, 1290used in tilde expansion and as a default directory for the 1291.Ic cd 1292built-in. 1293.It Va IFS 1294Input Field Separators. 1295The default value is 1296.Aq space , 1297.Aq tab , 1298and 1299.Aq newline 1300in that order. 1301This default also applies if 1302.Va IFS 1303is unset, but not if it is set to the empty string. 1304See the 1305.Sx White Space Splitting 1306section for more details. 1307.It Va LINENO 1308The current line number in the script or function. 1309.It Va MAIL 1310The name of a mail file, that will be checked for the arrival of new 1311mail. 1312Overridden by 1313.Va MAILPATH . 1314.It Va MAILPATH 1315A colon 1316.Pq Ql \&: 1317separated list of file names, for the shell to check for incoming 1318mail. 1319This variable overrides the 1320.Va MAIL 1321setting. 1322There is a maximum of 10 mailboxes that can be monitored at once. 1323.It Va PATH 1324The default search path for executables. 1325See the 1326.Sx Path Search 1327section for details. 1328.It Va PPID 1329The parent process ID of the invoked shell. 1330This is set at startup 1331unless this variable is in the environment. 1332A later change of parent process ID is not reflected. 1333A subshell retains the same value of 1334.Va PPID . 1335.It Va PS1 1336The primary prompt string, which defaults to 1337.Dq Li "$ " , 1338unless you are the superuser, in which case it defaults to 1339.Dq Li "# " . 1340.It Va PS2 1341The secondary prompt string, which defaults to 1342.Dq Li "> " . 1343.It Va PS4 1344The prefix for the trace output (if 1345.Fl x 1346is active). 1347The default is 1348.Dq Li "+ " . 1349.El 1350.Ss Word Expansions 1351This clause describes the various expansions that are 1352performed on words. 1353Not all expansions are performed on 1354every word, as explained later. 1355.Pp 1356Tilde expansions, parameter expansions, command substitutions, 1357arithmetic expansions, and quote removals that occur within 1358a single word expand to a single field. 1359It is only field 1360splitting or pathname expansion that can create multiple 1361fields from a single word. 1362The single exception to this rule is 1363the expansion of the special parameter 1364.Va @ 1365within double-quotes, 1366as was described above. 1367.Pp 1368The order of word expansion is: 1369.Bl -enum 1370.It 1371Tilde Expansion, Parameter Expansion, Command Substitution, 1372Arithmetic Expansion (these all occur at the same time). 1373.It 1374Field Splitting is performed on fields generated by step (1) 1375unless the 1376.Va IFS 1377variable is null. 1378.It 1379Pathname Expansion (unless the 1380.Fl f 1381option is in effect). 1382.It 1383Quote Removal. 1384.El 1385.Pp 1386The 1387.Ql $ 1388character is used to introduce parameter expansion, command 1389substitution, or arithmetic expansion. 1390.Ss Tilde Expansion (substituting a user's home directory) 1391A word beginning with an unquoted tilde character 1392.Pq Ql ~ 1393is 1394subjected to tilde expansion. 1395All the characters up to a slash 1396.Pq Ql / 1397or the end of the word are treated as a username 1398and are replaced with the user's home directory. 1399If the 1400username is missing (as in 1401.Pa ~/foobar ) , 1402the tilde is replaced with the value of the 1403.Va HOME 1404variable (the current user's home directory). 1405.Ss Parameter Expansion 1406The format for parameter expansion is as follows: 1407.Pp 1408.D1 Li ${ Ns Ar expression Ns Li } 1409.Pp 1410where 1411.Ar expression 1412consists of all characters until the matching 1413.Ql } . 1414Any 1415.Ql } 1416escaped by a backslash or within a single-quoted or double-quoted 1417string, and characters in 1418embedded arithmetic expansions, command substitutions, and variable 1419expansions, are not examined in determining the matching 1420.Ql } . 1421If the variants with 1422.Ql + , 1423.Ql - , 1424.Ql = 1425or 1426.Ql ?\& 1427occur within a double-quoted string, 1428as an extension there may be unquoted parts 1429(via double-quotes inside the expansion); 1430.Ql } 1431within such parts are also not examined in determining the matching 1432.Ql } . 1433.Pp 1434The simplest form for parameter expansion is: 1435.Pp 1436.D1 Li ${ Ns Ar parameter Ns Li } 1437.Pp 1438The value, if any, of 1439.Ar parameter 1440is substituted. 1441.Pp 1442The parameter name or symbol can be enclosed in braces, which are 1443optional except for positional parameters with more than one digit or 1444when parameter is followed by a character that could be interpreted as 1445part of the name. 1446If a parameter expansion occurs inside double-quotes: 1447.Bl -enum 1448.It 1449Field splitting is not performed on the results of the 1450expansion, with the exception of the special parameter 1451.Va @ . 1452.It 1453Pathname expansion is not performed on the results of the 1454expansion. 1455.El 1456.Pp 1457In addition, a parameter expansion can be modified by using one of the 1458following formats. 1459.Bl -tag -width indent 1460.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1461Use Default Values. 1462If 1463.Ar parameter 1464is unset or null, the expansion of 1465.Ar word 1466is substituted; otherwise, the value of 1467.Ar parameter 1468is substituted. 1469.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1470Assign Default Values. 1471If 1472.Ar parameter 1473is unset or null, the expansion of 1474.Ar word 1475is assigned to 1476.Ar parameter . 1477In all cases, the 1478final value of 1479.Ar parameter 1480is substituted. 1481Quoting inside 1482.Ar word 1483does not prevent field splitting or pathname expansion. 1484Only variables, not positional 1485parameters or special parameters, can be 1486assigned in this way. 1487.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1488Indicate Error if Null or Unset. 1489If 1490.Ar parameter 1491is unset or null, the expansion of 1492.Ar word 1493(or a message indicating it is unset if 1494.Ar word 1495is omitted) is written to standard 1496error and the shell exits with a nonzero 1497exit status. 1498Otherwise, the value of 1499.Ar parameter 1500is substituted. 1501An 1502interactive shell need not exit. 1503.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1504Use Alternate Value. 1505If 1506.Ar parameter 1507is unset or null, null is substituted; 1508otherwise, the expansion of 1509.Ar word 1510is substituted. 1511.El 1512.Pp 1513In the parameter expansions shown previously, use of the colon in the 1514format results in a test for a parameter that is unset or null; omission 1515of the colon results in a test for a parameter that is only unset. 1516.Pp 1517The 1518.Ar word 1519inherits the type of quoting 1520(unquoted, double-quoted or here-document) 1521from the surroundings, 1522with the exception that a backslash that quotes a closing brace is removed 1523during quote removal. 1524.Bl -tag -width indent 1525.It Li ${# Ns Ar parameter Ns Li } 1526String Length. 1527The length in characters of 1528the value of 1529.Ar parameter . 1530.El 1531.Pp 1532The following four varieties of parameter expansion provide for substring 1533processing. 1534In each case, pattern matching notation 1535(see 1536.Sx Shell Patterns ) , 1537rather than regular expression notation, 1538is used to evaluate the patterns. 1539If parameter is one of the special parameters 1540.Va * 1541or 1542.Va @ , 1543the result of the expansion is unspecified. 1544Enclosing the full parameter expansion string in double-quotes does not 1545cause the following four varieties of pattern characters to be quoted, 1546whereas quoting characters within the braces has this effect. 1547.Bl -tag -width indent 1548.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1549Remove Smallest Suffix Pattern. 1550The 1551.Ar word 1552is expanded to produce a pattern. 1553The 1554parameter expansion then results in 1555.Ar parameter , 1556with the smallest portion of the 1557suffix matched by the pattern deleted. 1558.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1559Remove Largest Suffix Pattern. 1560The 1561.Ar word 1562is expanded to produce a pattern. 1563The 1564parameter expansion then results in 1565.Ar parameter , 1566with the largest portion of the 1567suffix matched by the pattern deleted. 1568.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1569Remove Smallest Prefix Pattern. 1570The 1571.Ar word 1572is expanded to produce a pattern. 1573The 1574parameter expansion then results in 1575.Ar parameter , 1576with the smallest portion of the 1577prefix matched by the pattern deleted. 1578.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1579Remove Largest Prefix Pattern. 1580The 1581.Ar word 1582is expanded to produce a pattern. 1583The 1584parameter expansion then results in 1585.Ar parameter , 1586with the largest portion of the 1587prefix matched by the pattern deleted. 1588.El 1589.Ss Command Substitution 1590Command substitution allows the output of a command to be substituted in 1591place of the command name itself. 1592Command substitution occurs when 1593the command is enclosed as follows: 1594.Pp 1595.D1 Li $( Ns Ar command Ns Li )\& 1596.Pp 1597or the backquoted version: 1598.Pp 1599.D1 Li ` Ns Ar command Ns Li ` 1600.Pp 1601The shell expands the command substitution by executing command 1602and replacing the command substitution 1603with the standard output of the command, 1604removing sequences of one or more newlines at the end of the substitution. 1605Embedded newlines before the end of the output are not removed; 1606however, during field splitting, they may be translated into spaces 1607depending on the value of 1608.Va IFS 1609and the quoting that is in effect. 1610The command is executed in a subshell environment, 1611except that the built-in commands 1612.Ic jobid , 1613.Ic jobs , 1614and 1615.Ic trap 1616return information about the parent shell environment 1617and 1618.Ic times 1619returns information about the same process 1620if they are the only command in a command substitution. 1621.Ss Arithmetic Expansion 1622Arithmetic expansion provides a mechanism for evaluating an arithmetic 1623expression and substituting its value. 1624The format for arithmetic expansion is as follows: 1625.Pp 1626.D1 Li $(( Ns Ar expression Ns Li )) 1627.Pp 1628The 1629.Ar expression 1630is treated as if it were in double-quotes, except 1631that a double-quote inside the expression is not treated specially. 1632The 1633shell expands all tokens in the 1634.Ar expression 1635for parameter expansion, 1636command substitution, 1637arithmetic expansion 1638and quote removal. 1639.Pp 1640The allowed expressions are a subset of C expressions, 1641summarized below. 1642.Bl -tag -width "Variables" -offset indent 1643.It Values 1644All values are of type 1645.Ft intmax_t . 1646.It Constants 1647Decimal, octal (starting with 1648.Li 0 ) 1649and hexadecimal (starting with 1650.Li 0x ) 1651integer constants. 1652.It Variables 1653Shell variables can be read and written 1654and contain integer constants. 1655.It Unary operators 1656.Li "! ~ + -" 1657.It Binary operators 1658.Li "* / % + - << >> < <= > >= == != & ^ | && ||" 1659.It Assignment operators 1660.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1661.It Conditional operator 1662.Li "? :" 1663.El 1664.Pp 1665The result of the expression is substituted in decimal. 1666.Ss White Space Splitting (Field Splitting) 1667In certain contexts, 1668after parameter expansion, command substitution, and 1669arithmetic expansion the shell scans the results of 1670expansions and substitutions that did not occur in double-quotes for 1671field splitting and multiple fields can result. 1672.Pp 1673Characters in 1674.Va IFS 1675that are whitespace 1676.Po 1677.Aq space , 1678.Aq tab , 1679and 1680.Aq newline 1681.Pc 1682are treated differently from other characters in 1683.Va IFS . 1684.Pp 1685Whitespace in 1686.Va IFS 1687at the beginning or end of a word is discarded. 1688.Pp 1689Subsequently, a field is delimited by either 1690.Bl -enum 1691.It 1692a non-whitespace character in 1693.Va IFS 1694with any whitespace in 1695.Va IFS 1696surrounding it, or 1697.It 1698one or more whitespace characters in 1699.Va IFS . 1700.El 1701.Pp 1702If a word ends with a non-whitespace character in 1703.Va IFS , 1704there is no empty field after this character. 1705.Pp 1706If no field is delimited, the word is discarded. 1707In particular, if a word consists solely of an unquoted substitution 1708and the result of the substitution is null, 1709it is removed by field splitting even if 1710.Va IFS 1711is null. 1712.Ss Pathname Expansion (File Name Generation) 1713Unless the 1714.Fl f 1715option is set, 1716file name generation is performed 1717after word splitting is complete. 1718Each word is 1719viewed as a series of patterns, separated by slashes. 1720The 1721process of expansion replaces the word with the names of 1722all existing files whose names can be formed by replacing 1723each pattern with a string that matches the specified pattern. 1724There are two restrictions on this: first, a pattern cannot match 1725a string containing a slash, and second, 1726a pattern cannot match a string starting with a period 1727unless the first character of the pattern is a period. 1728The next section describes the patterns used for 1729Pathname Expansion, 1730the four varieties of parameter expansion for substring processing and the 1731.Ic case 1732command. 1733.Ss Shell Patterns 1734A pattern consists of normal characters, which match themselves, 1735and meta-characters. 1736The meta-characters are 1737.Ql * , 1738.Ql \&? , 1739and 1740.Ql \&[ . 1741These characters lose their special meanings if they are quoted. 1742When command or variable substitution is performed and the dollar sign 1743or back quotes are not double-quoted, the value of the 1744variable or the output of the command is scanned for these 1745characters and they are turned into meta-characters. 1746.Pp 1747An asterisk 1748.Pq Ql * 1749matches any string of characters. 1750A question mark 1751.Pq Ql \&? 1752matches any single character. 1753A left bracket 1754.Pq Ql \&[ 1755introduces a character class. 1756The end of the character class is indicated by a 1757.Ql \&] ; 1758if the 1759.Ql \&] 1760is missing then the 1761.Ql \&[ 1762matches a 1763.Ql \&[ 1764rather than introducing a character class. 1765A character class matches any of the characters between the square brackets. 1766A locale-dependent range of characters may be specified using a minus sign. 1767A named class of characters (see 1768.Xr wctype 3 ) 1769may be specified by surrounding the name with 1770.Ql \&[: 1771and 1772.Ql :\&] . 1773For example, 1774.Ql \&[\&[:alpha:\&]\&] 1775is a shell pattern that matches a single letter. 1776The character class may be complemented by making an exclamation point 1777.Pq Ql !\& 1778the first character of the character class. 1779A caret 1780.Pq Ql ^ 1781has the same effect but is non-standard. 1782.Pp 1783To include a 1784.Ql \&] 1785in a character class, make it the first character listed 1786(after the 1787.Ql \&! 1788or 1789.Ql ^ , 1790if any). 1791To include a 1792.Ql - , 1793make it the first or last character listed. 1794.Ss Built-in Commands 1795This section lists the built-in commands. 1796.Bl -tag -width indent 1797.It Ic \&: 1798A null command that returns a 0 (true) exit value. 1799.It Ic \&. Ar file 1800The commands in the specified file are read and executed by the shell. 1801The 1802.Ic return 1803command may be used to return to the 1804.Ic \&. 1805command's caller. 1806If 1807.Ar file 1808contains any 1809.Ql / 1810characters, it is used as is. 1811Otherwise, the shell searches the 1812.Va PATH 1813for the file. 1814If it is not found in the 1815.Va PATH , 1816it is sought in the current working directory. 1817.It Ic \&[ 1818A built-in equivalent of 1819.Xr test 1 . 1820.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc 1821If 1822.Ar name Ns = Ns Ar string 1823is specified, the shell defines the alias 1824.Ar name 1825with value 1826.Ar string . 1827If just 1828.Ar name 1829is specified, the value of the alias 1830.Ar name 1831is printed. 1832With no arguments, the 1833.Ic alias 1834built-in command prints the names and values of all defined aliases 1835(see 1836.Ic unalias ) . 1837Alias values are written with appropriate quoting so that they are 1838suitable for re-input to the shell. 1839Also see the 1840.Sx Aliases 1841subsection. 1842.It Ic bg Op Ar job ... 1843Continue the specified jobs 1844(or the current job if no jobs are given) 1845in the background. 1846.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1847List or alter key bindings for the line editor. 1848This command is documented in 1849.Xr editrc 5 . 1850.It Ic break Op Ar num 1851See the 1852.Sx Flow-Control Constructs 1853subsection. 1854.It Ic builtin Ar cmd Op Ar arg ... 1855Execute the specified built-in command, 1856.Ar cmd . 1857This is useful when the user wishes to override a shell function 1858with the same name as a built-in command. 1859.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 1860Switch to the specified 1861.Ar directory , 1862or to the directory specified in the 1863.Va HOME 1864environment variable if no 1865.Ar directory 1866is specified. 1867If 1868.Ar directory 1869does not begin with 1870.Pa / , \&. , 1871or 1872.Pa .. , 1873then the directories listed in the 1874.Va CDPATH 1875variable will be 1876searched for the specified 1877.Ar directory . 1878If 1879.Va CDPATH 1880is unset, the current directory is searched. 1881The format of 1882.Va CDPATH 1883is the same as that of 1884.Va PATH . 1885In an interactive shell, 1886the 1887.Ic cd 1888command will print out the name of the directory 1889that it actually switched to 1890if this is different from the name that the user gave. 1891These may be different either because the 1892.Va CDPATH 1893mechanism was used or because a symbolic link was crossed. 1894.Pp 1895If the 1896.Fl P 1897option is specified, 1898.Pa .. 1899is handled physically and symbolic links are resolved before 1900.Pa .. 1901components are processed. 1902If the 1903.Fl L 1904option is specified, 1905.Pa .. 1906is handled logically. 1907This is the default. 1908.Pp 1909The 1910.Fl e 1911option causes 1912.Ic cd 1913to return exit status 1 if the full pathname of the new directory 1914cannot be determined reliably or at all. 1915Normally this is not considered an error, 1916although a warning is printed. 1917.It Ic chdir 1918A synonym for the 1919.Ic cd 1920built-in command. 1921.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 1922.It Ic command Oo Fl p Oc Fl v Ar utility 1923.It Ic command Oo Fl p Oc Fl V Ar utility 1924The first form of invocation executes the specified 1925.Ar utility , 1926ignoring shell functions in the search. 1927If 1928.Ar utility 1929is a special builtin, 1930it is executed as if it were a regular builtin. 1931.Pp 1932If the 1933.Fl p 1934option is specified, the command search is performed using a 1935default value of 1936.Va PATH 1937that is guaranteed to find all of the standard utilities. 1938.Pp 1939If the 1940.Fl v 1941option is specified, 1942.Ar utility 1943is not executed but a description of its interpretation by the shell is 1944printed. 1945For ordinary commands the output is the path name; for shell built-in 1946commands, shell functions and keywords only the name is written. 1947Aliases are printed as 1948.Dq Ic alias Ar name Ns = Ns Ar value . 1949.Pp 1950The 1951.Fl V 1952option is identical to 1953.Fl v 1954except for the output. 1955It prints 1956.Dq Ar utility Ic is Ar description 1957where 1958.Ar description 1959is either 1960the path name to 1961.Ar utility , 1962a special shell builtin, 1963a shell builtin, 1964a shell function, 1965a shell keyword 1966or 1967an alias for 1968.Ar value . 1969.It Ic continue Op Ar num 1970See the 1971.Sx Flow-Control Constructs 1972subsection. 1973.It Ic echo Oo Fl e | n Oc Op Ar string ... 1974Print a space-separated list of the arguments to the standard output 1975and append a newline character. 1976.Bl -tag -width indent 1977.It Fl n 1978Suppress the output of the trailing newline. 1979.It Fl e 1980Process C-style backslash escape sequences. 1981The 1982.Ic echo 1983command understands the following character escapes: 1984.Bl -tag -width indent 1985.It \ea 1986Alert (ring the terminal bell) 1987.It \eb 1988Backspace 1989.It \ec 1990Suppress the trailing newline (this has the side-effect of truncating the 1991line if it is not the last character) 1992.It \ee 1993The ESC character 1994.Tn ( ASCII 19950x1b) 1996.It \ef 1997Formfeed 1998.It \en 1999Newline 2000.It \er 2001Carriage return 2002.It \et 2003Horizontal tab 2004.It \ev 2005Vertical tab 2006.It \e\e 2007Literal backslash 2008.It \e0nnn 2009(Zero) The character whose octal value is 2010.Ar nnn 2011.El 2012.Pp 2013If 2014.Ar string 2015is not enclosed in quotes then the backslash itself must be escaped 2016with a backslash to protect it from the shell. 2017For example 2018.Bd -literal -offset indent 2019$ echo -e "a\evb" 2020a 2021 b 2022$ echo -e a\e\evb 2023a 2024 b 2025$ echo -e "a\e\eb" 2026a\eb 2027$ echo -e a\e\e\e\eb 2028a\eb 2029.Ed 2030.El 2031.Pp 2032Only one of the 2033.Fl e 2034and 2035.Fl n 2036options may be specified. 2037.It Ic eval Ar string ... 2038Concatenate all the arguments with spaces. 2039Then re-parse and execute the command. 2040.It Ic exec Op Ar command Op arg ... 2041Unless 2042.Ar command 2043is omitted, 2044the shell process is replaced with the specified program 2045(which must be a real program, not a shell built-in command or function). 2046Any redirections on the 2047.Ic exec 2048command are marked as permanent, 2049so that they are not undone when the 2050.Ic exec 2051command finishes. 2052.It Ic exit Op Ar exitstatus 2053Terminate the shell process. 2054If 2055.Ar exitstatus 2056is given 2057it is used as the exit status of the shell. 2058Otherwise, if the shell is executing an 2059.Cm EXIT 2060trap, the exit status of the last command before the trap is used; 2061if the shell is executing a trap for a signal, 2062the shell exits by resending the signal to itself. 2063Otherwise, the exit status of the preceding command is used. 2064The exit status should be an integer between 0 and 255. 2065.It Ic export Ar name ... 2066.It Ic export Op Fl p 2067The specified names are exported so that they will 2068appear in the environment of subsequent commands. 2069The only way to un-export a variable is to 2070.Ic unset 2071it. 2072The shell allows the value of a variable to be set 2073at the same time as it is exported by writing 2074.Pp 2075.D1 Ic export Ar name Ns = Ns Ar value 2076.Pp 2077With no arguments the 2078.Ic export 2079command lists the names 2080of all exported variables. 2081If the 2082.Fl p 2083option is specified, the exported variables are printed as 2084.Dq Ic export Ar name Ns = Ns Ar value 2085lines, suitable for re-input to the shell. 2086.It Ic false 2087A null command that returns a non-zero (false) exit value. 2088.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2089.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2090.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2091The 2092.Ic fc 2093built-in command lists, or edits and re-executes, 2094commands previously entered to an interactive shell. 2095.Bl -tag -width indent 2096.It Fl e Ar editor 2097Use the editor named by 2098.Ar editor 2099to edit the commands. 2100The 2101.Ar editor 2102string is a command name, 2103subject to search via the 2104.Va PATH 2105variable. 2106The value in the 2107.Va FCEDIT 2108variable is used as a default when 2109.Fl e 2110is not specified. 2111If 2112.Va FCEDIT 2113is null or unset, the value of the 2114.Va EDITOR 2115variable is used. 2116If 2117.Va EDITOR 2118is null or unset, 2119.Xr ed 1 2120is used as the editor. 2121.It Fl l No (ell) 2122List the commands rather than invoking 2123an editor on them. 2124The commands are written in the 2125sequence indicated by the 2126.Ar first 2127and 2128.Ar last 2129operands, as affected by 2130.Fl r , 2131with each command preceded by the command number. 2132.It Fl n 2133Suppress command numbers when listing with 2134.Fl l . 2135.It Fl r 2136Reverse the order of the commands listed 2137(with 2138.Fl l ) 2139or edited 2140(with neither 2141.Fl l 2142nor 2143.Fl s ) . 2144.It Fl s 2145Re-execute the command without invoking an editor. 2146.It Ar first 2147.It Ar last 2148Select the commands to list or edit. 2149The number of previous commands that can be accessed 2150are determined by the value of the 2151.Va HISTSIZE 2152variable. 2153The value of 2154.Ar first 2155or 2156.Ar last 2157or both are one of the following: 2158.Bl -tag -width indent 2159.It Oo Cm + Oc Ns Ar num 2160A positive number representing a command number; 2161command numbers can be displayed with the 2162.Fl l 2163option. 2164.It Fl Ar num 2165A negative decimal number representing the 2166command that was executed 2167.Ar num 2168of 2169commands previously. 2170For example, \-1 is the immediately previous command. 2171.It Ar string 2172A string indicating the most recently entered command 2173that begins with that string. 2174If the 2175.Ar old Ns = Ns Ar new 2176operand is not also specified with 2177.Fl s , 2178the string form of the first operand cannot contain an embedded equal sign. 2179.El 2180.El 2181.Pp 2182The following variables affect the execution of 2183.Ic fc : 2184.Bl -tag -width ".Va HISTSIZE" 2185.It Va FCEDIT 2186Name of the editor to use for history editing. 2187.It Va HISTSIZE 2188The number of previous commands that are accessible. 2189.El 2190.It Ic fg Op Ar job 2191Move the specified 2192.Ar job 2193or the current job to the foreground. 2194.It Ic getopts Ar optstring var 2195The 2196.Tn POSIX 2197.Ic getopts 2198command. 2199The 2200.Ic getopts 2201command deprecates the older 2202.Xr getopt 1 2203command. 2204The first argument should be a series of letters, each possibly 2205followed by a colon which indicates that the option takes an argument. 2206The specified variable is set to the parsed option. 2207The index of 2208the next argument is placed into the shell variable 2209.Va OPTIND . 2210If an option takes an argument, it is placed into the shell variable 2211.Va OPTARG . 2212If an invalid option is encountered, 2213.Ar var 2214is set to 2215.Ql \&? . 2216It returns a false value (1) when it encounters the end of the options. 2217.It Ic hash Oo Fl rv Oc Op Ar command ... 2218The shell maintains a hash table which remembers the locations of commands. 2219With no arguments whatsoever, the 2220.Ic hash 2221command prints out the contents of this table. 2222.Pp 2223With arguments, the 2224.Ic hash 2225command removes each specified 2226.Ar command 2227from the hash table (unless they are functions) and then locates it. 2228With the 2229.Fl v 2230option, 2231.Ic hash 2232prints the locations of the commands as it finds them. 2233The 2234.Fl r 2235option causes the 2236.Ic hash 2237command to delete all the entries in the hash table except for functions. 2238.It Ic jobid Op Ar job 2239Print the process IDs of the processes in the specified 2240.Ar job . 2241If the 2242.Ar job 2243argument is omitted, use the current job. 2244.It Ic jobs Oo Fl lps Oc Op Ar job ... 2245Print information about the specified jobs, or all jobs if no 2246.Ar job 2247argument is given. 2248The information printed includes job ID, status and command name. 2249.Pp 2250If the 2251.Fl l 2252option is specified, the PID of each job is also printed. 2253If the 2254.Fl p 2255option is specified, only the process IDs for the process group leaders 2256are printed, one per line. 2257If the 2258.Fl s 2259option is specified, only the PIDs of the job commands are printed, one per 2260line. 2261.It Ic kill 2262A built-in equivalent of 2263.Xr kill 1 2264that additionally supports sending signals to jobs. 2265.It Ic local Oo Ar variable ... Oc Op Fl 2266See the 2267.Sx Functions 2268subsection. 2269.It Ic printf 2270A built-in equivalent of 2271.Xr printf 1 . 2272.It Ic pwd Op Fl L | P 2273Print the path of the current directory. 2274The built-in command may 2275differ from the program of the same name because the 2276built-in command remembers what the current directory 2277is rather than recomputing it each time. 2278This makes 2279it faster. 2280However, if the current directory is 2281renamed, 2282the built-in version of 2283.Xr pwd 1 2284will continue to print the old name for the directory. 2285.Pp 2286If the 2287.Fl P 2288option is specified, symbolic links are resolved. 2289If the 2290.Fl L 2291option is specified, the shell's notion of the current directory 2292is printed (symbolic links are not resolved). 2293This is the default. 2294.It Ic read Oo Fl p Ar prompt Oc Oo 2295.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2296The 2297.Ar prompt 2298is printed if the 2299.Fl p 2300option is specified 2301and the standard input is a terminal. 2302Then a line is 2303read from the standard input. 2304The trailing newline 2305is deleted from the line and the line is split as 2306described in the section on 2307.Sx White Space Splitting (Field Splitting) 2308above, and 2309the pieces are assigned to the variables in order. 2310If there are more pieces than variables, the remaining 2311pieces (along with the characters in 2312.Va IFS 2313that separated them) 2314are assigned to the last variable. 2315If there are more variables than pieces, the remaining 2316variables are assigned the null string. 2317.Pp 2318Backslashes are treated specially, unless the 2319.Fl r 2320option is 2321specified. 2322If a backslash is followed by 2323a newline, the backslash and the newline will be 2324deleted. 2325If a backslash is followed by any other 2326character, the backslash will be deleted and the following 2327character will be treated as though it were not in 2328.Va IFS , 2329even if it is. 2330.Pp 2331If the 2332.Fl t 2333option is specified and the 2334.Ar timeout 2335elapses before a complete line of input is supplied, 2336the 2337.Ic read 2338command will return an exit status of 1 without assigning any values. 2339The 2340.Ar timeout 2341value may optionally be followed by one of 2342.Ql s , 2343.Ql m 2344or 2345.Ql h 2346to explicitly specify seconds, minutes or hours. 2347If none is supplied, 2348.Ql s 2349is assumed. 2350.Pp 2351The 2352.Fl e 2353option exists only for backward compatibility with older scripts. 2354.It Ic readonly Oo Fl p Oc Op Ar name ... 2355Each specified 2356.Ar name 2357is marked as read only, 2358so that it cannot be subsequently modified or unset. 2359The shell allows the value of a variable to be set 2360at the same time as it is marked read only 2361by using the following form: 2362.Pp 2363.D1 Ic readonly Ar name Ns = Ns Ar value 2364.Pp 2365With no arguments the 2366.Ic readonly 2367command lists the names of all read only variables. 2368If the 2369.Fl p 2370option is specified, the read-only variables are printed as 2371.Dq Ic readonly Ar name Ns = Ns Ar value 2372lines, suitable for re-input to the shell. 2373.It Ic return Op Ar exitstatus 2374See the 2375.Sx Functions 2376subsection. 2377.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 2378.Fl c Ar string Oc Op Fl - Ar arg ... 2379The 2380.Ic set 2381command performs three different functions: 2382.Bl -item 2383.It 2384With no arguments, it lists the values of all shell variables. 2385.It 2386If options are given, 2387either in short form or using the long 2388.Dq Fl /+o Ar longname 2389form, 2390it sets or clears the specified options as described in the section called 2391.Sx Argument List Processing . 2392.It 2393If the 2394.Dq Fl - 2395option is specified, 2396.Ic set 2397will replace the shell's positional parameters with the subsequent 2398arguments. 2399If no arguments follow the 2400.Dq Fl - 2401option, 2402all the positional parameters will be cleared, 2403which is equivalent to executing the command 2404.Dq Li "shift $#" . 2405The 2406.Dq Fl - 2407flag may be omitted when specifying arguments to be used 2408as positional replacement parameters. 2409This is not recommended, 2410because the first argument may begin with a dash 2411.Pq Ql - 2412or a plus 2413.Pq Ql + , 2414which the 2415.Ic set 2416command will interpret as a request to enable or disable options. 2417.El 2418.It Ic setvar Ar variable value 2419Assigns the specified 2420.Ar value 2421to the specified 2422.Ar variable . 2423The 2424.Ic setvar 2425command is intended to be used in functions that 2426assign values to variables whose names are passed as parameters. 2427In general it is better to write 2428.Dq Ar variable Ns = Ns Ar value 2429rather than using 2430.Ic setvar . 2431.It Ic shift Op Ar n 2432Shift the positional parameters 2433.Ar n 2434times, or once if 2435.Ar n 2436is not specified. 2437A shift sets the value of 2438.Li $1 2439to the value of 2440.Li $2 , 2441the value of 2442.Li $2 2443to the value of 2444.Li $3 , 2445and so on, 2446decreasing the value of 2447.Li $# 2448by one. 2449If there are zero positional parameters, shifting does not do anything. 2450.It Ic test 2451A built-in equivalent of 2452.Xr test 1 . 2453.It Ic times 2454Print the amount of time spent executing the shell process and its children. 2455The first output line shows the user and system times for the shell process 2456itself, the second one contains the user and system times for the 2457children. 2458.It Ic trap Oo Ar action Oc Ar signal ... 2459.It Ic trap Fl l 2460Cause the shell to parse and execute 2461.Ar action 2462when any specified 2463.Ar signal 2464is received. 2465The signals are specified by name or number. 2466In addition, the pseudo-signal 2467.Cm EXIT 2468may be used to specify an 2469.Ar action 2470that is performed when the shell terminates. 2471The 2472.Ar action 2473may be an empty string or a dash 2474.Pq Ql - ; 2475the former causes the specified signal to be ignored 2476and the latter causes the default action to be taken. 2477Omitting the 2478.Ar action 2479is another way to request the default action, for compatibility reasons this 2480usage is not recommended though. 2481In a subshell or utility environment, 2482the shell resets trapped (but not ignored) signals to the default action. 2483The 2484.Ic trap 2485command has no effect on signals that were ignored on entry to the shell. 2486.Pp 2487Option 2488.Fl l 2489causes the 2490.Ic trap 2491command to display a list of valid signal names. 2492.It Ic true 2493A null command that returns a 0 (true) exit value. 2494.It Ic type Op Ar name ... 2495Interpret each 2496.Ar name 2497as a command and print the resolution of the command search. 2498Possible resolutions are: 2499shell keyword, alias, special shell builtin, shell builtin, command, 2500tracked alias 2501and not found. 2502For aliases the alias expansion is printed; 2503for commands and tracked aliases 2504the complete pathname of the command is printed. 2505.It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit 2506Set or display resource limits (see 2507.Xr getrlimit 2 ) . 2508If 2509.Ar limit 2510is specified, the named resource will be set; 2511otherwise the current resource value will be displayed. 2512.Pp 2513If 2514.Fl H 2515is specified, the hard limits will be set or displayed. 2516While everybody is allowed to reduce a hard limit, 2517only the superuser can increase it. 2518The 2519.Fl S 2520option 2521specifies the soft limits instead. 2522When displaying limits, 2523only one of 2524.Fl S 2525or 2526.Fl H 2527can be given. 2528The default is to display the soft limits, 2529and to set both the hard and the soft limits. 2530.Pp 2531Option 2532.Fl a 2533causes the 2534.Ic ulimit 2535command to display all resources. 2536The parameter 2537.Ar limit 2538is not acceptable in this mode. 2539.Pp 2540The remaining options specify which resource value is to be 2541displayed or modified. 2542They are mutually exclusive. 2543.Bl -tag -width indent 2544.It Fl b Ar sbsize 2545The maximum size of socket buffer usage, in bytes. 2546.It Fl c Ar coredumpsize 2547The maximal size of core dump files, in 512-byte blocks. 2548.It Fl d Ar datasize 2549The maximal size of the data segment of a process, in kilobytes. 2550.It Fl f Ar filesize 2551The maximal size of a file, in 512-byte blocks. 2552.It Fl l Ar lockedmem 2553The maximal size of memory that can be locked by a process, in 2554kilobytes. 2555.It Fl m Ar memoryuse 2556The maximal resident set size of a process, in kilobytes. 2557.It Fl n Ar nofiles 2558The maximal number of descriptors that could be opened by a process. 2559.It Fl p Ar pseudoterminals 2560The maximal number of pseudo-terminals for this user ID. 2561.It Fl s Ar stacksize 2562The maximal size of the stack segment, in kilobytes. 2563.It Fl t Ar time 2564The maximal amount of CPU time to be used by each process, in seconds. 2565.It Fl u Ar userproc 2566The maximal number of simultaneous processes for this user ID. 2567.It Fl v Ar virtualmem 2568The maximal virtual size of a process, in kilobytes. 2569.It Fl w Ar swapuse 2570The maximum amount of swap space reserved or used for this user ID, 2571in kilobytes. 2572.El 2573.It Ic umask Oo Fl S Oc Op Ar mask 2574Set the file creation mask (see 2575.Xr umask 2 ) 2576to the octal or symbolic (see 2577.Xr chmod 1 ) 2578value specified by 2579.Ar mask . 2580If the argument is omitted, the current mask value is printed. 2581If the 2582.Fl S 2583option is specified, the output is symbolic, otherwise the output is octal. 2584.It Ic unalias Oo Fl a Oc Op Ar name ... 2585The specified alias names are removed. 2586If 2587.Fl a 2588is specified, all aliases are removed. 2589.It Ic unset Oo Fl fv Oc Ar name ... 2590The specified variables or functions are unset and unexported. 2591If the 2592.Fl v 2593option is specified or no options are given, the 2594.Ar name 2595arguments are treated as variable names. 2596If the 2597.Fl f 2598option is specified, the 2599.Ar name 2600arguments are treated as function names. 2601.It Ic wait Op Ar job 2602Wait for the specified 2603.Ar job 2604to complete and return the exit status of the last process in the 2605.Ar job . 2606If the argument is omitted, wait for all jobs to complete 2607and return an exit status of zero. 2608.El 2609.Ss Commandline Editing 2610When 2611.Nm 2612is being used interactively from a terminal, the current command 2613and the command history 2614(see 2615.Ic fc 2616in 2617.Sx Built-in Commands ) 2618can be edited using 2619.Nm vi Ns -mode 2620command line editing. 2621This mode uses commands similar 2622to a subset of those described in the 2623.Xr vi 1 2624man page. 2625The command 2626.Dq Li "set -o vi" 2627(or 2628.Dq Li "set -V" ) 2629enables 2630.Nm vi Ns -mode 2631editing and places 2632.Nm 2633into 2634.Nm vi 2635insert mode. 2636With 2637.Nm vi Ns -mode 2638enabled, 2639.Nm 2640can be switched between insert mode and command mode by typing 2641.Aq ESC . 2642Hitting 2643.Aq return 2644while in command mode will pass the line to the shell. 2645.Pp 2646Similarly, the 2647.Dq Li "set -o emacs" 2648(or 2649.Dq Li "set -E" ) 2650command can be used to enable a subset of 2651.Nm emacs Ns -style 2652command line editing features. 2653.Sh ENVIRONMENT 2654The following environment variables affect the execution of 2655.Nm : 2656.Bl -tag -width ".Ev LANGXXXXXX" 2657.It Ev ENV 2658Initialization file for interactive shells. 2659.It Ev LANG , Ev LC_* 2660Locale settings. 2661These are inherited by children of the shell, 2662and is used in a limited manner by the shell itself. 2663.It Ev PWD 2664An absolute pathname for the current directory, 2665possibly containing symbolic links. 2666This is used and updated by the shell. 2667.It Ev TERM 2668The default terminal setting for the shell. 2669This is inherited by children of the shell, and is used in the history 2670editing modes. 2671.El 2672.Pp 2673Additionally, all environment variables are turned into shell variables 2674at startup, 2675which may affect the shell as described under 2676.Sx Special Variables . 2677.Sh EXIT STATUS 2678Errors that are detected by the shell, such as a syntax error, will 2679cause the shell to exit with a non-zero exit status. 2680If the shell is not an interactive shell, the execution of the shell 2681file will be aborted. 2682Otherwise the shell will return the exit status of the last command 2683executed, or if the 2684.Ic exit 2685builtin is used with a numeric argument, it 2686will return the argument. 2687.Sh SEE ALSO 2688.Xr builtin 1 , 2689.Xr chsh 1 , 2690.Xr echo 1 , 2691.Xr ed 1 , 2692.Xr emacs 1 , 2693.Xr kill 1 , 2694.Xr printf 1 , 2695.Xr pwd 1 , 2696.Xr test 1 , 2697.Xr vi 1 , 2698.Xr execve 2 , 2699.Xr getrlimit 2 , 2700.Xr umask 2 , 2701.Xr wctype 3 , 2702.Xr editrc 5 2703.Sh HISTORY 2704A 2705.Nm 2706command, the Thompson shell, appeared in 2707.At v1 . 2708It was superseded in 2709.At v7 2710by the Bourne shell, which inherited the name 2711.Nm . 2712.Pp 2713This version of 2714.Nm 2715was rewritten in 1989 under the 2716.Bx 2717license after the Bourne shell from 2718.At V.4 . 2719.Sh AUTHORS 2720This version of 2721.Nm 2722was originally written by 2723.An Kenneth Almquist . 2724.Sh BUGS 2725The 2726.Nm 2727utility does not recognize multibyte characters other than UTF-8. 2728Splitting using 2729.Va IFS 2730and the line editing library 2731.Xr editline 3 2732do not recognize multibyte characters. 2733