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 1.124 2006/10/07 16:51:16 stefanf Exp $ 38.\" $DragonFly: src/bin/sh/sh.1,v 1.14 2008/09/15 20:24:41 thomas Exp $ 39.\" 40.Dd February 8, 2009 41.Dt SH 1 42.Os 43.Sh NAME 44.Nm sh 45.Nd command interpreter (shell) 46.Sh SYNOPSIS 47.Nm 48.Op Fl /+abCEefIimnPpsTuVvx 49.Op Fl /+o Ar longname 50.Op Fl c Ar string 51.Op Ar arg ... 52.Sh DESCRIPTION 53The 54.Nm 55utility is the standard command interpreter for the system. 56The current version of 57.Nm 58is in the process of being changed to 59conform with the 60.St -p1003.2 61specification for the shell. 62This version has many features which make 63it appear 64similar in some respects to the Korn shell, but it is not a Korn 65shell clone like pdksh. 66Only features 67designated by POSIX, plus a few Berkeley extensions, are being 68incorporated into this shell. 69This man page is not intended to be a tutorial nor a complete 70specification of the shell. 71.Ss Overview 72The shell is a command that reads lines from 73either a file or the terminal, interprets them, and 74generally executes other commands. 75It is the program that is started when a user logs into the system, 76although a user can select a different shell with the 77.Xr chsh 1 78command. 79The shell 80implements a language that has flow control constructs, 81a macro facility that provides a variety of features in 82addition to data storage, along with built-in history and line 83editing capabilities. 84It incorporates many features to 85aid interactive use and has the advantage that the interpretative 86language is common to both interactive and non-interactive 87use (shell scripts). 88That is, commands can be typed directly 89to the running shell or can be put into a file, 90which can be executed directly by the shell. 91.Ss Invocation 92.\" 93.\" XXX This next sentence is incredibly confusing. 94.\" 95If no arguments are present and if the standard input of the shell 96is connected to a terminal 97(or if the 98.Fl i 99option is set), 100the shell is considered an interactive shell. 101An interactive shell 102generally prompts before each command and handles programming 103and command errors differently (as described below). 104When first starting, the shell inspects argument 0, and 105if it begins with a dash 106.Pq Ql - , 107the shell is also considered a login shell. 108This is normally done automatically by the system 109when the user first logs in. 110A login shell first reads commands 111from the files 112.Pa /etc/profile 113and then 114.Pa .profile 115if they exist. 116If the environment variable 117.Ev ENV 118is set on entry to a shell, or is set in the 119.Pa .profile 120of a login shell, the shell then reads commands from the file named in 121.Ev ENV . 122Therefore, a user should place commands that are to be executed only 123at login time in the 124.Pa .profile 125file, and commands that are executed for every shell inside the 126.Ev ENV 127file. 128The user can set the 129.Ev ENV 130variable to some file by placing the following line in the file 131.Pa .profile 132in the home directory, 133substituting for 134.Pa .shinit 135the filename desired: 136.Pp 137.Dl ENV=$HOME/.shinit; export ENV 138.Pp 139The first non-option argument specified on the command line 140will be treated as the 141name of a file from which to read commands (a shell script), and 142the remaining arguments are set as the positional parameters 143of the shell ($1, $2, etc). 144Otherwise, the shell reads commands 145from its standard input. 146.Pp 147Unlike older versions of 148.Nm 149the 150.Ev ENV 151script is only sourced on invocation of interactive shells. 152This 153closes a well-known, and sometimes easily exploitable security 154hole related to poorly thought out 155.Ev ENV 156scripts. 157.Ss Argument List Processing 158All of the single letter options to 159.Nm 160have a corresponding long name, 161with the exception of 162.Fl c 163and 164.Fl /+o . 165These long names are provided next to the single letter options 166in the descriptions below. 167The long name for an option may be specified as an argument to the 168.Fl /+o 169option of 170.Nm . 171Once the shell is running, 172the long name for an option may be specified as an argument to the 173.Fl /+o 174option of the 175.Ic set 176built-in command 177(described later in the section called 178.Sx Built-in Commands ) . 179Introducing an option with a dash 180.Pq Ql - 181enables the option, 182while using a plus 183.Pq Ql + 184disables the option. 185A 186.Dq Li -- 187or plain 188.Ql - 189will stop option processing and will force the remaining 190words on the command line to be treated as arguments. 191The 192.Fl /+o 193and 194.Fl c 195options do not have long names. 196They take arguments and are described after the single letter options. 197.Bl -tag -width indent 198.It Fl a Li allexport 199Flag variables for export when assignments are made to them. 200.It Fl b Li notify 201Enable asynchronous notification of background job 202completion. 203(UNIMPLEMENTED) 204.It Fl C Li noclobber 205Do not overwrite existing files with 206.Ql > . 207.It Fl E Li emacs 208Enable the built-in 209.Xr emacs 1 210command line editor (disables the 211.Fl V 212option if it has been set). 213.It Fl e Li errexit 214Exit immediately if any untested command fails in non-interactive mode. 215The exit status of a command is considered to be 216explicitly tested if the command is part of the list used to control 217an 218.Ic if , elif , while , 219or 220.Ic until ; 221if the command is the left 222hand operand of an 223.Dq Li && 224or 225.Dq Li || 226operator; or if the command is a pipeline preceded by the 227.Ic !\& 228operator. 229If a shell function is executed and its exit status is explicitly 230tested, all commands of the function are considered to be tested as 231well. 232.It Fl f Li noglob 233Disable pathname expansion. 234.It Fl I Li ignoreeof 235Ignore 236.Dv EOF Ns ' Ns s 237from input when in interactive mode. 238.It Fl i Li interactive 239Force the shell to behave interactively. 240.It Fl m Li monitor 241Turn on job control (set automatically when interactive). 242.It Fl n Li noexec 243If not interactive, read commands but do not 244execute them. 245This is useful for checking the 246syntax of shell scripts. 247.It Fl P Li physical 248Change the default for the 249.Ic cd 250and 251.Ic pwd 252commands from 253.Fl L 254(logical directory layout) 255to 256.Fl P 257(physical directory layout). 258.It Fl p Li privileged 259Turn on privileged mode. 260This mode is enabled on startup 261if either the effective user or group id is not equal to the 262real user or group id. 263Turning this mode off sets the 264effective user and group ids to the real user and group ids. 265When this mode is enabled for interactive shells, the file 266.Pa /etc/suid_profile 267is sourced instead of 268.Pa ~/.profile 269after 270.Pa /etc/profile 271is sourced, and the contents of the 272.Ev ENV 273variable are ignored. 274.It Fl s Li stdin 275Read commands from standard input (set automatically 276if no file arguments are present). 277This option has 278no effect when set after the shell has already started 279running (i.e., when set with the 280.Ic set 281command). 282.It Fl T Li trapsasync 283When waiting for a child, execute traps immediately. 284If this option is not set, 285traps are executed after the child exits, 286as specified in 287.St -p1003.2 . 288This nonstandard option is useful for putting guarding shells around 289children that block signals. 290The surrounding shell may kill the child 291or it may just return control to the tty and leave the child alone, 292like this: 293.Bd -literal -offset indent 294sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 295.Ed 296.Pp 297.It Fl u Li nounset 298Write a message to standard error when attempting 299to expand a variable that is not set, and if the 300shell is not interactive, exit immediately. 301.It Fl V Li vi 302Enable the built-in 303.Xr vi 1 304command line editor (disables 305.Fl E 306if it has been set). 307.It Fl v Li verbose 308The shell writes its input to standard error 309as it is read. 310Useful for debugging. 311.It Fl x Li xtrace 312Write each command 313(preceded by the value of the 314.Ev PS4 315variable) 316to standard error before it is executed. 317Useful for debugging. 318.It "\ \ " Em tabcomplete 319Enables filename completion in the command line editor. 320Typing a tab character will extend the current input word to match a 321filename. 322If more than one filename matches it is only extended to be the common prefix. 323Typing a second tab character will list all the matching names. 324Turned on by default in an interactive shell. 325.El 326.Pp 327The 328.Fl c 329option causes the commands to be read from the 330.Ar string 331operand instead of from the standard input. 332Keep in mind that this option only accepts a single string as its 333argument, hence multi-word strings must be quoted. 334.Pp 335The 336.Fl /+o 337option takes as its only argument the long name of an option 338to be enabled or disabled. 339For example, the following two invocations of 340.Nm 341both enable the built-in 342.Xr emacs 1 343command line editor: 344.Bd -literal -offset indent 345set -E 346set -o emacs 347.Ed 348.Pp 349If used without an argument, the 350.Fl o 351option displays the current option settings in a human-readable format. 352If 353.Cm +o 354is used without an argument, the current option settings are output 355in a format suitable for re-input into the shell. 356.Ss Lexical Structure 357The shell reads input in terms of lines from a file and breaks 358it up into words at whitespace (blanks and tabs), and at 359certain sequences of 360characters called 361.Dq operators , 362which are special to the shell. 363There are two types of operators: control operators and 364redirection operators (their meaning is discussed later). 365The following is a list of valid operators: 366.Bl -tag -width indent 367.It Control operators: 368.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 369.It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en 370.It Li ;; Ta Li ; Ta Li | Ta Li || 371.El 372.It Redirection operators: 373.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 374.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 375.It Li <& Ta Li >& Ta Li <<- Ta Li >| 376.El 377.El 378.Pp 379The character 380.Ql # 381introduces a comment if used at the beginning of a word. 382The word starting with 383.Ql # 384and the rest of the line are ignored. 385.Ss Quoting 386Quoting is used to remove the special meaning of certain characters 387or words to the shell, such as operators, whitespace, keywords, 388or alias names. 389.Pp 390There are three types of quoting: matched single quotes, 391matched double quotes, and backslash. 392.Bl -tag -width indent 393.It Single Quotes 394Enclosing characters in single quotes preserves the literal 395meaning of all the characters (except single quotes, making 396it impossible to put single-quotes in a single-quoted string). 397.It Double Quotes 398Enclosing characters within double quotes preserves the literal 399meaning of all characters except dollarsign 400.Pq Ql $ , 401backquote 402.Pq Ql ` , 403and backslash 404.Pq Ql \e . 405The backslash inside double quotes is historically weird. 406It remains literal unless it precedes the following characters, 407which it serves to quote: 408.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 409.It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en 410.El 411.It Backslash 412A backslash preserves the literal meaning of the following 413character, with the exception of the newline character 414.Pq Ql \en . 415A backslash preceding a newline is treated as a line continuation. 416.El 417.Ss Reserved Words 418Reserved words are words that have special meaning to the 419shell and are recognized at the beginning of a line and 420after a control operator. 421The following are reserved words: 422.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 423.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 424.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 425.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 426.El 427.Ss Aliases 428An alias is a name and corresponding value set using the 429.Ic alias 430built-in command. 431Whenever a reserved word may occur (see above), 432and after checking for reserved words, the shell 433checks the word to see if it matches an alias. 434If it does, it replaces it in the input stream with its value. 435For example, if there is an alias called 436.Dq Li lf 437with the value 438.Dq Li ls -F , 439then the input 440.Bd -literal -offset indent 441lf foobar 442.Ed 443.Pp 444would become 445.Bd -literal -offset indent 446ls -F foobar 447.Ed 448.Pp 449Aliases provide a convenient way for naive users to 450create shorthands for commands without having to learn how 451to create functions with arguments. 452They can also be 453used to create lexically obscure code. 454This use is discouraged. 455.Pp 456An alias name may be escaped in a command line, so that it is not 457replaced by its alias value, by using quoting characters within or 458adjacent to the alias name. 459This is most often done by prefixing 460an alias name with a backslash to execute a function, built-in, or 461normal program with the same name. 462See the 463.Sx Quoting 464subsection. 465.Ss Commands 466The shell interprets the words it reads according to a 467language, the specification of which is outside the scope 468of this man page (refer to the BNF in the 469.St -p1003.2 470document). 471Essentially though, a line is read and if 472the first word of the line (or after a control operator) 473is not a reserved word, then the shell has recognized a 474simple command. 475Otherwise, a complex command or some 476other special construct may have been recognized. 477.Ss Simple Commands 478If a simple command has been recognized, the shell performs 479the following actions: 480.Bl -enum 481.It 482Leading words of the form 483.Dq Li name=value 484are stripped off and assigned to the environment of 485the simple command. 486Redirection operators and 487their arguments (as described below) are stripped 488off and saved for processing. 489.It 490The remaining words are expanded as described in 491the section called 492.Sx Word Expansions , 493and the first remaining word is considered the command 494name and the command is located. 495The remaining 496words are considered the arguments of the command. 497If no command name resulted, then the 498.Dq Li name=value 499variable assignments recognized in 1) affect the 500current shell. 501.It 502Redirections are performed as described in 503the next section. 504.El 505.Ss Redirections 506Redirections are used to change where a command reads its input 507or sends its output. 508In general, redirections open, close, or 509duplicate an existing reference to a file. 510The overall format 511used for redirection is: 512.Pp 513.Dl [n] redir-op file 514.Pp 515The 516.Ql redir-op 517is one of the redirection operators mentioned 518previously. 519The following gives some examples of how these 520operators can be used. 521Note that stdin and stdout are commonly used abbreviations 522for standard input and standard output respectively. 523.Bl -tag -width "1234567890XX" -offset indent 524.It Li [n]> file 525redirect stdout (or file descriptor n) to file 526.It Li [n]>| file 527same as above, but override the 528.Fl C 529option 530.It Li [n]>> file 531append stdout (or file descriptor n) to file 532.It Li [n]< file 533redirect stdin (or file descriptor n) from file 534.It Li [n]<> file 535redirect stdin (or file descriptor n) to and from file 536.It Li [n1]<&n2 537duplicate stdin (or file descriptor n1) from file descriptor n2 538.It Li [n]<&- 539close stdin (or file descriptor n) 540.It Li [n1]>&n2 541duplicate stdout (or file descriptor n1) to file descriptor n2 542.It Li [n]>&- 543close stdout (or file descriptor n) 544.El 545.Pp 546The following redirection is often called a 547.Dq here-document . 548.Bd -literal -offset indent 549[n]<< delimiter 550 here-doc-text 551 ... 552delimiter 553.Ed 554.Pp 555All the text on successive lines up to the delimiter is 556saved away and made available to the command on standard 557input, or file descriptor n if it is specified. 558If the delimiter 559as specified on the initial line is quoted, then the here-doc-text 560is treated literally, otherwise the text is subjected to 561parameter expansion, command substitution, and arithmetic 562expansion (as described in the section on 563.Sx Word Expansions ) . 564If the operator is 565.Dq Li <<- 566instead of 567.Dq Li << , 568then leading tabs 569in the here-doc-text are stripped. 570.Ss Search and Execution 571There are three types of commands: shell functions, 572built-in commands, and normal programs. 573The command is searched for (by name) in that order. 574The three types of commands are all executed in a different way. 575.Pp 576When a shell function is executed, all of the shell positional 577parameters (except $0, which remains unchanged) are 578set to the arguments of the shell function. 579The variables which are explicitly placed in the environment of 580the command (by placing assignments to them before the 581function name) are made local to the function and are set 582to the values given. 583Then the command given in the function definition is executed. 584The positional parameters are restored to their original values 585when the command completes. 586This all occurs within the current shell. 587.Pp 588Shell built-in commands are executed internally to the shell, without 589spawning a new process. 590.Pp 591Otherwise, if the command name does not match a function 592or built-in command, the command is searched for as a normal 593program in the file system (as described in the next section). 594When a normal program is executed, the shell runs the program, 595passing the arguments and the environment to the program. 596If the program is not a normal executable file 597(i.e., if it does not begin with the 598.Qq magic number 599whose 600.Tn ASCII 601representation is 602.Qq #! , 603resulting in an 604.Er ENOEXEC 605return value from 606.Xr execve 2 ) 607the shell will interpret the program in a subshell. 608The child shell will reinitialize itself in this case, 609so that the effect will be 610as if a new shell had been invoked to handle the ad-hoc shell script, 611except that the location of hashed commands located in 612the parent shell will be remembered by the child. 613.Pp 614Note that previous versions of this document 615and the source code itself misleadingly and sporadically 616refer to a shell script without a magic number 617as a 618.Qq shell procedure . 619.Ss Path Search 620When locating a command, the shell first looks to see if 621it has a shell function by that name. 622Then it looks for a 623built-in command by that name. 624If a built-in command is not found, 625one of two things happen: 626.Bl -enum 627.It 628Command names containing a slash are simply executed without 629performing any searches. 630.It 631The shell searches each entry in 632.Ev PATH 633in turn for the command. 634The value of the 635.Ev PATH 636variable should be a series of 637entries separated by colons. 638Each entry consists of a 639directory name. 640The current directory 641may be indicated implicitly by an empty directory name, 642or explicitly by a single period. 643.El 644.Ss Command Exit Status 645Each command has an exit status that can influence the behavior 646of other shell commands. 647The paradigm is that a command exits 648with zero for normal or success, and non-zero for failure, 649error, or a false indication. 650The man page for each command 651should indicate the various exit codes and what they mean. 652Additionally, the built-in commands return exit codes, as does 653an executed shell function. 654.Pp 655If a command is terminated by a signal, its exit status is 128 plus 656the signal number. 657Signal numbers are defined in the header file 658.In sys/signal.h . 659.Ss Complex Commands 660Complex commands are combinations of simple commands 661with control operators or reserved words, together creating a larger complex 662command. 663More generally, a command is one of the following: 664.Bl -item -offset indent 665.It 666simple command 667.It 668pipeline 669.It 670list or compound-list 671.It 672compound command 673.It 674function definition 675.El 676.Pp 677Unless otherwise stated, the exit status of a command is 678that of the last simple command executed by the command. 679.Ss Pipelines 680A pipeline is a sequence of one or more commands separated 681by the control operator |. 682The standard output of all but 683the last command is connected to the standard input 684of the next command. 685The standard output of the last 686command is inherited from the shell, as usual. 687.Pp 688The format for a pipeline is: 689.Pp 690.Dl [!] command1 [ | command2 ...] 691.Pp 692The standard output of command1 is connected to the standard 693input of command2. 694The standard input, standard output, or 695both of a command is considered to be assigned by the 696pipeline before any redirection specified by redirection 697operators that are part of the command. 698.Pp 699If the pipeline is not in the background (discussed later), 700the shell waits for all commands to complete. 701.Pp 702If the reserved word 703.Ic !\& 704does not precede the pipeline, the 705exit status is the exit status of the last command specified 706in the pipeline. 707Otherwise, the exit status is the logical 708NOT of the exit status of the last command. 709That is, if 710the last command returns zero, the exit status is 1; if 711the last command returns greater than zero, the exit status 712is zero. 713.Pp 714Because pipeline assignment of standard input or standard 715output or both takes place before redirection, it can be 716modified by redirection. 717For example: 718.Pp 719.Dl $ command1 2>&1 | command2 720.Pp 721sends both the standard output and standard error of 722.Ql command1 723to the standard input of 724.Ql command2 . 725.Pp 726A 727.Ql \&; 728or newline terminator causes the preceding 729AND-OR-list 730(described below in the section called 731.Sx Short-Circuit List Operators ) 732to be executed sequentially; 733an 734.Ql & 735causes asynchronous execution of the preceding AND-OR-list. 736.Pp 737Note that unlike some other shells, 738.Nm 739executes each process in the pipeline as a child of the 740.Nm 741process. 742Shell built-in commands are the exception to this rule. 743They are executed in the current shell, although they do not affect its 744environment when used in pipelines. 745.Ss Background Commands (&) 746If a command is terminated by the control operator ampersand 747.Pq Ql & , 748the shell executes the command asynchronously; 749the shell does not wait for the command to finish 750before executing the next command. 751.Pp 752The format for running a command in background is: 753.Bd -literal -offset indent 754command1 & [command2 & ...] 755.Ed 756.Pp 757If the shell is not interactive, the standard input of an 758asynchronous command is set to /dev/null. 759.Ss Lists (Generally Speaking) 760A list is a sequence of zero or more commands separated by 761newlines, semicolons, or ampersands, 762and optionally terminated by one of these three characters. 763The commands in a 764list are executed in the order they are written. 765If command is followed by an ampersand, the shell starts the 766command and immediately proceeds onto the next command; 767otherwise it waits for the command to terminate before 768proceeding to the next one. 769.Ss Short-Circuit List Operators 770.Dq Li && 771and 772.Dq Li || 773are AND-OR list operators. 774.Dq Li && 775executes the first command, and then executes the second command 776if the exit status of the first command is zero. 777.Dq Li || 778is similar, but executes the second command if the exit 779status of the first command is nonzero. 780.Dq Li && 781and 782.Dq Li || 783both have the same priority. 784.Ss Flow-Control Constructs (if, while, for, case) 785The syntax of the 786.Ic if 787command is: 788.\" 789.\" XXX Use .Dl to work around broken handling of .Ic inside .Bd and .Ed . 790.\" 791.Dl Ic if Ar list 792.Dl Ic then Ar list 793.Dl [ Ic elif Ar list 794.Dl Ic then Ar list ] ... 795.Dl [ Ic else Ar list ] 796.Dl Ic fi 797.Pp 798The syntax of the 799.Ic while 800command is: 801.Dl Ic while Ar list 802.Dl Ic do Ar list 803.Dl Ic done 804.Pp 805The two lists are executed repeatedly while the exit status of the 806first list is zero. 807The 808.Ic until 809command is similar, but has the word 810.Ic until 811in place of 812.Ic while , 813which causes it to 814repeat until the exit status of the first list is zero. 815.Pp 816The syntax of the 817.Ic for 818command is: 819.Dl Ic for Ar variable Op Ic in Ar word ... 820.Dl Ic do Ar list 821.Dl Ic done 822.Pp 823If 824.Ic in 825and the following words are omitted, 826.Ic in Li $@ 827is used instead. 828The words are expanded, and then the list is executed 829repeatedly with the variable set to each word in turn. 830The 831.Ic do 832and 833.Ic done 834commands may be replaced with 835.Ql { 836and 837.Ql } . 838.Pp 839The syntax of the 840.Ic break 841and 842.Ic continue 843commands is: 844.Dl Ic break Op Ar num 845.Dl Ic continue Op Ar num 846.Pp 847The 848.Ic break 849command terminates the 850.Ar num 851innermost 852.Ic for 853or 854.Ic while 855loops. 856The 857.Ic continue 858command continues with the next iteration of the innermost loop. 859These are implemented as built-in commands. 860.Pp 861The syntax of the 862.Ic case 863command is 864.Dl Ic case Ar word Ic in 865.Dl pattern) list ;; 866.Dl ... 867.Dl Ic esac 868.Pp 869The pattern can actually be one or more patterns 870(see 871.Sx Shell Patterns 872described later), 873separated by 874.Ql \&| 875characters. 876.Ss Grouping Commands Together 877Commands may be grouped by writing either 878.Bd -literal -offset indent 879(list) 880.Ed 881.Pp 882or 883.Bd -literal -offset indent 884{ list; } 885.Ed 886.Pp 887The first form executes the commands in a subshell. 888Note that built-in commands thus executed do not affect the current shell. 889The second form does not fork another shell, 890so it is slightly more efficient. 891Grouping commands together this way allows the user to 892redirect their output as though they were one program: 893.Bd -literal -offset indent 894{ echo -n "hello"; echo " world"; } > greeting 895.Ed 896.Ss Functions 897The syntax of a function definition is 898.Bd -literal -offset indent 899name ( ) command 900.Ed 901.Pp 902A function definition is an executable statement; when 903executed it installs a function named name and returns an 904exit status of zero. 905The command is normally a list 906enclosed between 907.Ql { 908and 909.Ql } . 910.Pp 911Variables may be declared to be local to a function by 912using the 913.Ic local 914command. 915This should appear as the first statement of a function, 916and the syntax is: 917.Bd -ragged -offset indent 918.Ic local 919.Op Ar variable ... 920.Op Fl 921.Ed 922.Pp 923The 924.Ic local 925command is implemented as a built-in command. 926.Pp 927When a variable is made local, it inherits the initial 928value and exported and readonly flags from the variable 929with the same name in the surrounding scope, if there is 930one. 931Otherwise, the variable is initially unset. 932The shell 933uses dynamic scoping, so that if the variable 934.Em x 935is made local to function 936.Em f , 937which then calls function 938.Em g , 939references to the variable 940.Em x 941made inside 942.Em g 943will refer to the variable 944.Em x 945declared inside 946.Em f , 947not to the global variable named 948.Em x . 949.Pp 950The only special parameter that can be made local is 951.Ql - . 952Making 953.Ql - 954local causes any shell options that are 955changed via the set command inside the function to be 956restored to their original values when the function 957returns. 958.Pp 959The syntax of the 960.Ic return 961command is 962.Bd -ragged -offset indent 963.Ic return 964.Op Ar exitstatus 965.Ed 966.Pp 967It terminates the current executional scope, returning from the previous 968nested function, sourced script, or shell instance, in that order. 969The 970.Ic return 971command is implemented as a built-in command. 972.Ss Variables and Parameters 973The shell maintains a set of parameters. 974A parameter 975denoted by a name is called a variable. 976When starting up, 977the shell turns all the environment variables into shell 978variables. 979New variables can be set using the form 980.Bd -literal -offset indent 981name=value 982.Ed 983.Pp 984Variables set by the user must have a name consisting solely 985of alphabetics, numerics, and underscores. 986The first letter of a variable name must not be numeric. 987A parameter can also be denoted by a number 988or a special character as explained below. 989.Ss Positional Parameters 990A positional parameter is a parameter denoted by a number greater than zero. 991The shell sets these initially to the values of its command line 992arguments that follow the name of the shell script. 993The 994.Ic set 995built-in command can also be used to set or reset them. 996.Ss Special Parameters 997A special parameter is a parameter denoted by a special one-character 998name. 999The special parameters recognized 1000are shown in the following list, exactly as they would appear in input 1001typed by the user or in the source of a shell script. 1002.Bl -hang 1003.It Li $* 1004Expands to the positional parameters, starting from one. 1005When 1006the expansion occurs within a double-quoted string 1007it expands to a single field with the value of each parameter 1008separated by the first character of the 1009.Ev IFS 1010variable, 1011or by a 1012.Aq space 1013if 1014.Ev IFS 1015is unset. 1016.It Li $@ 1017Expands to the positional parameters, starting from one. 1018When 1019the expansion occurs within double-quotes, each positional 1020parameter expands as a separate argument. 1021If there are no positional parameters, the 1022expansion of 1023.Li @ 1024generates zero arguments, even when 1025.Li @ 1026is double-quoted. 1027What this basically means, for example, is 1028if $1 is 1029.Dq abc 1030and $2 is 1031.Dq def ghi , 1032then 1033.Qq Li $@ 1034expands to 1035the two arguments: 1036.Bd -literal -offset indent 1037"abc" "def ghi" 1038.Ed 1039.It Li $# 1040Expands to the number of positional parameters. 1041.It Li $\&? 1042Expands to the exit status of the most recent pipeline. 1043.It Li $- 1044(hyphen) Expands to the current option flags (the single-letter 1045option names concatenated into a string) as specified on 1046invocation, by the set built-in command, or implicitly 1047by the shell. 1048.It Li $$ 1049Expands to the process ID of the invoked shell. 1050A subshell 1051retains the same value of $ as its parent. 1052.It Li $\&! 1053Expands to the process ID of the most recent background 1054command executed from the current shell. 1055For a 1056pipeline, the process ID is that of the last command in the 1057pipeline. 1058.It Li $0 1059(zero) Expands to the name of the shell or shell script. 1060.El 1061.Ss Word Expansions 1062This clause describes the various expansions that are 1063performed on words. 1064Not all expansions are performed on 1065every word, as explained later. 1066.Pp 1067Tilde expansions, parameter expansions, command substitutions, 1068arithmetic expansions, and quote removals that occur within 1069a single word expand to a single field. 1070It is only field 1071splitting or pathname expansion that can create multiple 1072fields from a single word. 1073The single exception to this rule is 1074the expansion of the special parameter 1075.Li @ 1076within double-quotes, 1077as was described above. 1078.Pp 1079The order of word expansion is: 1080.Bl -enum 1081.It 1082Tilde Expansion, Parameter Expansion, Command Substitution, 1083Arithmetic Expansion (these all occur at the same time). 1084.It 1085Field Splitting is performed on fields generated by step (1) 1086unless the 1087.Ev IFS 1088variable is null. 1089.It 1090Pathname Expansion (unless the 1091.Fl f 1092option is in effect). 1093.It 1094Quote Removal. 1095.El 1096.Pp 1097The 1098.Ql $ 1099character is used to introduce parameter expansion, command 1100substitution, or arithmetic evaluation. 1101.Ss Tilde Expansion (substituting a user's home directory) 1102A word beginning with an unquoted tilde character 1103.Pq Ql ~ 1104is 1105subjected to tilde expansion. 1106All the characters up to a slash 1107.Pq Ql / 1108or the end of the word are treated as a username 1109and are replaced with the user's home directory. 1110If the 1111username is missing (as in ~/foobar), the tilde is replaced 1112with the value of the HOME variable (the current user's 1113home directory). 1114.Ss Parameter Expansion 1115The format for parameter expansion is as follows: 1116.Bd -literal -offset indent 1117${expression} 1118.Ed 1119.Pp 1120where expression consists of all characters until the matching 1121.Ql } . 1122Any 1123.Ql } 1124escaped by a backslash or within a quoted string, and characters in 1125embedded arithmetic expansions, command substitutions, and variable 1126expansions, are not examined in determining the matching 1127.Ql } . 1128.Pp 1129The simplest form for parameter expansion is: 1130.Bd -literal -offset indent 1131${parameter} 1132.Ed 1133.Pp 1134The value, if any, of parameter is substituted. 1135.Pp 1136The parameter name or symbol can be enclosed in braces, which are 1137optional except for positional parameters with more than one digit or 1138when parameter is followed by a character that could be interpreted as 1139part of the name. 1140If a parameter expansion occurs inside double-quotes: 1141.Bl -enum 1142.It 1143Pathname expansion is not performed on the results of the 1144expansion. 1145.It 1146Field splitting is not performed on the results of the 1147expansion, with the exception of the special parameter 1148.Li @ . 1149.El 1150.Pp 1151In addition, a parameter expansion can be modified by using one of the 1152following formats. 1153.Bl -tag -width indent 1154.It Li ${parameter:-word} 1155Use Default Values. 1156If parameter is unset or 1157null, the expansion of word is 1158substituted; otherwise, the value of 1159parameter is substituted. 1160.It Li ${parameter:=word} 1161Assign Default Values. 1162If parameter is unset 1163or null, the expansion of word is 1164assigned to parameter. 1165In all cases, the 1166final value of parameter is 1167substituted. 1168Only variables, not positional 1169parameters or special parameters, can be 1170assigned in this way. 1171.It Li ${parameter:?[word]} 1172Indicate Error if Null or Unset. 1173If 1174parameter is unset or null, the expansion of 1175word (or a message indicating it is unset if 1176word is omitted) is written to standard 1177error and the shell exits with a nonzero 1178exit status. 1179Otherwise, the value of 1180parameter is substituted. 1181An 1182interactive shell need not exit. 1183.It Li ${parameter:+word} 1184Use Alternate Value. 1185If parameter is unset 1186or null, null is substituted; 1187otherwise, the expansion of word is 1188substituted. 1189.El 1190.Pp 1191In the parameter expansions shown previously, use of the colon in the 1192format results in a test for a parameter that is unset or null; omission 1193of the colon results in a test for a parameter that is only unset. 1194.Bl -tag -width indent 1195.It Li ${#parameter} 1196String Length. 1197The length in characters of 1198the value of parameter. 1199.El 1200.Pp 1201The following four varieties of parameter expansion provide for substring 1202processing. 1203In each case, pattern matching notation 1204(see 1205.Sx Shell Patterns ) , 1206rather than regular expression notation, 1207is used to evaluate the patterns. 1208If parameter is one of the special parameters 1209.Li * 1210or 1211.Li @ , 1212the result of the expansion is unspecified. 1213Enclosing the full parameter expansion string in double-quotes does not 1214cause the following four varieties of pattern characters to be quoted, 1215whereas quoting characters within the braces has this effect. 1216.Bl -tag -width indent 1217.It Li ${parameter%word} 1218Remove Smallest Suffix Pattern. 1219The word 1220is expanded to produce a pattern. 1221The 1222parameter expansion then results in 1223parameter, with the smallest portion of the 1224suffix matched by the pattern deleted. 1225.It Li ${parameter%%word} 1226Remove Largest Suffix Pattern. 1227The word 1228is expanded to produce a pattern. 1229The 1230parameter expansion then results in 1231parameter, with the largest portion of the 1232suffix matched by the pattern deleted. 1233.It Li ${parameter#word} 1234Remove Smallest Prefix Pattern. 1235The word 1236is expanded to produce a pattern. 1237The 1238parameter expansion then results in 1239parameter, with the smallest portion of the 1240prefix matched by the pattern deleted. 1241.It Li ${parameter##word} 1242Remove Largest Prefix Pattern. 1243The word 1244is expanded to produce a pattern. 1245The 1246parameter expansion then results in 1247parameter, with the largest portion of the 1248prefix matched by the pattern deleted. 1249.El 1250.Ss Command Substitution 1251Command substitution allows the output of a command to be substituted in 1252place of the command name itself. 1253Command substitution occurs when 1254the command is enclosed as follows: 1255.Bd -literal -offset indent 1256$(command) 1257.Ed 1258.Pp 1259or the backquoted version: 1260.Bd -literal -offset indent 1261`command` 1262.Ed 1263.Pp 1264The shell expands the command substitution by executing command in a 1265subshell environment and replacing the command substitution 1266with the standard output of the command, 1267removing sequences of one or more newlines at the end of the substitution. 1268Embedded newlines before the end of the output are not removed; 1269however, during field splitting, they may be translated into spaces 1270depending on the value of 1271.Ev IFS 1272and the quoting that is in effect. 1273.Ss Arithmetic Expansion 1274Arithmetic expansion provides a mechanism for evaluating an arithmetic 1275expression and substituting its value. 1276The format for arithmetic expansion is as follows: 1277.Bd -literal -offset indent 1278$((expression)) 1279.Ed 1280.Pp 1281The expression is treated as if it were in double-quotes, except 1282that a double-quote inside the expression is not treated specially. 1283The 1284shell expands all tokens in the expression for parameter expansion, 1285command substitution, and quote removal. 1286.Pp 1287Next, the shell treats this as an arithmetic expression and 1288substitutes the value of the expression. 1289.Ss White Space Splitting (Field Splitting) 1290After parameter expansion, command substitution, and 1291arithmetic expansion the shell scans the results of 1292expansions and substitutions that did not occur in double-quotes for 1293field splitting and multiple fields can result. 1294.Pp 1295The shell treats each character of the 1296.Ev IFS 1297as a delimiter and uses 1298the delimiters to split the results of parameter expansion and command 1299substitution into fields. 1300.Ss Pathname Expansion (File Name Generation) 1301Unless the 1302.Fl f 1303option is set, 1304file name generation is performed 1305after word splitting is complete. 1306Each word is 1307viewed as a series of patterns, separated by slashes. 1308The 1309process of expansion replaces the word with the names of 1310all existing files whose names can be formed by replacing 1311each pattern with a string that matches the specified pattern. 1312There are two restrictions on this: first, a pattern cannot match 1313a string containing a slash, and second, 1314a pattern cannot match a string starting with a period 1315unless the first character of the pattern is a period. 1316The next section describes the patterns used for both 1317Pathname Expansion and the 1318.Ic case 1319command. 1320.Ss Shell Patterns 1321A pattern consists of normal characters, which match themselves, 1322and meta-characters. 1323The meta-characters are 1324.Ql \&! , 1325.Ql * , 1326.Ql \&? , 1327and 1328.Ql \&[ . 1329These characters lose their special meanings if they are quoted. 1330When command or variable substitution is performed and the dollar sign 1331or back quotes are not double-quoted, the value of the 1332variable or the output of the command is scanned for these 1333characters and they are turned into meta-characters. 1334.Pp 1335An asterisk 1336.Pq Ql * 1337matches any string of characters. 1338A question mark 1339.Pq Ql \&? 1340matches any single character. 1341A left bracket 1342.Pq Ql \&[ 1343introduces a character class. 1344The end of the character class is indicated by a 1345.Ql \&] ; 1346if the 1347.Ql \&] 1348is missing then the 1349.Ql \&[ 1350matches a 1351.Ql \&[ 1352rather than introducing a character class. 1353A character class matches any of the characters between the square brackets. 1354A range of characters may be specified using a minus sign. 1355The character class may be complemented by making an exclamation point 1356.Pq Ql !\& 1357or the caret 1358.Pq Ql ^\& 1359the first character of the character class. 1360.Pp 1361To include a 1362.Ql \&] 1363in a character class, make it the first character listed 1364(after the 1365.Ql \&! 1366or 1367.Ql \&^ , 1368if any). 1369To include a 1370.Ql - , 1371make it the first or last character listed. 1372.Ss Built-in Commands 1373This section lists the commands which 1374are built-in because they need to perform some operation 1375that cannot be performed by a separate process. 1376In addition to 1377these, built-in versions of essential utilities 1378are provided for efficiency. 1379.Bl -tag -width indent 1380.It Ic \&: 1381A null command that returns a 0 (true) exit value. 1382.It Ic \&. Ar file 1383The commands in the specified file are read and executed by the shell. 1384The 1385.Ic return 1386command may be used to return to the 1387.Ic \&. 1388command's caller. 1389If 1390.Ar file 1391contains any 1392.Ql / 1393characters, it is used as is. 1394Otherwise, the shell searches the 1395.Ev PATH 1396for the file. 1397If it is not found in the 1398.Ev PATH , 1399it is sought in the current working directory. 1400.It Ic \&[ 1401A built-in equivalent of 1402.Xr test 1 . 1403.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc 1404If 1405.Ar name Ns = Ns Ar string 1406is specified, the shell defines the alias 1407.Ar name 1408with value 1409.Ar string . 1410If just 1411.Ar name 1412is specified, the value of the alias 1413.Ar name 1414is printed. 1415With no arguments, the 1416.Ic alias 1417built-in command prints the names and values of all defined aliases 1418(see 1419.Ic unalias ) . 1420Alias values are written with appropriate quoting so that they are 1421suitable for re-input to the shell. 1422Also see the 1423.Sx Aliases 1424subsection. 1425.It Ic bg Op Ar job ... 1426Continue the specified jobs 1427(or the current job if no jobs are given) 1428in the background. 1429.It Ic builtin Ar cmd Op Ar arg ... 1430Execute the specified built-in command, 1431.Ar cmd . 1432This is useful when the user wishes to override a shell function 1433with the same name as a built-in command. 1434.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1435List or alter key bindings for the line editor. 1436This command is documented in 1437.Xr editrc 5 . 1438.It Ic cd Oo Fl L | P Oc Op Ar directory 1439Switch to the specified 1440.Ar directory , 1441or to the directory specified in the 1442.Ev HOME 1443environment variable if no 1444.Ar directory 1445is specified. 1446If 1447.Ar directory 1448does not begin with 1449.Pa / , \&. , 1450or 1451.Pa .. , 1452then the directories listed in the 1453.Ev CDPATH 1454variable will be 1455searched for the specified 1456.Ar directory . 1457If 1458.Ev CDPATH 1459is unset, the current directory is searched. 1460The format of 1461.Ar CDPATH 1462is the same as that of 1463.Ev PATH . 1464In an interactive shell, 1465the 1466.Ic cd 1467command will print out the name of the directory 1468that it actually switched to 1469if this is different from the name that the user gave. 1470These may be different either because the 1471.Ev CDPATH 1472mechanism was used or because a symbolic link was crossed. 1473.Pp 1474If the 1475.Fl P 1476option is specified, 1477.Pa .. 1478is handled physically and symbolic links are resolved before 1479.Pa .. 1480components are processed. 1481If the 1482.Fl L 1483option is specified, 1484.Pa .. 1485is handled logically. 1486This is the default. 1487.It Ic chdir 1488A synonym for the 1489.Ic cd 1490built-in command. 1491.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 1492.It Ic command Oo Fl v | V Oc Op Ar utility 1493The first form of invocation executes the specified 1494.Ar utility 1495as a simple command (see the 1496.Sx Simple Commands 1497section). 1498.Pp 1499If the 1500.Fl p 1501option is specified, the command search is performed using a 1502default value of 1503.Ev PATH 1504that is guaranteed to find all of the standard utilities. 1505.Pp 1506If the 1507.Fl v 1508option is specified, 1509.Ar utility 1510is not executed but a description of its interpretation by the shell is 1511printed. 1512For ordinary commands the output is the path name; for shell built-in 1513commands, shell functions and keywords only the name is written. 1514Aliases are printed as 1515.Dq Ic alias Ar name Ns = Ns Ar value . 1516.Pp 1517The 1518.Fl V 1519option is identical to 1520.Fl v 1521except for the output. 1522It prints 1523.Dq Ar utility Ic is Ar description 1524where 1525.Ar description 1526is either 1527the path name to 1528.Ar utility , 1529a shell builtin, 1530a shell function, 1531a shell keyword 1532or 1533an alias for 1534.Ar value . 1535.It Ic echo Oo Fl e | n Oc Op Ar string ... 1536Print a space-separated list of the arguments to the standard output 1537and append a newline character. 1538.Bl -tag -width indent 1539.It Fl n 1540Suppress the output of the trailing newline. 1541.It Fl e 1542Process C-style backslash escape sequences. 1543.Ic echo 1544understands the following character escapes: 1545.Bl -tag -width indent 1546.It \ea 1547Alert (ring the terminal bell) 1548.It \eb 1549Backspace 1550.It \ec 1551Suppress the trailing newline (this has the side-effect of truncating the 1552line if it is not the last character) 1553.It \ee 1554The ESC character (ASCII 0x1b) 1555.It \ef 1556Formfeed 1557.It \en 1558Newline 1559.It \er 1560Carriage return 1561.It \et 1562Horizontal tab 1563.It \ev 1564Vertical tab 1565.It \e\e 1566Literal backslash 1567.It \e0nnn 1568(Zero) The character whose octal value is nnn 1569.El 1570.Pp 1571If 1572.Ar string 1573is not enclosed in quotes then the backslash itself must be escaped 1574with a backslash to protect it from the shell. 1575For example 1576.Bd -literal -offset indent 1577$ echo -e "a\evb" 1578a 1579 b 1580$ echo -e a\e\evb 1581a 1582 b 1583$ echo -e "a\e\eb" 1584a\eb 1585$ echo -e a\e\e\e\eb 1586a\eb 1587.Ed 1588.El 1589.Pp 1590Only one of the 1591.Fl e 1592and 1593.Fl n 1594options may be specified. 1595.It Ic eval Ar string ... 1596Concatenate all the arguments with spaces. 1597Then re-parse and execute the command. 1598.It Ic exec Op Ar command Op Ar arg ... 1599Unless 1600.Ar command 1601is omitted, 1602the shell process is replaced with the specified program 1603(which must be a real program, not a shell built-in command or function). 1604Any redirections on the 1605.Ic exec 1606command are marked as permanent, 1607so that they are not undone when the 1608.Ic exec 1609command finishes. 1610.It Ic exit Op Ar exitstatus 1611Terminate the shell process. 1612If 1613.Ar exitstatus 1614is given 1615it is used as the exit status of the shell; 1616otherwise the exit status of the preceding command is used. 1617.It Ic export Ar name ... 1618.It Ic export Op Fl p 1619The specified names are exported so that they will 1620appear in the environment of subsequent commands. 1621The only way to un-export a variable is to 1622.Ic unset 1623it. 1624The shell allows the value of a variable to be set 1625at the same time as it is exported by writing 1626.Bd -literal -offset indent 1627export name=value 1628.Ed 1629.Pp 1630With no arguments the export command lists the names 1631of all exported variables. 1632If the 1633.Fl p 1634option is specified, the exported variables are printed as 1635.Dq Ic export Ar name Ns = Ns Ar value 1636lines, suitable for re-input to the shell. 1637.It Ic false 1638A null command that returns a non-zero (false) exit value. 1639.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 1640.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 1641.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 1642The 1643.Ic fc 1644built-in command lists, or edits and re-executes, 1645commands previously entered to an interactive shell. 1646.Bl -tag -width indent 1647.It Fl e Ar editor 1648Use the editor named by 1649.Ar editor 1650to edit the commands. 1651The editor string is a command name, 1652subject to search via the 1653.Ev PATH 1654variable. 1655The value in the 1656.Ev FCEDIT 1657variable is used as a default when 1658.Fl e 1659is not specified. 1660If 1661.Ev FCEDIT 1662is null or unset, the value of the 1663.Ev EDITOR 1664variable is used. 1665If 1666.Ev EDITOR 1667is null or unset, 1668.Xr ed 1 1669is used as the editor. 1670.It Fl l No (ell) 1671List the commands rather than invoking 1672an editor on them. 1673The commands are written in the 1674sequence indicated by the first and last operands, as 1675affected by 1676.Fl r , 1677with each command preceded by the command number. 1678.It Fl n 1679Suppress command numbers when listing with 1680.Fl l . 1681.It Fl r 1682Reverse the order of the commands listed 1683(with 1684.Fl l ) 1685or edited 1686(with neither 1687.Fl l 1688nor 1689.Fl s ) . 1690.It Fl s 1691Re-execute the command without invoking an editor. 1692.It Ar first 1693.It Ar last 1694Select the commands to list or edit. 1695The number of previous commands that can be accessed 1696are determined by the value of the 1697.Ev HISTSIZE 1698variable. 1699The value of 1700.Ar first 1701or 1702.Ar last 1703or both are one of the following: 1704.Bl -tag -width indent 1705.It Ar [+]num 1706A positive number representing a command number; 1707command numbers can be displayed with the 1708.Fl l 1709option. 1710.It Ar -num 1711A negative decimal number representing the 1712command that was executed 1713.Ar num 1714of 1715commands previously. 1716For example, -1 is the immediately previous command. 1717.It Ar string 1718A string indicating the most recently entered command 1719that begins with that string. 1720If the 1721.Ar old=new 1722operand is not also specified with 1723.Fl s , 1724the string form of the first operand cannot contain an embedded equal sign. 1725.El 1726.El 1727.Pp 1728The following environment variables affect the execution of 1729.Ic fc : 1730.Bl -tag -width ".Ev HISTSIZE" 1731.It Ev FCEDIT 1732Name of the editor to use for history editing. 1733.It Ev HISTSIZE 1734The number of previous commands that are accessible. 1735.El 1736.It Ic fg Op Ar job 1737Move the specified 1738.Ar job 1739or the current job to the foreground. 1740.It Ic getopts Ar optstring Ar var 1741The POSIX 1742.Ic getopts 1743command. 1744The 1745.Ic getopts 1746command deprecates the older 1747.Xr getopt 1 1748command. 1749The first argument should be a series of letters, each possibly 1750followed by a colon which indicates that the option takes an argument. 1751The specified variable is set to the parsed option. 1752The index of 1753the next argument is placed into the shell variable 1754.Ev OPTIND . 1755If an option takes an argument, it is placed into the shell variable 1756.Ev OPTARG . 1757If an invalid option is encountered, 1758.Ev var 1759is set to 1760.Ql \&? . 1761It returns a false value (1) when it encounters the end of the options. 1762.It Ic hash Oo Fl rv Oc Op Ar command ... 1763The shell maintains a hash table which remembers the locations of commands. 1764With no arguments whatsoever, the 1765.Ic hash 1766command prints out the contents of this table. 1767Entries which have not been looked at since the last 1768.Ic cd 1769command are marked with an asterisk; 1770it is possible for these entries to be invalid. 1771.Pp 1772With arguments, the 1773.Ic hash 1774command removes each specified 1775.Ar command 1776from the hash table (unless they are functions) and then locates it. 1777With the 1778.Fl v 1779option, 1780.Ic hash 1781prints the locations of the commands as it finds them. 1782The 1783.Fl r 1784option causes the 1785.Ic hash 1786command to delete all the entries in the hash table except for functions. 1787.It Ic jobid Op Ar job 1788Print the process id's of the processes in the specified 1789.Ar job . 1790If the 1791.Ar job 1792argument is omitted, use the current job. 1793.It Ic jobs Oo Fl lps Oc Op Ar job ... 1794Print information about the specified jobs, or all jobs if no 1795.Ar job 1796argument is given. 1797The information printed includes job ID, status and command name. 1798.Pp 1799If the 1800.Fl l 1801option is specified, the PID of each job is also printed. 1802If the 1803.Fl p 1804option is specified, only the process IDs for the process group leaders 1805are printed, one per line. 1806If the 1807.Fl s 1808option is specified, only the PIDs of the job commands are printed, one per 1809line. 1810.It Ic local Oo Ar variable ... Oc Op Fl 1811See the 1812.Sx Functions 1813subsection. 1814.It Ic pwd Op Fl L | P 1815Print the path of the current directory. 1816The built-in command may 1817differ from the program of the same name because the 1818built-in command remembers what the current directory 1819is rather than recomputing it each time. 1820This makes 1821it faster. 1822However, if the current directory is 1823renamed, 1824the built-in version of 1825.Xr pwd 1 1826will continue to print the old name for the directory. 1827.Pp 1828If the 1829.Fl P 1830option is specified, symbolic links are resolved. 1831If the 1832.Fl L 1833option is specified, the shell's notion of the current directory 1834is printed (symbolic links are not resolved). 1835This is the default. 1836.It Ic read Oo Fl p Ar prompt Oc Oo Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 1837The 1838.Ar prompt 1839is printed if the 1840.Fl p 1841option is specified 1842and the standard input is a terminal. 1843Then a line is 1844read from the standard input. 1845The trailing newline 1846is deleted from the line and the line is split as 1847described in the section on 1848.Sx White Space Splitting (Field Splitting) 1849above, and 1850the pieces are assigned to the variables in order. 1851If there are more pieces than variables, the remaining 1852pieces (along with the characters in 1853.Ev IFS 1854that separated them) 1855are assigned to the last variable. 1856If there are more variables than pieces, the remaining 1857variables are assigned the null string. 1858.Pp 1859Backslashes are treated specially, unless the 1860.Fl r 1861option is 1862specified. 1863If a backslash is followed by 1864a newline, the backslash and the newline will be 1865deleted. 1866If a backslash is followed by any other 1867character, the backslash will be deleted and the following 1868character will be treated as though it were not in 1869.Ev IFS , 1870even if it is. 1871.Pp 1872If the 1873.Fl t 1874option is specified and the 1875.Ar timeout 1876elapses before any input is supplied, 1877the 1878.Ic read 1879command will return an exit status of 1 without assigning any values. 1880The 1881.Ar timeout 1882value may optionally be followed by one of 1883.Ql s , 1884.Ql m 1885or 1886.Ql h 1887to explicitly specify seconds, minutes or hours. 1888If none is supplied, 1889.Ql s 1890is assumed. 1891.Pp 1892The 1893.Fl e 1894option exists only for backward compatibility with older scripts. 1895.It Ic readonly Oo Fl p Oc Op Ar name ... 1896Each specified 1897.Ar name 1898is marked as read only, 1899so that it cannot be subsequently modified or unset. 1900The shell allows the value of a variable to be set 1901at the same time as it is marked read only 1902by using the following form: 1903.Bd -literal -offset indent 1904readonly name=value 1905.Ed 1906.Pp 1907With no arguments the 1908.Ic readonly 1909command lists the names of all read only variables. 1910If the 1911.Fl p 1912option is specified, the read-only variables are printed as 1913.Dq Ic readonly Ar name Ns = Ns Ar value 1914lines, suitable for re-input to the shell. 1915.It Ic return Op Ar exitstatus 1916See the 1917.Sx Functions 1918subsection. 1919.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 1920.Fl c Ar string Oc Op Fl - Ar arg ... 1921The 1922.Ic set 1923command performs three different functions: 1924.Bl -item 1925.It 1926With no arguments, it lists the values of all shell variables. 1927.It 1928If options are given, 1929either in short form or using the long 1930.Dq Fl /+o Ar longname 1931form, 1932it sets or clears the specified options as described in the section called 1933.Sx Argument List Processing . 1934.It 1935If the 1936.Dq Fl - 1937option is specified, 1938.Ic set 1939will replace the shell's positional parameters with the subsequent 1940arguments. 1941If no arguments follow the 1942.Dq Fl - 1943option, 1944all the positional parameters will be cleared, 1945which is equivalent to executing the command 1946.Dq Li shift $# . 1947The 1948.Dq Fl - 1949flag may be omitted when specifying arguments to be used 1950as positional replacement parameters. 1951This is not recommended, 1952because the first argument may begin with a dash 1953.Pq Ql - 1954or a plus 1955.Pq Ql + , 1956which the 1957.Ic set 1958command will interpret as a request to enable or disable options. 1959.El 1960.It Ic setvar Ar variable Ar value 1961Assigns the specified 1962.Ar value 1963to the specified 1964.Ar variable . 1965.Ic Setvar 1966is intended to be used in functions that 1967assign values to variables whose names are passed as parameters. 1968In general it is better to write 1969.Bd -literal -offset indent 1970variable=value 1971.Ed 1972rather than using 1973.Ic setvar . 1974.It Ic shift Op Ar n 1975Shift the positional parameters 1976.Ar n 1977times, or once if 1978.Ar n 1979is not specified. 1980A shift sets the value of $1 to the value of $2, 1981the value of $2 to the value of $3, and so on, 1982decreasing the value of $# by one. 1983If there are zero positional parameters, shifting does not do anything. 1984.It Ic test 1985A built-in equivalent of 1986.Xr test 1 . 1987.It Ic times 1988Print the amount of time spent executing the shell and its children. 1989The first output line shows the user and system times for the shell 1990itself, the second one contains the user and system times for the 1991children. 1992.It Ic trap Oo Ar action Oc Ar signal ... 1993.It Ic trap Fl l 1994Cause the shell to parse and execute 1995.Ar action 1996when any specified 1997.Ar signal 1998is received. 1999The signals are specified by name or number. 2000In addition, the pseudo-signal 2001.Cm EXIT 2002may be used to specify an action that is performed when the shell terminates. 2003The 2004.Ar action 2005may be an empty string or a dash 2006.Pq Ql - ; 2007the former causes the specified signal to be ignored 2008and the latter causes the default action to be taken. 2009Omitting the 2010.Ar action 2011is another way to request the default action, for compatibility reasons this 2012usage is not recommended though. 2013When the shell forks off a subshell, 2014it resets trapped (but not ignored) signals to the default action. 2015The 2016.Ic trap 2017command has no effect on signals that were ignored on entry to the shell. 2018.Pp 2019Option 2020.Fl l 2021causes the 2022.Ic trap 2023command to display a list of valid signal names. 2024.It Ic true 2025A null command that returns a 0 (true) exit value. 2026.It Ic type Op Ar name ... 2027Interpret each 2028.Ar name 2029as a command and print the resolution of the command search. 2030Possible resolutions are: 2031shell keyword, alias, shell built-in command, command, tracked alias 2032and not found. 2033For aliases the alias expansion is printed; 2034for commands and tracked aliases 2035the complete pathname of the command is printed. 2036.It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit 2037Set or display resource limits (see 2038.Xr getrlimit 2 ) . 2039If 2040.Ar limit 2041is specified, the named resource will be set; 2042otherwise the current resource value will be displayed. 2043.Pp 2044If 2045.Fl H 2046is specified, the hard limits will be set or displayed. 2047While everybody is allowed to reduce a hard limit, 2048only the superuser can increase it. 2049The 2050.Fl S 2051option 2052specifies the soft limits instead. 2053When displaying limits, 2054only one of 2055.Fl S 2056or 2057.Fl H 2058can be given. 2059The default is to display the soft limits, 2060and to set both the hard and the soft limits. 2061.Pp 2062Option 2063.Fl a 2064causes the 2065.Ic ulimit 2066command to display all resources. 2067The parameter 2068.Ar limit 2069is not acceptable in this mode. 2070.Pp 2071The remaining options specify which resource value is to be 2072displayed or modified. 2073They are mutually exclusive. 2074.Bl -tag -width indent 2075.It Fl b Ar sbsize 2076The maximum size of socket buffer usage, in bytes. 2077.It Fl c Ar coredumpsize 2078The maximal size of core dump files, in 512-byte blocks. 2079.It Fl d Ar datasize 2080The maximal size of the data segment of a process, in kilobytes. 2081.It Fl f Ar filesize 2082The maximal size of a file, in 512-byte blocks. 2083.It Fl l Ar lockedmem 2084The maximal size of memory that can be locked by a process, in 2085kilobytes. 2086.It Fl m Ar memoryuse 2087The maximal resident set size of a process, in kilobytes. 2088.It Fl n Ar nofiles 2089The maximal number of descriptors that could be opened by a process. 2090.It Fl s Ar stacksize 2091The maximal size of the stack segment, in kilobytes. 2092.It Fl t Ar time 2093The maximal amount of CPU time to be used by each process, in seconds. 2094.It Fl u Ar userproc 2095The maximal number of simultaneous processes for this user ID. 2096.It Fl v Ar virtualmem 2097The maximal virtual size of a process, in kilobytes. 2098.El 2099.It Ic umask Oo Fl S Oc Op Ar mask 2100Set the file creation mask (see 2101.Xr umask 2 ) 2102to the octal or symbolic (see 2103.Xr chmod 1 ) 2104value specified by 2105.Ar mask . 2106If the argument is omitted, the current mask value is printed. 2107If the 2108.Fl S 2109option is specified, the output is symbolic, otherwise the output is octal. 2110.It Ic unalias Oo Fl a Oc Op Ar name ... 2111The specified alias names are removed. 2112If 2113.Fl a 2114is specified, all aliases are removed. 2115.It Ic unset Oo Fl fv Oc Ar name ... 2116The specified variables or functions are unset and unexported. 2117If the 2118.Fl v 2119option is specified or no options are given, the 2120.Ar name 2121arguments are treated as variable names. 2122If the 2123.Fl f 2124option is specified, the 2125.Ar name 2126arguments are treated as function names. 2127.It Ic wait Op Ar job 2128Wait for the specified 2129.Ar job 2130to complete and return the exit status of the last process in the 2131.Ar job . 2132If the argument is omitted, wait for all jobs to complete 2133and return an exit status of zero. 2134.El 2135.Ss Commandline Editing 2136When 2137.Nm 2138is being used interactively from a terminal, the current command 2139and the command history 2140(see 2141.Ic fc 2142in 2143.Sx Built-in Commands ) 2144can be edited using vi-mode command line editing. 2145This mode uses commands similar 2146to a subset of those described in the vi man page. 2147The command 2148.Dq Li set -o vi 2149(or 2150.Dq Li set -V ) 2151enables vi-mode editing and places 2152.Nm 2153into vi insert mode. 2154With vi-mode enabled, 2155.Nm 2156can be switched between insert mode and command mode by typing 2157.Aq ESC . 2158Hitting 2159.Aq return 2160while in command mode will pass the line to the shell. 2161.Pp 2162Similarly, the 2163.Dq Li set -o emacs 2164(or 2165.Dq Li set -E ) 2166command can be used to enable a subset of 2167emacs-style command line editing features. 2168.Sh ENVIRONMENT 2169The following environment variables affect the execution of 2170.Nm : 2171.Bl -tag -width ".Ev HISTSIZE" 2172.It Ev CDPATH 2173The search path used with the 2174.Ic cd 2175built-in. 2176.It Ev EDITOR 2177The fallback editor used with the 2178.Ic fc 2179built-in. 2180If not set, the default editor is 2181.Xr ed 1 . 2182.It Ev FCEDIT 2183The default editor used with the 2184.Ic fc 2185built-in. 2186.It Ev HISTSIZE 2187The number of previous commands that are accessible. 2188.It Ev HOME 2189The starting directory of 2190.Nm . 2191.It Ev IFS 2192Input Field Separators. 2193This is normally set to 2194.Aq space , 2195.Aq tab , 2196and 2197.Aq newline . 2198See the 2199.Sx White Space Splitting 2200section for more details. 2201.It Ev MAIL 2202The name of a mail file, that will be checked for the arrival of new 2203mail. 2204Overridden by 2205.Ev MAILPATH . 2206.It Ev MAILPATH 2207A colon 2208.Pq Ql \&: 2209separated list of file names, for the shell to check for incoming 2210mail. 2211This environment setting overrides the 2212.Ev MAIL 2213setting. 2214There is a maximum of 10 mailboxes that can be monitored at once. 2215.It Ev PATH 2216The default search path for executables. 2217See the 2218.Sx Path Search 2219section for details. 2220.It Ev PS1 2221The primary prompt string, which defaults to 2222.Dq Li "$ " , 2223unless you are the superuser, in which case it defaults to 2224.Dq Li "# " . 2225.It Ev PS2 2226The secondary prompt string, which defaults to 2227.Dq Li "> " . 2228.It Ev PS4 2229The prefix for the trace output (if 2230.Fl x 2231is active). 2232The default is 2233.Dq Li "+ " . 2234.It Ev TERM 2235The default terminal setting for the shell. 2236This is inherited by children of the shell, and is used in the history 2237editing modes. 2238.El 2239.Sh EXIT STATUS 2240Errors that are detected by the shell, such as a syntax error, will 2241cause the shell to exit with a non-zero exit status. 2242If the shell is not an interactive shell, the execution of the shell 2243file will be aborted. 2244Otherwise the shell will return the exit status of the last command 2245executed, or if the exit builtin is used with a numeric argument, it 2246will return the argument. 2247.Sh SEE ALSO 2248.Xr builtin 1 , 2249.Xr chsh 1 , 2250.Xr echo 1 , 2251.Xr ed 1 , 2252.Xr emacs 1 Pq Pa pkgsrc/editors/emacs , 2253.Xr expr 1 , 2254.Xr getopt 1 , 2255.Xr printf 1 , 2256.Xr pwd 1 , 2257.Xr test 1 , 2258.Xr vi 1 , 2259.Xr execve 2 , 2260.Xr getrlimit 2 , 2261.Xr umask 2 , 2262.Xr editrc 5 , 2263.Xr script 7 2264.Sh HISTORY 2265A 2266.Nm 2267command, the Thompson shell, appeared in 2268.At v1 . 2269It was superseded in 2270.At v7 2271by the Bourne shell, which inherited the name 2272.Nm . 2273.Pp 2274This version of 2275.Nm 2276was rewritten in 1989 under the 2277.Bx 2278license after the Bourne shell from 2279.At V.4 . 2280.Sh AUTHORS 2281This version of 2282.Nm 2283was originally written by 2284.An Kenneth Almquist . 2285.Sh BUGS 2286The 2287.Nm 2288utility does not recognize multibyte characters. 2289.Pp 2290The characters generated by filename completion should probably be quoted 2291to ensure that the filename is still valid after the input line has been 2292processed. 2293