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.\" 3. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 37.\" $FreeBSD: src/bin/sh/sh.1,v 1.174 2011/07/10 15:02:25 jilles Exp $ 38.\" 39.Dd August 21, 2011 40.Dt SH 1 41.Os 42.Sh NAME 43.Nm sh 44.Nd command interpreter (shell) 45.Sh SYNOPSIS 46.Nm 47.Op Fl /+abCEefIimnPpTuVvx 48.Op Fl /+o Ar longname 49.Oo 50.Ar script 51.Op Ar arg ... 52.Oc 53.Nm 54.Op Fl /+abCEefIimnPpTuVvx 55.Op Fl /+o Ar longname 56.Fl c Ar string 57.Oo 58.Ar name 59.Op Ar arg ... 60.Oc 61.Nm 62.Op Fl /+abCEefIimnPpTuVvx 63.Op Fl /+o Ar longname 64.Fl s 65.Op Ar arg ... 66.Sh DESCRIPTION 67The 68.Nm 69utility is the standard command interpreter for the system. 70The current version of 71.Nm 72is close to the 73.St -p1003.1 74specification for the shell. 75It only supports features 76designated by 77.Tn POSIX , 78plus a few Berkeley extensions. 79This man page is not intended to be a tutorial nor a complete 80specification of the shell. 81.Ss Overview 82The shell is a command that reads lines from 83either a file or the terminal, interprets them, and 84generally executes other commands. 85It is the program that is started when a user logs into the system, 86although a user can select a different shell with the 87.Xr chsh 1 88command. 89The shell 90implements a language that has flow control constructs, 91a macro facility that provides a variety of features in 92addition to data storage, along with built-in history and line 93editing capabilities. 94It incorporates many features to 95aid interactive use and has the advantage that the interpretative 96language is common to both interactive and non-interactive 97use (shell scripts). 98That is, commands can be typed directly 99to the running shell or can be put into a file, 100which can be executed directly by the shell. 101.Ss Invocation 102.\" 103.\" XXX This next sentence is incredibly confusing. 104.\" 105If no arguments are present and if the standard input of the shell 106is connected to a terminal 107(or if the 108.Fl i 109option is set), 110the shell is considered an interactive shell. 111An interactive shell 112generally prompts before each command and handles programming 113and command errors differently (as described below). 114When first starting, the shell inspects argument 0, and 115if it begins with a dash 116.Pq Ql - , 117the shell is also considered a login shell. 118This is normally done automatically by the system 119when the user first logs in. 120A login shell first reads commands 121from the files 122.Pa /etc/profile 123and then 124.Pa .profile 125in a user's home directory, 126if they exist. 127If the environment variable 128.Ev ENV 129is set on entry to a shell, or is set in the 130.Pa .profile 131of a login shell, the shell then subjects its value to parameter expansion 132and arithmetic expansion and reads commands from the named file. 133Therefore, a user should place commands that are to be executed only 134at login time in the 135.Pa .profile 136file, and commands that are executed for every shell inside the 137.Ev ENV 138file. 139The user can set the 140.Ev ENV 141variable to some file by placing the following line in the file 142.Pa .profile 143in the home directory, 144substituting for 145.Pa .shinit 146the filename desired: 147.Pp 148.Dl "ENV=$HOME/.shinit; export ENV" 149.Pp 150The first non-option argument specified on the command line 151will be treated as the 152name of a file from which to read commands (a shell script), and 153the remaining arguments are set as the positional parameters 154of the shell 155.Li ( $1 , $2 , 156etc.). 157Otherwise, the shell reads commands 158from its standard input. 159.Pp 160Unlike older versions of 161.Nm 162the 163.Ev ENV 164script is only sourced on invocation of interactive shells. 165This 166closes a well-known, and sometimes easily exploitable security 167hole related to poorly thought out 168.Ev ENV 169scripts. 170.Ss Argument List Processing 171All of the single letter options to 172.Nm 173have a corresponding long name, 174with the exception of 175.Fl c 176and 177.Fl /+o . 178These long names are provided next to the single letter options 179in the descriptions below. 180The long name for an option may be specified as an argument to the 181.Fl /+o 182option of 183.Nm . 184Once the shell is running, 185the long name for an option may be specified as an argument to the 186.Fl /+o 187option of the 188.Ic set 189built-in command 190(described later in the section called 191.Sx Built-in Commands ) . 192Introducing an option with a dash 193.Pq Ql - 194enables the option, 195while using a plus 196.Pq Ql + 197disables the option. 198A 199.Dq Li -- 200or plain 201.Ql - 202will stop option processing and will force the remaining 203words on the command line to be treated as arguments. 204The 205.Fl /+o 206and 207.Fl c 208options do not have long names. 209They take arguments and are described after the single letter options. 210.Bl -tag -width indent 211.It Fl a Li allexport 212Flag variables for export when assignments are made to them. 213.It Fl b Li notify 214Enable asynchronous notification of background job 215completion. 216(UNIMPLEMENTED) 217.It Fl C Li noclobber 218Do not overwrite existing files with 219.Ql > . 220.It Fl E Li emacs 221Enable the built-in 222.Xr emacs 1 223command line editor (disables the 224.Fl V 225option if it has been set; 226set automatically when interactive on terminals). 227.It Fl e Li errexit 228Exit immediately if any untested command fails in non-interactive mode. 229The exit status of a command is considered to be 230explicitly tested if the command is part of the list used to control 231an 232.Ic if , elif , while , 233or 234.Ic until ; 235if the command is the left 236hand operand of an 237.Dq Li && 238or 239.Dq Li || 240operator; or if the command is a pipeline preceded by the 241.Ic !\& 242operator. 243If a shell function is executed and its exit status is explicitly 244tested, all commands of the function are considered to be tested as 245well. 246.It Fl f Li noglob 247Disable pathname expansion. 248.It Fl h Li trackall 249A do-nothing option for 250.Tn POSIX 251compliance. 252.It Fl I Li ignoreeof 253Ignore 254.Dv EOF Ap s 255from input when in interactive mode. 256.It Fl i Li interactive 257Force the shell to behave interactively. 258.It Fl m Li monitor 259Turn on job control (set automatically when interactive). 260.It Fl n Li noexec 261If not interactive, read commands but do not 262execute them. 263This is useful for checking the 264syntax of shell scripts. 265.It Fl P Li physical 266Change the default for the 267.Ic cd 268and 269.Ic pwd 270commands from 271.Fl L 272(logical directory layout) 273to 274.Fl P 275(physical directory layout). 276.It Fl p Li privileged 277Turn on privileged mode. 278This mode is enabled on startup 279if either the effective user or group ID is not equal to the 280real user or group ID. 281Turning this mode off sets the 282effective user and group IDs to the real user and group IDs. 283When this mode is enabled for interactive shells, the file 284.Pa /etc/suid_profile 285is sourced instead of 286.Pa ~/.profile 287after 288.Pa /etc/profile 289is sourced, and the contents of the 290.Ev ENV 291variable are ignored. 292.It Fl s Li stdin 293Read commands from standard input (set automatically 294if no file arguments are present). 295This option has 296no effect when set after the shell has already started 297running (i.e., when set with the 298.Ic set 299command). 300.It Fl T Li trapsasync 301When waiting for a child, execute traps immediately. 302If this option is not set, 303traps are executed after the child exits, 304as specified in 305.St -p1003.2 . 306This nonstandard option is useful for putting guarding shells around 307children that block signals. 308The surrounding shell may kill the child 309or it may just return control to the tty and leave the child alone, 310like this: 311.Bd -literal -offset indent 312sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 313.Ed 314.It Fl u Li nounset 315Write a message to standard error when attempting 316to expand a variable, a positional parameter or 317the special parameter 318.Va \&! 319that is not set, and if the 320shell is not interactive, exit immediately. 321.It Fl V Li vi 322Enable the built-in 323.Xr vi 1 324command line editor (disables 325.Fl E 326if it has been set). 327.It Fl v Li verbose 328The shell writes its input to standard error 329as it is read. 330Useful for debugging. 331.It Fl x Li xtrace 332Write each command 333(preceded by the value of the 334.Va PS4 335variable subjected to parameter expansion and arithmetic expansion) 336to standard error before it is executed. 337Useful for debugging. 338.It "\ \ " Em tabcomplete 339Enables filename completion in the command line editor. 340Typing a tab character will extend the current input word to match a 341filename. 342If more than one filename matches it is only extended to be the common prefix. 343Typing a second tab character will list all the matching names. 344Turned on by default in an interactive shell. 345.El 346.Pp 347The 348.Fl c 349option causes the commands to be read from the 350.Ar string 351operand instead of from the standard input. 352Keep in mind that this option only accepts a single string as its 353argument, hence multi-word strings must be quoted. 354.Pp 355The 356.Fl /+o 357option takes as its only argument the long name of an option 358to be enabled or disabled. 359For example, the following two invocations of 360.Nm 361both enable the built-in 362.Xr emacs 1 363command line editor: 364.Bd -literal -offset indent 365set -E 366set -o emacs 367.Ed 368.Pp 369If used without an argument, the 370.Fl o 371option displays the current option settings in a human-readable format. 372If 373.Cm +o 374is used without an argument, the current option settings are output 375in a format suitable for re-input into the shell. 376.Ss Lexical Structure 377The shell reads input in terms of lines from a file and breaks 378it up into words at whitespace (blanks and tabs), and at 379certain sequences of 380characters called 381.Dq operators , 382which are special to the shell. 383There are two types of operators: control operators and 384redirection operators (their meaning is discussed later). 385The following is a list of valid operators: 386.Bl -tag -width indent 387.It Control operators: 388.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 389.It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en 390.It Li ;; Ta Li ;& Ta Li ; Ta Li | Ta Li || 391.El 392.It Redirection operators: 393.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 394.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 395.It Li <& Ta Li >& Ta Li <<- Ta Li >| 396.El 397.El 398.Pp 399The character 400.Ql # 401introduces a comment if used at the beginning of a word. 402The word starting with 403.Ql # 404and the rest of the line are ignored. 405.Pp 406.Tn ASCII 407.Dv NUL 408characters (character code 0) are not allowed in shell input. 409.Ss Quoting 410Quoting is used to remove the special meaning of certain characters 411or words to the shell, such as operators, whitespace, keywords, 412or alias names. 413.Pp 414There are four types of quoting: matched single quotes, 415dollar-single quotes, 416matched double quotes, and backslash. 417.Bl -tag -width indent 418.It Single Quotes 419Enclosing characters in single quotes preserves the literal 420meaning of all the characters (except single quotes, making 421it impossible to put single-quotes in a single-quoted string). 422.It Dollar-Single Quotes 423Enclosing characters between 424.Li $' 425and 426.Li ' 427preserves the literal meaning of all characters 428except backslashes and single quotes. 429A backslash introduces a C-style escape sequence: 430.Bl -tag -width xUnnnnnnnn 431.It \ea 432Alert (ring the terminal bell) 433.It \eb 434Backspace 435.It \ec Ns Ar c 436The control character denoted by 437.Li ^ Ns Ar c 438in 439.Xr stty 1 . 440If 441.Ar c 442is a backslash, it must be doubled. 443.It \ee 444The ESC character 445.Tn ( ASCII 4460x1b) 447.It \ef 448Formfeed 449.It \en 450Newline 451.It \er 452Carriage return 453.It \et 454Horizontal tab 455.It \ev 456Vertical tab 457.It \e\e 458Literal backslash 459.It \e\&' 460Literal single-quote 461.It \e\&" 462Literal double-quote 463.It \e Ns Ar nnn 464The byte whose octal value is 465.Ar nnn 466(one to three digits) 467.It \ex Ns Ar nn 468The byte whose hexadecimal value is 469.Ar nn 470(one or more digits only the last two of which are used) 471.It \eu Ns Ar nnnn 472The Unicode code point 473.Ar nnnn 474(four hexadecimal digits) 475.It \eU Ns Ar nnnnnnnn 476The Unicode code point 477.Ar nnnnnnnn 478(eight hexadecimal digits) 479.El 480.Pp 481The sequences for Unicode code points are currently only useful with 482UTF-8 locales. 483They reject code point 0 and UTF-16 surrogates. 484.Pp 485If an escape sequence would produce a byte with value 0, 486that byte and the rest of the string until the matching single-quote 487are ignored. 488.Pp 489Any other string starting with a backslash is an error. 490.It Double Quotes 491Enclosing characters within double quotes preserves the literal 492meaning of all characters except dollar sign 493.Pq Ql $ , 494backquote 495.Pq Ql ` , 496and backslash 497.Pq Ql \e . 498The backslash inside double quotes is historically weird. 499It remains literal unless it precedes the following characters, 500which it serves to quote: 501.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 502.It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en 503.El 504.It Backslash 505A backslash preserves the literal meaning of the following 506character, with the exception of the newline character 507.Pq Ql \en . 508A backslash preceding a newline is treated as a line continuation. 509.El 510.Ss Keywords 511Keywords or reserved words are words that have special meaning to the 512shell and are recognized at the beginning of a line and 513after a control operator. 514The following are keywords: 515.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 516.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 517.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 518.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 519.El 520.Ss Aliases 521An alias is a name and corresponding value set using the 522.Ic alias 523built-in command. 524Wherever the command word of a simple command may occur, 525and after checking for keywords if a keyword may occur, the shell 526checks the word to see if it matches an alias. 527If it does, it replaces it in the input stream with its value. 528For example, if there is an alias called 529.Dq Li lf 530with the value 531.Dq Li "ls -F" , 532then the input 533.Pp 534.Dl "lf foobar" 535.Pp 536would become 537.Pp 538.Dl "ls -F foobar" 539.Pp 540Aliases provide a convenient way for naive users to 541create shorthands for commands without having to learn how 542to create functions with arguments. 543Using aliases in scripts is discouraged 544because the command that defines them must be executed 545before the code that uses them is parsed. 546This is fragile and not portable. 547.Pp 548An alias name may be escaped in a command line, so that it is not 549replaced by its alias value, by using quoting characters within or 550adjacent to the alias name. 551This is most often done by prefixing 552an alias name with a backslash to execute a function, built-in, or 553normal program with the same name. 554See the 555.Sx Quoting 556subsection. 557.Ss Commands 558The shell interprets the words it reads according to a 559language, the specification of which is outside the scope 560of this man page (refer to the BNF in the 561.St -p1003.2 562document). 563Essentially though, a line is read and if 564the first word of the line (or after a control operator) 565is not a keyword, then the shell has recognized a 566simple command. 567Otherwise, a complex command or some 568other special construct may have been recognized. 569.Ss Simple Commands 570If a simple command has been recognized, the shell performs 571the following actions: 572.Bl -enum 573.It 574Leading words of the form 575.Dq Li name=value 576are stripped off and assigned to the environment of 577the simple command. 578Redirection operators and 579their arguments (as described below) are stripped 580off and saved for processing. 581.It 582The remaining words are expanded as described in 583the section called 584.Sx Word Expansions , 585and the first remaining word is considered the command 586name and the command is located. 587The remaining 588words are considered the arguments of the command. 589If no command name resulted, then the 590.Dq Li name=value 591variable assignments recognized in 1) affect the 592current shell. 593.It 594Redirections are performed as described in 595the next section. 596.El 597.Ss Redirections 598Redirections are used to change where a command reads its input 599or sends its output. 600In general, redirections open, close, or 601duplicate an existing reference to a file. 602The overall format 603used for redirection is: 604.Pp 605.D1 Oo Ar n Oc Ar redir-op file 606.Pp 607The 608.Ar redir-op 609is one of the redirection operators mentioned 610previously. 611The following gives some examples of how these 612operators can be used. 613Note that stdin and stdout are commonly used abbreviations 614for standard input and standard output respectively. 615.Bl -tag -width "1234567890XX" -offset indent 616.It Oo Ar n Oc Ns Li > Ar file 617redirect stdout (or file descriptor 618.Ar n ) 619to 620.Ar file 621.It Oo Ar n Oc Ns Li >| Ar file 622same as above, but override the 623.Fl C 624option 625.It Oo Ar n Oc Ns Li >> Ar file 626append stdout (or file descriptor 627.Ar n ) 628to 629.Ar file 630.It Oo Ar n Oc Ns Li < Ar file 631redirect stdin (or file descriptor 632.Ar n ) 633from 634.Ar file 635.It Oo Ar n Oc Ns Li <> Ar file 636redirect stdin (or file descriptor 637.Ar n ) 638to and from 639.Ar file 640.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 641duplicate stdin (or file descriptor 642.Ar n1 ) 643from file descriptor 644.Ar n2 645.It Oo Ar n Oc Ns Li <&- 646close stdin (or file descriptor 647.Ar n ) 648.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 649duplicate stdout (or file descriptor 650.Ar n1 ) 651to file descriptor 652.Ar n2 653.It Oo Ar n Oc Ns Li >&- 654close stdout (or file descriptor 655.Ar n ) 656.El 657.Pp 658The following redirection is often called a 659.Dq here-document . 660.Bd -unfilled -offset indent 661.Oo Ar n Oc Ns Li << Ar delimiter 662.D1 Ar here-doc-text 663.D1 ... 664.Ar delimiter 665.Ed 666.Pp 667All the text on successive lines up to the delimiter is 668saved away and made available to the command on standard 669input, or file descriptor 670.Ar n 671if it is specified. 672If the 673.Ar delimiter 674as specified on the initial line is quoted, then the 675.Ar here-doc-text 676is treated literally, otherwise the text is subjected to 677parameter expansion, command substitution, and arithmetic 678expansion (as described in the section on 679.Sx Word Expansions ) . 680If the operator is 681.Dq Li <<- 682instead of 683.Dq Li << , 684then leading tabs 685in the 686.Ar here-doc-text 687are stripped. 688.Ss Search and Execution 689There are three types of commands: shell functions, 690built-in commands, and normal programs. 691The command is searched for (by name) in that order. 692The three types of commands are all executed in a different way. 693.Pp 694When a shell function is executed, all of the shell positional 695parameters (except 696.Li $0 , 697which remains unchanged) are 698set to the arguments of the shell function. 699The variables which are explicitly placed in the environment of 700the command (by placing assignments to them before the 701function name) are made local to the function and are set 702to the values given. 703Then the command given in the function definition is executed. 704The positional parameters are restored to their original values 705when the command completes. 706This all occurs within the current shell. 707.Pp 708Shell built-in commands are executed internally to the shell, without 709spawning a new process. 710There are two kinds of built-in commands: regular and special. 711Assignments before special builtins persist after they finish 712executing and assignment errors, redirection errors and certain 713operand errors cause a script to be aborted. 714Special builtins cannot be overridden with a function. 715Both regular and special builtins can affect the shell in ways 716normal programs cannot. 717.Pp 718Otherwise, if the command name does not match a function 719or built-in command, the command is searched for as a normal 720program in the file system (as described in the next section). 721When a normal program is executed, the shell runs the program, 722passing the arguments and the environment to the program. 723If the program is not a normal executable file 724(i.e., if it does not begin with the 725.Dq "magic number" 726whose 727.Tn ASCII 728representation is 729.Dq Li #! , 730resulting in an 731.Er ENOEXEC 732return value from 733.Xr execve 2 ) 734but appears to be a text file, 735the shell will run a new instance of 736.Nm 737to interpret it. 738.Pp 739Note that previous versions of this document 740and the source code itself misleadingly and sporadically 741refer to a shell script without a magic number 742as a 743.Dq "shell procedure" . 744.Ss Path Search 745When locating a command, the shell first looks to see if 746it has a shell function by that name. 747Then it looks for a 748built-in command by that name. 749If a built-in command is not found, 750one of two things happen: 751.Bl -enum 752.It 753Command names containing a slash are simply executed without 754performing any searches. 755.It 756The shell searches each entry in the 757.Va PATH 758variable 759in turn for the command. 760The value of the 761.Va PATH 762variable should be a series of 763entries separated by colons. 764Each entry consists of a 765directory name. 766The current directory 767may be indicated implicitly by an empty directory name, 768or explicitly by a single period. 769.El 770.Ss Command Exit Status 771Each command has an exit status that can influence the behavior 772of other shell commands. 773The paradigm is that a command exits 774with zero for normal or success, and non-zero for failure, 775error, or a false indication. 776The man page for each command 777should indicate the various exit codes and what they mean. 778Additionally, the built-in commands return exit codes, as does 779an executed shell function. 780.Pp 781If a command is terminated by a signal, its exit status is 128 plus 782the signal number. 783Signal numbers are defined in the header file 784.In sys/signal.h . 785.Ss Complex Commands 786Complex commands are combinations of simple commands 787with control operators or keywords, together creating a larger complex 788command. 789More generally, a command is one of the following: 790.Bl -item -offset indent 791.It 792simple command 793.It 794pipeline 795.It 796list or compound-list 797.It 798compound command 799.It 800function definition 801.El 802.Pp 803Unless otherwise stated, the exit status of a command is 804that of the last simple command executed by the command. 805.Ss Pipelines 806A pipeline is a sequence of one or more commands separated 807by the control operator 808.Ql \&| . 809The standard output of all but 810the last command is connected to the standard input 811of the next command. 812The standard output of the last 813command is inherited from the shell, as usual. 814.Pp 815The format for a pipeline is: 816.Pp 817.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... 818.Pp 819The standard output of 820.Ar command1 821is connected to the standard input of 822.Ar command2 . 823The standard input, standard output, or 824both of a command is considered to be assigned by the 825pipeline before any redirection specified by redirection 826operators that are part of the command. 827.Pp 828Note that unlike some other shells, 829.Nm 830executes each process in a pipeline with more than one command 831in a subshell environment and as a child of the 832.Nm 833process. 834.Pp 835If the pipeline is not in the background (discussed later), 836the shell waits for all commands to complete. 837.Pp 838If the keyword 839.Ic !\& 840does not precede the pipeline, the 841exit status is the exit status of the last command specified 842in the pipeline. 843Otherwise, the exit status is the logical 844NOT of the exit status of the last command. 845That is, if 846the last command returns zero, the exit status is 1; if 847the last command returns greater than zero, the exit status 848is zero. 849.Pp 850Because pipeline assignment of standard input or standard 851output or both takes place before redirection, it can be 852modified by redirection. 853For example: 854.Pp 855.Dl "command1 2>&1 | command2" 856.Pp 857sends both the standard output and standard error of 858.Ar command1 859to the standard input of 860.Ar command2 . 861.Pp 862A 863.Ql \&; 864or newline terminator causes the preceding 865AND-OR-list 866(described below in the section called 867.Sx Short-Circuit List Operators ) 868to be executed sequentially; 869an 870.Ql & 871causes asynchronous execution of the preceding AND-OR-list. 872.Ss Background Commands (&) 873If a command is terminated by the control operator ampersand 874.Pq Ql & , 875the shell executes the command in a subshell environment (see 876.Sx Grouping Commands Together 877below) and asynchronously; 878the shell does not wait for the command to finish 879before executing the next command. 880.Pp 881The format for running a command in background is: 882.Pp 883.D1 Ar command1 Li & Op Ar command2 Li & Ar ... 884.Pp 885If the shell is not interactive, the standard input of an 886asynchronous command is set to 887.Pa /dev/null . 888.Ss Lists (Generally Speaking) 889A list is a sequence of zero or more commands separated by 890newlines, semicolons, or ampersands, 891and optionally terminated by one of these three characters. 892The commands in a 893list are executed in the order they are written. 894If command is followed by an ampersand, the shell starts the 895command and immediately proceeds onto the next command; 896otherwise it waits for the command to terminate before 897proceeding to the next one. 898.Ss Short-Circuit List Operators 899.Dq Li && 900and 901.Dq Li || 902are AND-OR list operators. 903.Dq Li && 904executes the first command, and then executes the second command 905if the exit status of the first command is zero. 906.Dq Li || 907is similar, but executes the second command if the exit 908status of the first command is nonzero. 909.Dq Li && 910and 911.Dq Li || 912both have the same priority. 913.Ss Flow-Control Constructs (if, while, for, case) 914The syntax of the 915.Ic if 916command is: 917.Bd -unfilled -offset indent -compact 918.Ic if Ar list 919.Ic then Ar list 920.Oo Ic elif Ar list 921.Ic then Ar list Oc Ar ... 922.Op Ic else Ar list 923.Ic fi 924.Ed 925.Pp 926The syntax of the 927.Ic while 928command is: 929.Bd -unfilled -offset indent -compact 930.Ic while Ar list 931.Ic do Ar list 932.Ic done 933.Ed 934.Pp 935The two lists are executed repeatedly while the exit status of the 936first list is zero. 937The 938.Ic until 939command is similar, but has the word 940.Ic until 941in place of 942.Ic while , 943which causes it to 944repeat until the exit status of the first list is zero. 945.Pp 946The syntax of the 947.Ic for 948command is: 949.Bd -unfilled -offset indent -compact 950.Ic for Ar variable Op Ic in Ar word ... 951.Ic do Ar list 952.Ic done 953.Ed 954.Pp 955If 956.Ic in 957and the following words are omitted, 958.Ic in Li \&"$@\&" 959is used instead. 960The words are expanded, and then the list is executed 961repeatedly with the variable set to each word in turn. 962The 963.Ic do 964and 965.Ic done 966commands may be replaced with 967.Ql { 968and 969.Ql } . 970.Pp 971The syntax of the 972.Ic break 973and 974.Ic continue 975commands is: 976.D1 Ic break Op Ar num 977.D1 Ic continue Op Ar num 978.Pp 979The 980.Ic break 981command terminates the 982.Ar num 983innermost 984.Ic for 985or 986.Ic while 987loops. 988The 989.Ic continue 990command continues with the next iteration of the innermost loop. 991These are implemented as special built-in commands. 992.Pp 993The syntax of the 994.Ic case 995command is: 996.Bd -unfilled -offset indent -compact 997.Ic case Ar word Ic in 998.Ar pattern Ns Li ) Ar list Li ;; 999.Ar ... 1000.Ic esac 1001.Ed 1002.Pp 1003The pattern can actually be one or more patterns 1004(see 1005.Sx Shell Patterns 1006described later), 1007separated by 1008.Ql \&| 1009characters. 1010Tilde expansion, parameter expansion, command substitution, 1011arithmetic expansion and quote removal are applied to the word. 1012Then, each pattern is expanded in turn using tilde expansion, 1013parameter expansion, command substitution and arithmetic expansion and 1014the expanded form of the word is checked against it. 1015If a match is found, the corresponding list is executed. 1016If the selected list is terminated by the control operator 1017.Ql ;& 1018instead of 1019.Ql ;; , 1020execution continues with the next list, 1021continuing until a list terminated with 1022.Ql ;; 1023or the end of the 1024.Ic case 1025command. 1026The exit code of the 1027.Ic case 1028command is the exit code of the last command executed in the list or 1029zero if no patterns were matched. 1030.Ss Grouping Commands Together 1031Commands may be grouped by writing either 1032.Pp 1033.D1 Li \&( Ns Ar list Ns Li \%) 1034.Pp 1035or 1036.Pp 1037.D1 Li { Ar list Ns Li \&; } 1038.Pp 1039The first form executes the commands in a subshell environment. 1040A subshell environment has its own copy of: 1041.Bl -enum 1042.It 1043The current working directory as set by 1044.Ic cd . 1045.It 1046The file creation mask as set by 1047.Ic umask . 1048.It 1049References to open files. 1050.It 1051Traps as set by 1052.Ic trap . 1053.It 1054Known jobs. 1055.It 1056Positional parameters and variables. 1057.It 1058Shell options. 1059.It 1060Shell functions. 1061.It 1062Shell aliases. 1063.El 1064.Pp 1065These are copied from the parent shell environment, 1066except that trapped (but not ignored) signals are reset to the default action 1067and known jobs are cleared. 1068Any changes do not affect the parent shell environment. 1069.Pp 1070A subshell environment may be implemented as a child process or differently. 1071If job control is enabled in an interactive shell, 1072commands grouped in parentheses can be suspended and continued as a unit. 1073.Pp 1074The second form never forks another shell, 1075so it is slightly more efficient. 1076Grouping commands together this way allows the user to 1077redirect their output as though they were one program: 1078.Bd -literal -offset indent 1079{ echo -n "hello"; echo " world"; } > greeting 1080.Ed 1081.Ss Functions 1082The syntax of a function definition is 1083.Pp 1084.D1 Ar name Li \&( \&) Ar command 1085.Pp 1086A function definition is an executable statement; when 1087executed it installs a function named 1088.Ar name 1089and returns an 1090exit status of zero. 1091The 1092.Ar command 1093is normally a list 1094enclosed between 1095.Ql { 1096and 1097.Ql } . 1098.Pp 1099Variables may be declared to be local to a function by 1100using the 1101.Ic local 1102command. 1103This should appear as the first statement of a function, 1104and the syntax is: 1105.Pp 1106.D1 Ic local Oo Ar variable ... Oc Op Fl 1107.Pp 1108The 1109.Ic local 1110command is implemented as a built-in command. 1111.Pp 1112When a variable is made local, it inherits the initial 1113value and exported and readonly flags from the variable 1114with the same name in the surrounding scope, if there is 1115one. 1116Otherwise, the variable is initially unset. 1117The shell 1118uses dynamic scoping, so that if the variable 1119.Va x 1120is made local to function 1121.Em f , 1122which then calls function 1123.Em g , 1124references to the variable 1125.Va x 1126made inside 1127.Em g 1128will refer to the variable 1129.Va x 1130declared inside 1131.Em f , 1132not to the global variable named 1133.Va x . 1134.Pp 1135The only special parameter that can be made local is 1136.Ql - . 1137Making 1138.Ql - 1139local causes any shell options that are 1140changed via the 1141.Ic set 1142command inside the function to be 1143restored to their original values when the function 1144returns. 1145.Pp 1146The syntax of the 1147.Ic return 1148command is 1149.Pp 1150.D1 Ic return Op Ar exitstatus 1151.Pp 1152It terminates the current executional scope, returning from the previous 1153nested function, sourced script, or shell instance, in that order. 1154The 1155.Ic return 1156command is implemented as a special built-in command. 1157.Ss Variables and Parameters 1158The shell maintains a set of parameters. 1159A parameter 1160denoted by a name is called a variable. 1161When starting up, 1162the shell turns all the environment variables into shell 1163variables. 1164New variables can be set using the form 1165.Pp 1166.D1 Ar name Ns = Ns Ar value 1167.Pp 1168Variables set by the user must have a name consisting solely 1169of alphabetics, numerics, and underscores. 1170The first letter of a variable name must not be numeric. 1171A parameter can also be denoted by a number 1172or a special character as explained below. 1173.Ss Positional Parameters 1174A positional parameter is a parameter denoted by a number greater than zero. 1175The shell sets these initially to the values of its command line 1176arguments that follow the name of the shell script. 1177The 1178.Ic set 1179built-in command can also be used to set or reset them. 1180.Ss Special Parameters 1181Special parameters are parameters denoted by a single special character 1182or the digit zero. 1183They are shown in the following list, exactly as they would appear in input 1184typed by the user or in the source of a shell script. 1185.Bl -hang 1186.It Li $* 1187Expands to the positional parameters, starting from one. 1188When 1189the expansion occurs within a double-quoted string 1190it expands to a single field with the value of each parameter 1191separated by the first character of the 1192.Va IFS 1193variable, 1194or by a space if 1195.Va IFS 1196is unset. 1197.It Li $@ 1198Expands to the positional parameters, starting from one. 1199When 1200the expansion occurs within double-quotes, each positional 1201parameter expands as a separate argument. 1202If there are no positional parameters, the 1203expansion of 1204.Li @ 1205generates zero arguments, even when 1206.Li @ 1207is double-quoted. 1208What this basically means, for example, is 1209if 1210.Li $1 1211is 1212.Dq Li abc 1213and 1214.Li $2 1215is 1216.Dq Li "def ghi" , 1217then 1218.Li \&"$@\&" 1219expands to 1220the two arguments: 1221.Bd -literal -offset indent 1222"abc" "def ghi" 1223.Ed 1224.It Li $# 1225Expands to the number of positional parameters. 1226.It Li $? 1227Expands to the exit status of the most recent pipeline. 1228.It Li $- 1229(hyphen) Expands to the current option flags (the single-letter 1230option names concatenated into a string) as specified on 1231invocation, by the 1232.Ic set 1233built-in command, or implicitly 1234by the shell. 1235.It Li $$ 1236Expands to the process ID of the invoked shell. 1237A subshell 1238retains the same value of 1239.Va $ 1240as its parent. 1241.It Li $! 1242Expands to the process ID of the most recent background 1243command executed from the current shell. 1244For a 1245pipeline, the process ID is that of the last command in the 1246pipeline. 1247If this parameter is referenced, the shell will remember 1248the process ID and its exit status until the 1249.Ic wait 1250built-in command reports completion of the process. 1251.It Li $0 1252(zero) Expands to the name of the shell script if passed on the command line, 1253the 1254.Ar name 1255operand if given (with 1256.Fl c ) 1257or otherwise argument 0 passed to the shell. 1258.El 1259.Ss Special Variables 1260The following variables are set by the shell or 1261have special meaning to it: 1262.Bl -tag -width ".Va HISTSIZE" 1263.It Va CDPATH 1264The search path used with the 1265.Ic cd 1266built-in. 1267.It Va EDITOR 1268The fallback editor used with the 1269.Ic fc 1270built-in. 1271If not set, the default editor is 1272.Xr ed 1 . 1273.It Va FCEDIT 1274The default editor used with the 1275.Ic fc 1276built-in. 1277.It Va HISTSIZE 1278The number of previous commands that are accessible. 1279.It Va HOME 1280The user's home directory, 1281used in tilde expansion and as a default directory for the 1282.Ic cd 1283built-in. 1284.It Va IFS 1285Input Field Separators. 1286This is normally set to 1287.Aq space , 1288.Aq tab , 1289and 1290.Aq newline . 1291See the 1292.Sx White Space Splitting 1293section for more details. 1294.It Va LINENO 1295The current line number in the script or function. 1296.It Va MAIL 1297The name of a mail file, that will be checked for the arrival of new 1298mail. 1299Overridden by 1300.Va MAILPATH . 1301.It Va MAILPATH 1302A colon 1303.Pq Ql \&: 1304separated list of file names, for the shell to check for incoming 1305mail. 1306This variable overrides the 1307.Va MAIL 1308setting. 1309There is a maximum of 10 mailboxes that can be monitored at once. 1310.It Va PATH 1311The default search path for executables. 1312See the 1313.Sx Path Search 1314section for details. 1315.It Va PPID 1316The parent process ID of the invoked shell. 1317This is set at startup 1318unless this variable is in the environment. 1319A later change of parent process ID is not reflected. 1320A subshell retains the same value of 1321.Va PPID . 1322.It Va PS1 1323The primary prompt string, which defaults to 1324.Dq Li "$ " , 1325unless you are the superuser, in which case it defaults to 1326.Dq Li "# " . 1327.It Va PS2 1328The secondary prompt string, which defaults to 1329.Dq Li "> " . 1330.It Va PS4 1331The prefix for the trace output (if 1332.Fl x 1333is active). 1334The default is 1335.Dq Li "+ " . 1336.El 1337.Ss Word Expansions 1338This clause describes the various expansions that are 1339performed on words. 1340Not all expansions are performed on 1341every word, as explained later. 1342.Pp 1343Tilde expansions, parameter expansions, command substitutions, 1344arithmetic expansions, and quote removals that occur within 1345a single word expand to a single field. 1346It is only field 1347splitting or pathname expansion that can create multiple 1348fields from a single word. 1349The single exception to this rule is 1350the expansion of the special parameter 1351.Va @ 1352within double-quotes, 1353as was described above. 1354.Pp 1355The order of word expansion is: 1356.Bl -enum 1357.It 1358Tilde Expansion, Parameter Expansion, Command Substitution, 1359Arithmetic Expansion (these all occur at the same time). 1360.It 1361Field Splitting is performed on fields generated by step (1) 1362unless the 1363.Va IFS 1364variable is null. 1365.It 1366Pathname Expansion (unless the 1367.Fl f 1368option is in effect). 1369.It 1370Quote Removal. 1371.El 1372.Pp 1373The 1374.Ql $ 1375character is used to introduce parameter expansion, command 1376substitution, or arithmetic expansion. 1377.Ss Tilde Expansion (substituting a user's home directory) 1378A word beginning with an unquoted tilde character 1379.Pq Ql ~ 1380is 1381subjected to tilde expansion. 1382All the characters up to a slash 1383.Pq Ql / 1384or the end of the word are treated as a username 1385and are replaced with the user's home directory. 1386If the 1387username is missing (as in 1388.Pa ~/foobar ) , 1389the tilde is replaced with the value of the 1390.Va HOME 1391variable (the current user's home directory). 1392.Ss Parameter Expansion 1393The format for parameter expansion is as follows: 1394.Pp 1395.D1 Li ${ Ns Ar expression Ns Li } 1396.Pp 1397where 1398.Ar expression 1399consists of all characters until the matching 1400.Ql } . 1401Any 1402.Ql } 1403escaped by a backslash or within a single-quoted or double-quoted 1404string, and characters in 1405embedded arithmetic expansions, command substitutions, and variable 1406expansions, are not examined in determining the matching 1407.Ql } . 1408If the variants with 1409.Ql + , 1410.Ql - , 1411.Ql = 1412or 1413.Ql ?\& 1414occur within a double-quoted string, 1415as an extension there may be unquoted parts 1416(via double-quotes inside the expansion); 1417.Ql } 1418within such parts are also not examined in determining the matching 1419.Ql } . 1420.Pp 1421The simplest form for parameter expansion is: 1422.Pp 1423.D1 Li ${ Ns Ar parameter Ns Li } 1424.Pp 1425The value, if any, of 1426.Ar parameter 1427is substituted. 1428.Pp 1429The parameter name or symbol can be enclosed in braces, which are 1430optional except for positional parameters with more than one digit or 1431when parameter is followed by a character that could be interpreted as 1432part of the name. 1433If a parameter expansion occurs inside double-quotes: 1434.Bl -enum 1435.It 1436Pathname expansion is not performed on the results of the 1437expansion. 1438.It 1439Field splitting is not performed on the results of the 1440expansion, with the exception of the special parameter 1441.Va @ . 1442.El 1443.Pp 1444In addition, a parameter expansion can be modified by using one of the 1445following formats. 1446.Bl -tag -width indent 1447.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1448Use Default Values. 1449If 1450.Ar parameter 1451is unset or null, the expansion of 1452.Ar word 1453is substituted; otherwise, the value of 1454.Ar parameter 1455is substituted. 1456.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1457Assign Default Values. 1458If 1459.Ar parameter 1460is unset or null, the expansion of 1461.Ar word 1462is assigned to 1463.Ar parameter . 1464In all cases, the 1465final value of 1466.Ar parameter 1467is substituted. 1468Quoting inside 1469.Ar word 1470does not prevent field splitting or pathname expansion. 1471Only variables, not positional 1472parameters or special parameters, can be 1473assigned in this way. 1474.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1475Indicate Error if Null or Unset. 1476If 1477.Ar parameter 1478is unset or null, the expansion of 1479.Ar word 1480(or a message indicating it is unset if 1481.Ar word 1482is omitted) is written to standard 1483error and the shell exits with a nonzero 1484exit status. 1485Otherwise, the value of 1486.Ar parameter 1487is substituted. 1488An 1489interactive shell need not exit. 1490.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1491Use Alternate Value. 1492If 1493.Ar parameter 1494is unset or null, null is substituted; 1495otherwise, the expansion of 1496.Ar word 1497is substituted. 1498.El 1499.Pp 1500In the parameter expansions shown previously, use of the colon in the 1501format results in a test for a parameter that is unset or null; omission 1502of the colon results in a test for a parameter that is only unset. 1503.Pp 1504The 1505.Ar word 1506inherits the type of quoting 1507(unquoted, double-quoted or here-document) 1508from the surroundings, 1509with the exception that a backslash that quotes a closing brace is removed 1510during quote removal. 1511.Bl -tag -width indent 1512.It Li ${# Ns Ar parameter Ns Li } 1513String Length. 1514The length in characters of 1515the value of 1516.Ar parameter . 1517.El 1518.Pp 1519The following four varieties of parameter expansion provide for substring 1520processing. 1521In each case, pattern matching notation 1522(see 1523.Sx Shell Patterns ) , 1524rather than regular expression notation, 1525is used to evaluate the patterns. 1526If parameter is one of the special parameters 1527.Va * 1528or 1529.Va @ , 1530the result of the expansion is unspecified. 1531Enclosing the full parameter expansion string in double-quotes does not 1532cause the following four varieties of pattern characters to be quoted, 1533whereas quoting characters within the braces has this effect. 1534.Bl -tag -width indent 1535.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1536Remove Smallest Suffix Pattern. 1537The 1538.Ar word 1539is expanded to produce a pattern. 1540The 1541parameter expansion then results in 1542.Ar parameter , 1543with the smallest portion of the 1544suffix matched by the pattern deleted. 1545.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1546Remove Largest Suffix Pattern. 1547The 1548.Ar word 1549is expanded to produce a pattern. 1550The 1551parameter expansion then results in 1552.Ar parameter , 1553with the largest portion of the 1554suffix matched by the pattern deleted. 1555.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1556Remove Smallest Prefix Pattern. 1557The 1558.Ar word 1559is expanded to produce a pattern. 1560The 1561parameter expansion then results in 1562.Ar parameter , 1563with the smallest portion of the 1564prefix matched by the pattern deleted. 1565.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1566Remove Largest Prefix Pattern. 1567The 1568.Ar word 1569is expanded to produce a pattern. 1570The 1571parameter expansion then results in 1572.Ar parameter , 1573with the largest portion of the 1574prefix matched by the pattern deleted. 1575.El 1576.Ss Command Substitution 1577Command substitution allows the output of a command to be substituted in 1578place of the command name itself. 1579Command substitution occurs when 1580the command is enclosed as follows: 1581.Pp 1582.D1 Li $( Ns Ar command Ns Li )\& 1583.Pp 1584or the backquoted version: 1585.Pp 1586.D1 Li ` Ns Ar command Ns Li ` 1587.Pp 1588The shell expands the command substitution by executing command 1589and replacing the command substitution 1590with the standard output of the command, 1591removing sequences of one or more newlines at the end of the substitution. 1592Embedded newlines before the end of the output are not removed; 1593however, during field splitting, they may be translated into spaces 1594depending on the value of 1595.Va IFS 1596and the quoting that is in effect. 1597The command is executed in a subshell environment, 1598except that the built-in commands 1599.Ic jobid , 1600.Ic jobs , 1601and 1602.Ic trap 1603return information about the parent shell environment 1604and 1605.Ic times 1606returns information about the same process 1607if they are the only command in a command substitution. 1608.Ss Arithmetic Expansion 1609Arithmetic expansion provides a mechanism for evaluating an arithmetic 1610expression and substituting its value. 1611The format for arithmetic expansion is as follows: 1612.Pp 1613.D1 Li $(( Ns Ar expression Ns Li )) 1614.Pp 1615The 1616.Ar expression 1617is treated as if it were in double-quotes, except 1618that a double-quote inside the expression is not treated specially. 1619The 1620shell expands all tokens in the 1621.Ar expression 1622for parameter expansion, 1623command substitution, 1624arithmetic expansion 1625and quote removal. 1626.Pp 1627The allowed expressions are a subset of C expressions, 1628summarized below. 1629.Bl -tag -width "Variables" -offset indent 1630.It Values 1631All values are of type 1632.Ft intmax_t . 1633.It Constants 1634Decimal, octal (starting with 1635.Li 0 ) 1636and hexadecimal (starting with 1637.Li 0x ) 1638integer constants. 1639.It Variables 1640Shell variables can be read and written 1641and contain integer constants. 1642.It Unary operators 1643.Li "! ~ + -" 1644.It Binary operators 1645.Li "* / % + - << >> < <= > >= == != & ^ | && ||" 1646.It Assignment operators 1647.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1648.It Conditional operator 1649.Li "? :" 1650.El 1651.Pp 1652The result of the expression is substituted in decimal. 1653.Ss White Space Splitting (Field Splitting) 1654After parameter expansion, command substitution, and 1655arithmetic expansion the shell scans the results of 1656expansions and substitutions that did not occur in double-quotes for 1657field splitting and multiple fields can result. 1658.Pp 1659The shell treats each character of the 1660.Va IFS 1661variable as a delimiter and uses 1662the delimiters to split the results of parameter expansion and command 1663substitution into fields. 1664.Ss Pathname Expansion (File Name Generation) 1665Unless the 1666.Fl f 1667option is set, 1668file name generation is performed 1669after word splitting is complete. 1670Each word is 1671viewed as a series of patterns, separated by slashes. 1672The 1673process of expansion replaces the word with the names of 1674all existing files whose names can be formed by replacing 1675each pattern with a string that matches the specified pattern. 1676There are two restrictions on this: first, a pattern cannot match 1677a string containing a slash, and second, 1678a pattern cannot match a string starting with a period 1679unless the first character of the pattern is a period. 1680The next section describes the patterns used for 1681Pathname Expansion, 1682the four varieties of parameter expansion for substring processing and the 1683.Ic case 1684command. 1685.Ss Shell Patterns 1686A pattern consists of normal characters, which match themselves, 1687and meta-characters. 1688The meta-characters are 1689.Ql * , 1690.Ql \&? , 1691and 1692.Ql \&[ . 1693These characters lose their special meanings if they are quoted. 1694When command or variable substitution is performed and the dollar sign 1695or back quotes are not double-quoted, the value of the 1696variable or the output of the command is scanned for these 1697characters and they are turned into meta-characters. 1698.Pp 1699An asterisk 1700.Pq Ql * 1701matches any string of characters. 1702A question mark 1703.Pq Ql \&? 1704matches any single character. 1705A left bracket 1706.Pq Ql \&[ 1707introduces a character class. 1708The end of the character class is indicated by a 1709.Ql \&] ; 1710if the 1711.Ql \&] 1712is missing then the 1713.Ql \&[ 1714matches a 1715.Ql \&[ 1716rather than introducing a character class. 1717A character class matches any of the characters between the square brackets. 1718A locale-dependent range of characters may be specified using a minus sign. 1719A named class of characters (see 1720.Xr wctype 3 ) 1721may be specified by surrounding the name with 1722.Ql \&[: 1723and 1724.Ql :\&] . 1725For example, 1726.Ql \&[\&[:alpha:\&]\&] 1727is a shell pattern that matches a single letter. 1728The character class may be complemented by making an exclamation point 1729.Pq Ql !\& 1730the first character of the character class. 1731A caret 1732.Pq Ql ^ 1733has the same effect but is non-standard. 1734.Pp 1735To include a 1736.Ql \&] 1737in a character class, make it the first character listed 1738(after the 1739.Ql \&! 1740or 1741.Ql ^ , 1742if any). 1743To include a 1744.Ql - , 1745make it the first or last character listed. 1746.Ss Built-in Commands 1747This section lists the built-in commands. 1748.Bl -tag -width indent 1749.It Ic \&: 1750A null command that returns a 0 (true) exit value. 1751.It Ic \&. Ar file 1752The commands in the specified file are read and executed by the shell. 1753The 1754.Ic return 1755command may be used to return to the 1756.Ic \&. 1757command's caller. 1758If 1759.Ar file 1760contains any 1761.Ql / 1762characters, it is used as is. 1763Otherwise, the shell searches the 1764.Va PATH 1765for the file. 1766If it is not found in the 1767.Va PATH , 1768it is sought in the current working directory. 1769.It Ic \&[ 1770A built-in equivalent of 1771.Xr test 1 . 1772.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc 1773If 1774.Ar name Ns = Ns Ar string 1775is specified, the shell defines the alias 1776.Ar name 1777with value 1778.Ar string . 1779If just 1780.Ar name 1781is specified, the value of the alias 1782.Ar name 1783is printed. 1784With no arguments, the 1785.Ic alias 1786built-in command prints the names and values of all defined aliases 1787(see 1788.Ic unalias ) . 1789Alias values are written with appropriate quoting so that they are 1790suitable for re-input to the shell. 1791Also see the 1792.Sx Aliases 1793subsection. 1794.It Ic bg Op Ar job ... 1795Continue the specified jobs 1796(or the current job if no jobs are given) 1797in the background. 1798.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1799List or alter key bindings for the line editor. 1800This command is documented in 1801.Xr editrc 5 . 1802.It Ic break Op Ar num 1803See the 1804.Sx Flow-Control Constructs 1805subsection. 1806.It Ic builtin Ar cmd Op Ar arg ... 1807Execute the specified built-in command, 1808.Ar cmd . 1809This is useful when the user wishes to override a shell function 1810with the same name as a built-in command. 1811.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 1812Switch to the specified 1813.Ar directory , 1814or to the directory specified in the 1815.Va HOME 1816environment variable if no 1817.Ar directory 1818is specified. 1819If 1820.Ar directory 1821does not begin with 1822.Pa / , \&. , 1823or 1824.Pa .. , 1825then the directories listed in the 1826.Va CDPATH 1827variable will be 1828searched for the specified 1829.Ar directory . 1830If 1831.Va CDPATH 1832is unset, the current directory is searched. 1833The format of 1834.Va CDPATH 1835is the same as that of 1836.Va PATH . 1837In an interactive shell, 1838the 1839.Ic cd 1840command will print out the name of the directory 1841that it actually switched to 1842if this is different from the name that the user gave. 1843These may be different either because the 1844.Va CDPATH 1845mechanism was used or because a symbolic link was crossed. 1846.Pp 1847If the 1848.Fl P 1849option is specified, 1850.Pa .. 1851is handled physically and symbolic links are resolved before 1852.Pa .. 1853components are processed. 1854If the 1855.Fl L 1856option is specified, 1857.Pa .. 1858is handled logically. 1859This is the default. 1860.Pp 1861The 1862.Fl e 1863option causes 1864.Ic cd 1865to return exit status 1 if the full pathname of the new directory 1866cannot be determined reliably or at all. 1867Normally this is not considered an error, 1868although a warning is printed. 1869.It Ic chdir 1870A synonym for the 1871.Ic cd 1872built-in command. 1873.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 1874.It Ic command Oo Fl p Oc Fl v Ar utility 1875.It Ic command Oo Fl p Oc Fl V Ar utility 1876The first form of invocation executes the specified 1877.Ar utility , 1878ignoring shell functions in the search. 1879If 1880.Ar utility 1881is a special builtin, 1882it is executed as if it were a regular builtin. 1883.Pp 1884If the 1885.Fl p 1886option is specified, the command search is performed using a 1887default value of 1888.Va PATH 1889that is guaranteed to find all of the standard utilities. 1890.Pp 1891If the 1892.Fl v 1893option is specified, 1894.Ar utility 1895is not executed but a description of its interpretation by the shell is 1896printed. 1897For ordinary commands the output is the path name; for shell built-in 1898commands, shell functions and keywords only the name is written. 1899Aliases are printed as 1900.Dq Ic alias Ar name Ns = Ns Ar value . 1901.Pp 1902The 1903.Fl V 1904option is identical to 1905.Fl v 1906except for the output. 1907It prints 1908.Dq Ar utility Ic is Ar description 1909where 1910.Ar description 1911is either 1912the path name to 1913.Ar utility , 1914a special shell builtin, 1915a shell builtin, 1916a shell function, 1917a shell keyword 1918or 1919an alias for 1920.Ar value . 1921.It Ic continue Op Ar num 1922See the 1923.Sx Flow-Control Constructs 1924subsection. 1925.It Ic echo Oo Fl e | n Oc Op Ar string ... 1926Print a space-separated list of the arguments to the standard output 1927and append a newline character. 1928.Bl -tag -width indent 1929.It Fl n 1930Suppress the output of the trailing newline. 1931.It Fl e 1932Process C-style backslash escape sequences. 1933The 1934.Ic echo 1935command understands the following character escapes: 1936.Bl -tag -width indent 1937.It \ea 1938Alert (ring the terminal bell) 1939.It \eb 1940Backspace 1941.It \ec 1942Suppress the trailing newline (this has the side-effect of truncating the 1943line if it is not the last character) 1944.It \ee 1945The ESC character 1946.Tn ( ASCII 19470x1b) 1948.It \ef 1949Formfeed 1950.It \en 1951Newline 1952.It \er 1953Carriage return 1954.It \et 1955Horizontal tab 1956.It \ev 1957Vertical tab 1958.It \e\e 1959Literal backslash 1960.It \e0nnn 1961(Zero) The character whose octal value is 1962.Ar nnn 1963.El 1964.Pp 1965If 1966.Ar string 1967is not enclosed in quotes then the backslash itself must be escaped 1968with a backslash to protect it from the shell. 1969For example 1970.Bd -literal -offset indent 1971$ echo -e "a\evb" 1972a 1973 b 1974$ echo -e a\e\evb 1975a 1976 b 1977$ echo -e "a\e\eb" 1978a\eb 1979$ echo -e a\e\e\e\eb 1980a\eb 1981.Ed 1982.El 1983.Pp 1984Only one of the 1985.Fl e 1986and 1987.Fl n 1988options may be specified. 1989.It Ic eval Ar string ... 1990Concatenate all the arguments with spaces. 1991Then re-parse and execute the command. 1992.It Ic exec Op Ar command Op Ar arg ... 1993Unless 1994.Ar command 1995is omitted, 1996the shell process is replaced with the specified program 1997(which must be a real program, not a shell built-in command or function). 1998Any redirections on the 1999.Ic exec 2000command are marked as permanent, 2001so that they are not undone when the 2002.Ic exec 2003command finishes. 2004.It Ic exit Op Ar exitstatus 2005Terminate the shell process. 2006If 2007.Ar exitstatus 2008is given 2009it is used as the exit status of the shell. 2010Otherwise, if the shell is executing an 2011.Cm EXIT 2012trap, the exit status of the last command before the trap is used; 2013if the shell is executing a trap for a signal, 2014the shell exits by resending the signal to itself. 2015Otherwise, the exit status of the preceding command is used. 2016The exit status should be an integer between 0 and 255. 2017.It Ic export Ar name ... 2018.It Ic export Op Fl p 2019The specified names are exported so that they will 2020appear in the environment of subsequent commands. 2021The only way to un-export a variable is to 2022.Ic unset 2023it. 2024The shell allows the value of a variable to be set 2025at the same time as it is exported by writing 2026.Pp 2027.D1 Ic export Ar name Ns = Ns Ar value 2028.Pp 2029With no arguments the 2030.Ic export 2031command lists the names 2032of all exported variables. 2033If the 2034.Fl p 2035option is specified, the exported variables are printed as 2036.Dq Ic export Ar name Ns = Ns Ar value 2037lines, suitable for re-input to the shell. 2038.It Ic false 2039A null command that returns a non-zero (false) exit value. 2040.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2041.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2042.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2043The 2044.Ic fc 2045built-in command lists, or edits and re-executes, 2046commands previously entered to an interactive shell. 2047.Bl -tag -width indent 2048.It Fl e Ar editor 2049Use the editor named by 2050.Ar editor 2051to edit the commands. 2052The 2053.Ar editor 2054string is a command name, 2055subject to search via the 2056.Va PATH 2057variable. 2058The value in the 2059.Va FCEDIT 2060variable is used as a default when 2061.Fl e 2062is not specified. 2063If 2064.Va FCEDIT 2065is null or unset, the value of the 2066.Va EDITOR 2067variable is used. 2068If 2069.Va EDITOR 2070is null or unset, 2071.Xr ed 1 2072is used as the editor. 2073.It Fl l No (ell) 2074List the commands rather than invoking 2075an editor on them. 2076The commands are written in the 2077sequence indicated by the 2078.Ar first 2079and 2080.Ar last 2081operands, as affected by 2082.Fl r , 2083with each command preceded by the command number. 2084.It Fl n 2085Suppress command numbers when listing with 2086.Fl l . 2087.It Fl r 2088Reverse the order of the commands listed 2089(with 2090.Fl l ) 2091or edited 2092(with neither 2093.Fl l 2094nor 2095.Fl s ) . 2096.It Fl s 2097Re-execute the command without invoking an editor. 2098.It Ar first 2099.It Ar last 2100Select the commands to list or edit. 2101The number of previous commands that can be accessed 2102are determined by the value of the 2103.Va HISTSIZE 2104variable. 2105The value of 2106.Ar first 2107or 2108.Ar last 2109or both are one of the following: 2110.Bl -tag -width indent 2111.It Oo Cm + Oc Ns Ar num 2112A positive number representing a command number; 2113command numbers can be displayed with the 2114.Fl l 2115option. 2116.It Fl Ar num 2117A negative decimal number representing the 2118command that was executed 2119.Ar num 2120of 2121commands previously. 2122For example, \-1 is the immediately previous command. 2123.It Ar string 2124A string indicating the most recently entered command 2125that begins with that string. 2126If the 2127.Ar old Ns = Ns Ar new 2128operand is not also specified with 2129.Fl s , 2130the string form of the first operand cannot contain an embedded equal sign. 2131.El 2132.El 2133.Pp 2134The following variables affect the execution of 2135.Ic fc : 2136.Bl -tag -width ".Va HISTSIZE" 2137.It Va FCEDIT 2138Name of the editor to use for history editing. 2139.It Va HISTSIZE 2140The number of previous commands that are accessible. 2141.El 2142.It Ic fg Op Ar job 2143Move the specified 2144.Ar job 2145or the current job to the foreground. 2146.It Ic getopts Ar optstring var 2147The 2148.Tn POSIX 2149.Ic getopts 2150command. 2151The 2152.Ic getopts 2153command deprecates the older 2154.Xr getopt 1 2155command. 2156The first argument should be a series of letters, each possibly 2157followed by a colon which indicates that the option takes an argument. 2158The specified variable is set to the parsed option. 2159The index of 2160the next argument is placed into the shell variable 2161.Va OPTIND . 2162If an option takes an argument, it is placed into the shell variable 2163.Va OPTARG . 2164If an invalid option is encountered, 2165.Ar var 2166is set to 2167.Ql \&? . 2168It returns a false value (1) when it encounters the end of the options. 2169.It Ic hash Oo Fl rv Oc Op Ar command ... 2170The shell maintains a hash table which remembers the locations of commands. 2171With no arguments whatsoever, the 2172.Ic hash 2173command prints out the contents of this table. 2174Entries which have not been looked at since the last 2175.Ic cd 2176command are marked with an asterisk; 2177it is possible for these entries to be invalid. 2178.Pp 2179With arguments, the 2180.Ic hash 2181command removes each specified 2182.Ar command 2183from the hash table (unless they are functions) and then locates it. 2184With the 2185.Fl v 2186option, 2187.Ic hash 2188prints the locations of the commands as it finds them. 2189The 2190.Fl r 2191option causes the 2192.Ic hash 2193command to delete all the entries in the hash table except for functions. 2194.It Ic jobid Op Ar job 2195Print the process IDs of the processes in the specified 2196.Ar job . 2197If the 2198.Ar job 2199argument is omitted, use the current job. 2200.It Ic jobs Oo Fl lps Oc Op Ar job ... 2201Print information about the specified jobs, or all jobs if no 2202.Ar job 2203argument is given. 2204The information printed includes job ID, status and command name. 2205.Pp 2206If the 2207.Fl l 2208option is specified, the PID of each job is also printed. 2209If the 2210.Fl p 2211option is specified, only the process IDs for the process group leaders 2212are printed, one per line. 2213If the 2214.Fl s 2215option is specified, only the PIDs of the job commands are printed, one per 2216line. 2217.It Ic kill 2218A built-in equivalent of 2219.Xr kill 1 2220that additionally supports sending signals to jobs. 2221.It Ic local Oo Ar variable ... Oc Op Fl 2222See the 2223.Sx Functions 2224subsection. 2225.It Ic printf 2226A built-in equivalent of 2227.Xr printf 1 . 2228.It Ic pwd Op Fl L | P 2229Print the path of the current directory. 2230The built-in command may 2231differ from the program of the same name because the 2232built-in command remembers what the current directory 2233is rather than recomputing it each time. 2234This makes 2235it faster. 2236However, if the current directory is 2237renamed, 2238the built-in version of 2239.Xr pwd 1 2240will continue to print the old name for the directory. 2241.Pp 2242If the 2243.Fl P 2244option is specified, symbolic links are resolved. 2245If the 2246.Fl L 2247option is specified, the shell's notion of the current directory 2248is printed (symbolic links are not resolved). 2249This is the default. 2250.It Ic read Oo Fl p Ar prompt Oc Oo 2251.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2252The 2253.Ar prompt 2254is printed if the 2255.Fl p 2256option is specified 2257and the standard input is a terminal. 2258Then a line is 2259read from the standard input. 2260The trailing newline 2261is deleted from the line and the line is split as 2262described in the section on 2263.Sx White Space Splitting (Field Splitting) 2264above, and 2265the pieces are assigned to the variables in order. 2266If there are more pieces than variables, the remaining 2267pieces (along with the characters in 2268.Va IFS 2269that separated them) 2270are assigned to the last variable. 2271If there are more variables than pieces, the remaining 2272variables are assigned the null string. 2273.Pp 2274Backslashes are treated specially, unless the 2275.Fl r 2276option is 2277specified. 2278If a backslash is followed by 2279a newline, the backslash and the newline will be 2280deleted. 2281If a backslash is followed by any other 2282character, the backslash will be deleted and the following 2283character will be treated as though it were not in 2284.Va IFS , 2285even if it is. 2286.Pp 2287If the 2288.Fl t 2289option is specified and the 2290.Ar timeout 2291elapses before a complete line of input is supplied, 2292the 2293.Ic read 2294command will return an exit status of 1 without assigning any values. 2295The 2296.Ar timeout 2297value may optionally be followed by one of 2298.Ql s , 2299.Ql m 2300or 2301.Ql h 2302to explicitly specify seconds, minutes or hours. 2303If none is supplied, 2304.Ql s 2305is assumed. 2306.Pp 2307The 2308.Fl e 2309option exists only for backward compatibility with older scripts. 2310.It Ic readonly Oo Fl p Oc Op Ar name ... 2311Each specified 2312.Ar name 2313is marked as read only, 2314so that it cannot be subsequently modified or unset. 2315The shell allows the value of a variable to be set 2316at the same time as it is marked read only 2317by using the following form: 2318.Pp 2319.D1 Ic readonly Ar name Ns = Ns Ar value 2320.Pp 2321With no arguments the 2322.Ic readonly 2323command lists the names of all read only variables. 2324If the 2325.Fl p 2326option is specified, the read-only variables are printed as 2327.Dq Ic readonly Ar name Ns = Ns Ar value 2328lines, suitable for re-input to the shell. 2329.It Ic return Op Ar exitstatus 2330See the 2331.Sx Functions 2332subsection. 2333.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 2334.Fl c Ar string Oc Op Fl - Ar arg ... 2335The 2336.Ic set 2337command performs three different functions: 2338.Bl -item 2339.It 2340With no arguments, it lists the values of all shell variables. 2341.It 2342If options are given, 2343either in short form or using the long 2344.Dq Fl /+o Ar longname 2345form, 2346it sets or clears the specified options as described in the section called 2347.Sx Argument List Processing . 2348.It 2349If the 2350.Dq Fl - 2351option is specified, 2352.Ic set 2353will replace the shell's positional parameters with the subsequent 2354arguments. 2355If no arguments follow the 2356.Dq Fl - 2357option, 2358all the positional parameters will be cleared, 2359which is equivalent to executing the command 2360.Dq Li "shift $#" . 2361The 2362.Dq Fl - 2363flag may be omitted when specifying arguments to be used 2364as positional replacement parameters. 2365This is not recommended, 2366because the first argument may begin with a dash 2367.Pq Ql - 2368or a plus 2369.Pq Ql + , 2370which the 2371.Ic set 2372command will interpret as a request to enable or disable options. 2373.El 2374.It Ic setvar Ar variable value 2375Assigns the specified 2376.Ar value 2377to the specified 2378.Ar variable . 2379The 2380.Ic setvar 2381command is intended to be used in functions that 2382assign values to variables whose names are passed as parameters. 2383In general it is better to write 2384.Dq Ar variable Ns = Ns Ar value 2385rather than using 2386.Ic setvar . 2387.It Ic shift Op Ar n 2388Shift the positional parameters 2389.Ar n 2390times, or once if 2391.Ar n 2392is not specified. 2393A shift sets the value of 2394.Li $1 2395to the value of 2396.Li $2 , 2397the value of 2398.Li $2 2399to the value of 2400.Li $3 , 2401and so on, 2402decreasing the value of 2403.Li $# 2404by one. 2405If there are zero positional parameters, shifting does not do anything. 2406.It Ic test 2407A built-in equivalent of 2408.Xr test 1 . 2409.It Ic times 2410Print the amount of time spent executing the shell process and its children. 2411The first output line shows the user and system times for the shell process 2412itself, the second one contains the user and system times for the 2413children. 2414.It Ic trap Oo Ar action Oc Ar signal ... 2415.It Ic trap Fl l 2416Cause the shell to parse and execute 2417.Ar action 2418when any specified 2419.Ar signal 2420is received. 2421The signals are specified by name or number. 2422In addition, the pseudo-signal 2423.Cm EXIT 2424may be used to specify an 2425.Ar action 2426that is performed when the shell terminates. 2427The 2428.Ar action 2429may be an empty string or a dash 2430.Pq Ql - ; 2431the former causes the specified signal to be ignored 2432and the latter causes the default action to be taken. 2433Omitting the 2434.Ar action 2435is another way to request the default action, for compatibility reasons this 2436usage is not recommended though. 2437In a subshell or utility environment, 2438the shell resets trapped (but not ignored) signals to the default action. 2439The 2440.Ic trap 2441command has no effect on signals that were ignored on entry to the shell. 2442.Pp 2443Option 2444.Fl l 2445causes the 2446.Ic trap 2447command to display a list of valid signal names. 2448.It Ic true 2449A null command that returns a 0 (true) exit value. 2450.It Ic type Op Ar name ... 2451Interpret each 2452.Ar name 2453as a command and print the resolution of the command search. 2454Possible resolutions are: 2455shell keyword, alias, special shell builtin, shell builtin, command, 2456tracked alias 2457and not found. 2458For aliases the alias expansion is printed; 2459for commands and tracked aliases 2460the complete pathname of the command is printed. 2461.It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit 2462Set or display resource limits (see 2463.Xr getrlimit 2 ) . 2464If 2465.Ar limit 2466is specified, the named resource will be set; 2467otherwise the current resource value will be displayed. 2468.Pp 2469If 2470.Fl H 2471is specified, the hard limits will be set or displayed. 2472While everybody is allowed to reduce a hard limit, 2473only the superuser can increase it. 2474The 2475.Fl S 2476option 2477specifies the soft limits instead. 2478When displaying limits, 2479only one of 2480.Fl S 2481or 2482.Fl H 2483can be given. 2484The default is to display the soft limits, 2485and to set both the hard and the soft limits. 2486.Pp 2487Option 2488.Fl a 2489causes the 2490.Ic ulimit 2491command to display all resources. 2492The parameter 2493.Ar limit 2494is not acceptable in this mode. 2495.Pp 2496The remaining options specify which resource value is to be 2497displayed or modified. 2498They are mutually exclusive. 2499.Bl -tag -width indent 2500.It Fl b Ar sbsize 2501The maximum size of socket buffer usage, in bytes. 2502.It Fl c Ar coredumpsize 2503The maximal size of core dump files, in 512-byte blocks. 2504.It Fl d Ar datasize 2505The maximal size of the data segment of a process, in kilobytes. 2506.It Fl f Ar filesize 2507The maximal size of a file, in 512-byte blocks. 2508.It Fl l Ar lockedmem 2509The maximal size of memory that can be locked by a process, in 2510kilobytes. 2511.It Fl m Ar memoryuse 2512The maximal resident set size of a process, in kilobytes. 2513.It Fl n Ar nofiles 2514The maximal number of descriptors that could be opened by a process. 2515.It Fl s Ar stacksize 2516The maximal size of the stack segment, in kilobytes. 2517.It Fl t Ar time 2518The maximal amount of CPU time to be used by each process, in seconds. 2519.It Fl u Ar userproc 2520The maximal number of simultaneous processes for this user ID. 2521.It Fl v Ar virtualmem 2522The maximal virtual size of a process, in kilobytes. 2523.El 2524.It Ic umask Oo Fl S Oc Op Ar mask 2525Set the file creation mask (see 2526.Xr umask 2 ) 2527to the octal or symbolic (see 2528.Xr chmod 1 ) 2529value specified by 2530.Ar mask . 2531If the argument is omitted, the current mask value is printed. 2532If the 2533.Fl S 2534option is specified, the output is symbolic, otherwise the output is octal. 2535.It Ic unalias Oo Fl a Oc Op Ar name ... 2536The specified alias names are removed. 2537If 2538.Fl a 2539is specified, all aliases are removed. 2540.It Ic unset Oo Fl fv Oc Ar name ... 2541The specified variables or functions are unset and unexported. 2542If the 2543.Fl v 2544option is specified or no options are given, the 2545.Ar name 2546arguments are treated as variable names. 2547If the 2548.Fl f 2549option is specified, the 2550.Ar name 2551arguments are treated as function names. 2552.It Ic wait Op Ar job 2553Wait for the specified 2554.Ar job 2555to complete and return the exit status of the last process in the 2556.Ar job . 2557If the argument is omitted, wait for all jobs to complete 2558and return an exit status of zero. 2559.El 2560.Ss Commandline Editing 2561When 2562.Nm 2563is being used interactively from a terminal, the current command 2564and the command history 2565(see 2566.Ic fc 2567in 2568.Sx Built-in Commands ) 2569can be edited using 2570.Nm vi Ns -mode 2571command line editing. 2572This mode uses commands similar 2573to a subset of those described in the 2574.Xr vi 1 2575man page. 2576The command 2577.Dq Li "set -o vi" 2578(or 2579.Dq Li "set -V" ) 2580enables 2581.Nm vi Ns -mode 2582editing and places 2583.Nm 2584into 2585.Nm vi 2586insert mode. 2587With 2588.Nm vi Ns -mode 2589enabled, 2590.Nm 2591can be switched between insert mode and command mode by typing 2592.Aq ESC . 2593Hitting 2594.Aq return 2595while in command mode will pass the line to the shell. 2596.Pp 2597Similarly, the 2598.Dq Li "set -o emacs" 2599(or 2600.Dq Li "set -E" ) 2601command can be used to enable a subset of 2602.Nm emacs Ns -style 2603command line editing features. 2604.Sh ENVIRONMENT 2605The following environment variables affect the execution of 2606.Nm : 2607.Bl -tag -width ".Ev LANGXXXXXX" 2608.It Ev ENV 2609Initialization file for interactive shells. 2610.It Ev LANG , Ev LC_* 2611Locale settings. 2612These are inherited by children of the shell, 2613and is used in a limited manner by the shell itself. 2614.It Ev PWD 2615An absolute pathname for the current directory, 2616possibly containing symbolic links. 2617This is used and updated by the shell. 2618.It Ev TERM 2619The default terminal setting for the shell. 2620This is inherited by children of the shell, and is used in the history 2621editing modes. 2622.El 2623.Pp 2624Additionally, all environment variables are turned into shell variables 2625at startup, 2626which may affect the shell as described under 2627.Sx Special Variables . 2628.Sh EXIT STATUS 2629Errors that are detected by the shell, such as a syntax error, will 2630cause the shell to exit with a non-zero exit status. 2631If the shell is not an interactive shell, the execution of the shell 2632file will be aborted. 2633Otherwise the shell will return the exit status of the last command 2634executed, or if the 2635.Ic exit 2636builtin is used with a numeric argument, it 2637will return the argument. 2638.Sh SEE ALSO 2639.Xr builtin 1 , 2640.Xr chsh 1 , 2641.Xr echo 1 , 2642.Xr ed 1 , 2643.Xr emacs 1 Pq Pa pkgsrc/editors/emacs , 2644.Xr kill 1 , 2645.Xr printf 1 , 2646.Xr pwd 1 , 2647.Xr test 1 , 2648.Xr vi 1 , 2649.Xr execve 2 , 2650.Xr getrlimit 2 , 2651.Xr umask 2 , 2652.Xr wctype 3 , 2653.Xr editrc 5 , 2654.Xr script 7 2655.Sh HISTORY 2656A 2657.Nm 2658command, the Thompson shell, appeared in 2659.At v1 . 2660It was superseded in 2661.At v7 2662by the Bourne shell, which inherited the name 2663.Nm . 2664.Pp 2665This version of 2666.Nm 2667was rewritten in 1989 under the 2668.Bx 2669license after the Bourne shell from 2670.At V.4 . 2671.Sh AUTHORS 2672This version of 2673.Nm 2674was originally written by 2675.An Kenneth Almquist . 2676.Sh BUGS 2677The 2678.Nm 2679utility does not recognize multibyte characters other than UTF-8. 2680Splitting using 2681.Va IFS 2682and the line editing library 2683.Xr editline 3 2684do not recognize multibyte characters. 2685.Pp 2686The characters generated by filename completion should probably be quoted 2687to ensure that the filename is still valid after the input line has been 2688processed. 2689