1.\"- 2.\" Copyright (c) 1991, 1993 3.\" The Regents of the University of California. All rights reserved. 4.\" 5.\" This code is derived from software contributed to Berkeley by 6.\" Kenneth Almquist. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 33.\" $FreeBSD$ 34.\" 35.Dd June 14, 2013 36.Dt SH 1 37.Os 38.Sh NAME 39.Nm sh 40.Nd command interpreter (shell) 41.Sh SYNOPSIS 42.Nm 43.Op Fl /+abCEefIimnPpTuVvx 44.Op Fl /+o Ar longname 45.Oo 46.Ar script 47.Op Ar arg ... 48.Oc 49.Nm 50.Op Fl /+abCEefIimnPpTuVvx 51.Op Fl /+o Ar longname 52.Fl c Ar string 53.Oo 54.Ar name 55.Op Ar arg ... 56.Oc 57.Nm 58.Op Fl /+abCEefIimnPpTuVvx 59.Op Fl /+o Ar longname 60.Fl s 61.Op Ar arg ... 62.Sh DESCRIPTION 63The 64.Nm 65utility is the standard command interpreter for the system. 66The current version of 67.Nm 68is close to the 69.St -p1003.1 70specification for the shell. 71It only supports features 72designated by 73.Tn POSIX , 74plus a few Berkeley extensions. 75This man page is not intended to be a tutorial nor a complete 76specification of the shell. 77.Ss Overview 78The shell is a command that reads lines from 79either a file or the terminal, interprets them, and 80generally executes other commands. 81It is the program that is started when a user logs into the system, 82although a user can select a different shell with the 83.Xr chsh 1 84command. 85The shell 86implements a language that has flow control constructs, 87a macro facility that provides a variety of features in 88addition to data storage, along with built-in history and line 89editing capabilities. 90It incorporates many features to 91aid interactive use and has the advantage that the interpretative 92language is common to both interactive and non-interactive 93use (shell scripts). 94That is, commands can be typed directly 95to the running shell or can be put into a file, 96which can be executed directly by the shell. 97.Ss Invocation 98.\" 99.\" XXX This next sentence is incredibly confusing. 100.\" 101If no arguments are present and if the standard input of the shell 102is connected to a terminal 103(or if the 104.Fl i 105option is set), 106the shell is considered an interactive shell. 107An interactive shell 108generally prompts before each command and handles programming 109and command errors differently (as described below). 110When first starting, the shell inspects argument 0, and 111if it begins with a dash 112.Pq Ql - , 113the shell is also considered a login shell. 114This is normally done automatically by the system 115when the user first logs in. 116A login shell first reads commands 117from the files 118.Pa /etc/profile 119and then 120.Pa .profile 121in a user's home directory, 122if they exist. 123If the environment variable 124.Ev ENV 125is set on entry to a shell, or is set in the 126.Pa .profile 127of a login shell, the shell then subjects its value to parameter expansion 128and arithmetic expansion and reads commands from the named file. 129Therefore, a user should place commands that are to be executed only 130at login time in the 131.Pa .profile 132file, and commands that are executed for every shell inside the 133.Ev ENV 134file. 135The user can set the 136.Ev ENV 137variable to some file by placing the following line in the file 138.Pa .profile 139in the home directory, 140substituting for 141.Pa .shrc 142the filename desired: 143.Pp 144.Dl "ENV=$HOME/.shrc; export ENV" 145.Pp 146The first non-option argument specified on the command line 147will be treated as the 148name of a file from which to read commands (a shell script), and 149the remaining arguments are set as the positional parameters 150of the shell 151.Li ( $1 , $2 , 152etc.). 153Otherwise, the shell reads commands 154from its standard input. 155.Pp 156Unlike older versions of 157.Nm 158the 159.Ev ENV 160script is only sourced on invocation of interactive shells. 161This 162closes a well-known, and sometimes easily exploitable security 163hole related to poorly thought out 164.Ev ENV 165scripts. 166.Ss Argument List Processing 167All of the single letter options to 168.Nm 169have a corresponding long name, 170with the exception of 171.Fl c 172and 173.Fl /+o . 174These long names are provided next to the single letter options 175in the descriptions below. 176The long name for an option may be specified as an argument to the 177.Fl /+o 178option of 179.Nm . 180Once the shell is running, 181the long name for an option may be specified as an argument to the 182.Fl /+o 183option of the 184.Ic set 185built-in command 186(described later in the section called 187.Sx Built-in Commands ) . 188Introducing an option with a dash 189.Pq Ql - 190enables the option, 191while using a plus 192.Pq Ql + 193disables the option. 194A 195.Dq Li -- 196or plain 197.Ql - 198will stop option processing and will force the remaining 199words on the command line to be treated as arguments. 200The 201.Fl /+o 202and 203.Fl c 204options do not have long names. 205They take arguments and are described after the single letter options. 206.Bl -tag -width indent 207.It Fl a Li allexport 208Flag variables for export when assignments are made to them. 209.It Fl b Li notify 210Enable asynchronous notification of background job 211completion. 212(UNIMPLEMENTED) 213.It Fl C Li noclobber 214Do not overwrite existing files with 215.Ql > . 216.It Fl E Li emacs 217Enable the built-in 218.Xr emacs 1 219command line editor (disables the 220.Fl V 221option if it has been set; 222set automatically when interactive on terminals). 223.It Fl e Li errexit 224Exit immediately if any untested command fails in non-interactive mode. 225The exit status of a command is considered to be 226explicitly tested if the command is part of the list used to control 227an 228.Ic if , elif , while , 229or 230.Ic until ; 231if the command is the left 232hand operand of an 233.Dq Li && 234or 235.Dq Li || 236operator; or if the command is a pipeline preceded by the 237.Ic !\& 238operator. 239If a shell function is executed and its exit status is explicitly 240tested, all commands of the function are considered to be tested as 241well. 242.It Fl f Li noglob 243Disable pathname expansion. 244.It Fl h Li trackall 245A do-nothing option for 246.Tn POSIX 247compliance. 248.It Fl I Li ignoreeof 249Ignore 250.Dv EOF Ap s 251from input when in interactive mode. 252.It Fl i Li interactive 253Force the shell to behave interactively. 254.It Fl m Li monitor 255Turn on job control (set automatically when interactive). 256.It Fl n Li noexec 257If not interactive, read commands but do not 258execute them. 259This is useful for checking the 260syntax of shell scripts. 261.It Fl P Li physical 262Change the default for the 263.Ic cd 264and 265.Ic pwd 266commands from 267.Fl L 268(logical directory layout) 269to 270.Fl P 271(physical directory layout). 272.It Fl p Li privileged 273Turn on privileged mode. 274This mode is enabled on startup 275if either the effective user or group ID is not equal to the 276real user or group ID. 277Turning this mode off sets the 278effective user and group IDs to the real user and group IDs. 279When this mode is enabled for interactive shells, the file 280.Pa /etc/suid_profile 281is sourced instead of 282.Pa ~/.profile 283after 284.Pa /etc/profile 285is sourced, and the contents of the 286.Ev ENV 287variable are ignored. 288.It Fl s Li stdin 289Read commands from standard input (set automatically 290if no file arguments are present). 291This option has 292no effect when set after the shell has already started 293running (i.e., when set with the 294.Ic set 295command). 296.It Fl T Li trapsasync 297When waiting for a child, execute traps immediately. 298If this option is not set, 299traps are executed after the child exits, 300as specified in 301.St -p1003.2 . 302This nonstandard option is useful for putting guarding shells around 303children that block signals. 304The surrounding shell may kill the child 305or it may just return control to the tty and leave the child alone, 306like this: 307.Bd -literal -offset indent 308sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 309.Ed 310.It Fl u Li nounset 311Write a message to standard error when attempting 312to expand a variable, a positional parameter or 313the special parameter 314.Va \&! 315that is not set, and if the 316shell is not interactive, exit immediately. 317.It Fl V Li vi 318Enable the built-in 319.Xr vi 1 320command line editor (disables 321.Fl E 322if it has been set). 323.It Fl v Li verbose 324The shell writes its input to standard error 325as it is read. 326Useful for debugging. 327.It Fl x Li xtrace 328Write each command 329(preceded by the value of the 330.Va PS4 331variable subjected to parameter expansion and arithmetic expansion) 332to standard error before it is executed. 333Useful for debugging. 334.El 335.Pp 336The 337.Fl c 338option causes the commands to be read from the 339.Ar string 340operand instead of from the standard input. 341Keep in mind that this option only accepts a single string as its 342argument, hence multi-word strings must be quoted. 343.Pp 344The 345.Fl /+o 346option takes as its only argument the long name of an option 347to be enabled or disabled. 348For example, the following two invocations of 349.Nm 350both enable the built-in 351.Xr emacs 1 352command line editor: 353.Bd -literal -offset indent 354set -E 355set -o emacs 356.Ed 357.Pp 358If used without an argument, the 359.Fl o 360option displays the current option settings in a human-readable format. 361If 362.Cm +o 363is used without an argument, the current option settings are output 364in a format suitable for re-input into the shell. 365.Ss Lexical Structure 366The shell reads input in terms of lines from a file and breaks 367it up into words at whitespace (blanks and tabs), and at 368certain sequences of 369characters called 370.Dq operators , 371which are special to the shell. 372There are two types of operators: control operators and 373redirection operators (their meaning is discussed later). 374The following is a list of valid operators: 375.Bl -tag -width indent 376.It Control operators: 377.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 378.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en 379.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li || 380.El 381.It Redirection operators: 382.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 383.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 384.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \& 385.El 386.El 387.Pp 388The character 389.Ql # 390introduces a comment if used at the beginning of a word. 391The word starting with 392.Ql # 393and the rest of the line are ignored. 394.Pp 395.Tn ASCII 396.Dv NUL 397characters (character code 0) are not allowed in shell input. 398.Ss Quoting 399Quoting is used to remove the special meaning of certain characters 400or words to the shell, such as operators, whitespace, keywords, 401or alias names. 402.Pp 403There are four types of quoting: matched single quotes, 404dollar-single quotes, 405matched double quotes, and backslash. 406.Bl -tag -width indent 407.It Single Quotes 408Enclosing characters in single quotes preserves the literal 409meaning of all the characters (except single quotes, making 410it impossible to put single-quotes in a single-quoted string). 411.It Dollar-Single Quotes 412Enclosing characters between 413.Li $' 414and 415.Li ' 416preserves the literal meaning of all characters 417except backslashes and single quotes. 418A backslash introduces a C-style escape sequence: 419.Bl -tag -width xUnnnnnnnn 420.It \ea 421Alert (ring the terminal bell) 422.It \eb 423Backspace 424.It \ec Ns Ar c 425The control character denoted by 426.Li ^ Ns Ar c 427in 428.Xr stty 1 . 429If 430.Ar c 431is a backslash, it must be doubled. 432.It \ee 433The ESC character 434.Tn ( ASCII 4350x1b) 436.It \ef 437Formfeed 438.It \en 439Newline 440.It \er 441Carriage return 442.It \et 443Horizontal tab 444.It \ev 445Vertical tab 446.It \e\e 447Literal backslash 448.It \e\&' 449Literal single-quote 450.It \e\&" 451Literal double-quote 452.It \e Ns Ar nnn 453The byte whose octal value is 454.Ar nnn 455(one to three digits) 456.It \ex Ns Ar nn 457The byte whose hexadecimal value is 458.Ar nn 459(one or more digits only the last two of which are used) 460.It \eu Ns Ar nnnn 461The Unicode code point 462.Ar nnnn 463(four hexadecimal digits) 464.It \eU Ns Ar nnnnnnnn 465The Unicode code point 466.Ar nnnnnnnn 467(eight hexadecimal digits) 468.El 469.Pp 470The sequences for Unicode code points are currently only useful with 471UTF-8 locales. 472They reject code point 0 and UTF-16 surrogates. 473.Pp 474If an escape sequence would produce a byte with value 0, 475that byte and the rest of the string until the matching single-quote 476are ignored. 477.Pp 478Any other string starting with a backslash is an error. 479.It Double Quotes 480Enclosing characters within double quotes preserves the literal 481meaning of all characters except dollar sign 482.Pq Ql $ , 483backquote 484.Pq Ql ` , 485and backslash 486.Pq Ql \e . 487The backslash inside double quotes is historically weird. 488It remains literal unless it precedes the following characters, 489which it serves to quote: 490.Pp 491.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 492.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en 493.El 494.It Backslash 495A backslash preserves the literal meaning of the following 496character, with the exception of the newline character 497.Pq Ql \en . 498A backslash preceding a newline is treated as a line continuation. 499.El 500.Ss Keywords 501Keywords or reserved words are words that have special meaning to the 502shell and are recognized at the beginning of a line and 503after a control operator. 504The following are keywords: 505.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 506.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 507.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 508.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 509.El 510.Ss Aliases 511An alias is a name and corresponding value set using the 512.Ic alias 513built-in command. 514Wherever the command word of a simple command may occur, 515and after checking for keywords if a keyword may occur, the shell 516checks the word to see if it matches an alias. 517If it does, it replaces it in the input stream with its value. 518For example, if there is an alias called 519.Dq Li lf 520with the value 521.Dq Li "ls -F" , 522then the input 523.Pp 524.Dl "lf foobar" 525.Pp 526would become 527.Pp 528.Dl "ls -F foobar" 529.Pp 530Aliases provide a convenient way for naive users to 531create shorthands for commands without having to learn how 532to create functions with arguments. 533Using aliases in scripts is discouraged 534because the command that defines them must be executed 535before the code that uses them is parsed. 536This is fragile and not portable. 537.Pp 538An alias name may be escaped in a command line, so that it is not 539replaced by its alias value, by using quoting characters within or 540adjacent to the alias name. 541This is most often done by prefixing 542an alias name with a backslash to execute a function, built-in, or 543normal program with the same name. 544See the 545.Sx Quoting 546subsection. 547.Ss Commands 548The shell interprets the words it reads according to a 549language, the specification of which is outside the scope 550of this man page (refer to the BNF in the 551.St -p1003.2 552document). 553Essentially though, a line is read and if 554the first word of the line (or after a control operator) 555is not a keyword, then the shell has recognized a 556simple command. 557Otherwise, a complex command or some 558other special construct may have been recognized. 559.Ss Simple Commands 560If a simple command has been recognized, the shell performs 561the following actions: 562.Bl -enum 563.It 564Leading words of the form 565.Dq Li name=value 566are stripped off and assigned to the environment of 567the simple command. 568Redirection operators and 569their arguments (as described below) are stripped 570off and saved for processing. 571.It 572The remaining words are expanded as described in 573the section called 574.Sx Word Expansions , 575and the first remaining word is considered the command 576name and the command is located. 577The remaining 578words are considered the arguments of the command. 579If no command name resulted, then the 580.Dq Li name=value 581variable assignments recognized in 1) affect the 582current shell. 583.It 584Redirections are performed as described in 585the next section. 586.El 587.Ss Redirections 588Redirections are used to change where a command reads its input 589or sends its output. 590In general, redirections open, close, or 591duplicate an existing reference to a file. 592The overall format 593used for redirection is: 594.Pp 595.D1 Oo Ar n Oc Ar redir-op file 596.Pp 597The 598.Ar redir-op 599is one of the redirection operators mentioned 600previously. 601The following gives some examples of how these 602operators can be used. 603Note that stdin and stdout are commonly used abbreviations 604for standard input and standard output respectively. 605.Bl -tag -width "1234567890XX" -offset indent 606.It Oo Ar n Oc Ns Li > Ar file 607redirect stdout (or file descriptor 608.Ar n ) 609to 610.Ar file 611.It Oo Ar n Oc Ns Li >| Ar file 612same as above, but override the 613.Fl C 614option 615.It Oo Ar n Oc Ns Li >> Ar file 616append stdout (or file descriptor 617.Ar n ) 618to 619.Ar file 620.It Oo Ar n Oc Ns Li < Ar file 621redirect stdin (or file descriptor 622.Ar n ) 623from 624.Ar file 625.It Oo Ar n Oc Ns Li <> Ar file 626redirect stdin (or file descriptor 627.Ar n ) 628to and from 629.Ar file 630.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 631duplicate stdin (or file descriptor 632.Ar n1 ) 633from file descriptor 634.Ar n2 635.It Oo Ar n Oc Ns Li <&- 636close stdin (or file descriptor 637.Ar n ) 638.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 639duplicate stdout (or file descriptor 640.Ar n1 ) 641to file descriptor 642.Ar n2 643.It Oo Ar n Oc Ns Li >&- 644close stdout (or file descriptor 645.Ar n ) 646.El 647.Pp 648The following redirection is often called a 649.Dq here-document . 650.Bd -unfilled -offset indent 651.Oo Ar n Oc Ns Li << Ar delimiter 652.Ar here-doc-text 653.Ar ... 654.Ar delimiter 655.Ed 656.Pp 657All the text on successive lines up to the delimiter is 658saved away and made available to the command on standard 659input, or file descriptor 660.Ar n 661if it is specified. 662If the 663.Ar delimiter 664as specified on the initial line is quoted, then the 665.Ar here-doc-text 666is treated literally, otherwise the text is subjected to 667parameter expansion, command substitution, and arithmetic 668expansion (as described in the section on 669.Sx Word Expansions ) . 670If the operator is 671.Dq Li <<- 672instead of 673.Dq Li << , 674then leading tabs 675in the 676.Ar here-doc-text 677are stripped. 678.Ss Search and Execution 679There are three types of commands: shell functions, 680built-in commands, and normal programs. 681The command is searched for (by name) in that order. 682The three types of commands are all executed in a different way. 683.Pp 684When a shell function is executed, all of the shell positional 685parameters (except 686.Li $0 , 687which remains unchanged) are 688set to the arguments of the shell function. 689The variables which are explicitly placed in the environment of 690the command (by placing assignments to them before the 691function name) are made local to the function and are set 692to the values given. 693Then the command given in the function definition is executed. 694The positional parameters are restored to their original values 695when the command completes. 696This all occurs within the current shell. 697.Pp 698Shell built-in commands are executed internally to the shell, without 699spawning a new process. 700There are two kinds of built-in commands: regular and special. 701Assignments before special builtins persist after they finish 702executing and assignment errors, redirection errors and certain 703operand errors cause a script to be aborted. 704Special builtins cannot be overridden with a function. 705Both regular and special builtins can affect the shell in ways 706normal programs cannot. 707.Pp 708Otherwise, if the command name does not match a function 709or built-in command, the command is searched for as a normal 710program in the file system (as described in the next section). 711When a normal program is executed, the shell runs the program, 712passing the arguments and the environment to the program. 713If the program is not a normal executable file 714(i.e., if it does not begin with the 715.Dq "magic number" 716whose 717.Tn ASCII 718representation is 719.Dq Li #! , 720resulting in an 721.Er ENOEXEC 722return value from 723.Xr execve 2 ) 724but appears to be a text file, 725the shell will run a new instance of 726.Nm 727to interpret it. 728.Pp 729Note that previous versions of this document 730and the source code itself misleadingly and sporadically 731refer to a shell script without a magic number 732as a 733.Dq "shell procedure" . 734.Ss Path Search 735When locating a command, the shell first looks to see if 736it has a shell function by that name. 737Then it looks for a 738built-in command by that name. 739If a built-in command is not found, 740one of two things happen: 741.Bl -enum 742.It 743Command names containing a slash are simply executed without 744performing any searches. 745.It 746The shell searches each entry in the 747.Va PATH 748variable 749in turn for the command. 750The value of the 751.Va PATH 752variable should be a series of 753entries separated by colons. 754Each entry consists of a 755directory name. 756The current directory 757may be indicated implicitly by an empty directory name, 758or explicitly by a single period. 759.El 760.Ss Command Exit Status 761Each command has an exit status that can influence the behavior 762of other shell commands. 763The paradigm is that a command exits 764with zero for normal or success, and non-zero for failure, 765error, or a false indication. 766The man page for each command 767should indicate the various exit codes and what they mean. 768Additionally, the built-in commands return exit codes, as does 769an executed shell function. 770.Pp 771If a command is terminated by a signal, its exit status is 128 plus 772the signal number. 773Signal numbers are defined in the header file 774.In sys/signal.h . 775.Ss Complex Commands 776Complex commands are combinations of simple commands 777with control operators or keywords, together creating a larger complex 778command. 779More generally, a command is one of the following: 780.Bl -item -offset indent 781.It 782simple command 783.It 784pipeline 785.It 786list or compound-list 787.It 788compound command 789.It 790function definition 791.El 792.Pp 793Unless otherwise stated, the exit status of a command is 794that of the last simple command executed by the command. 795.Ss Pipelines 796A pipeline is a sequence of one or more commands separated 797by the control operator 798.Ql \&| . 799The standard output of all but 800the last command is connected to the standard input 801of the next command. 802The standard output of the last 803command is inherited from the shell, as usual. 804.Pp 805The format for a pipeline is: 806.Pp 807.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... 808.Pp 809The standard output of 810.Ar command1 811is connected to the standard input of 812.Ar command2 . 813The standard input, standard output, or 814both of a command is considered to be assigned by the 815pipeline before any redirection specified by redirection 816operators that are part of the command. 817.Pp 818Note that unlike some other shells, 819.Nm 820executes each process in a pipeline with more than one command 821in a subshell environment and as a child of the 822.Nm 823process. 824.Pp 825If the pipeline is not in the background (discussed later), 826the shell waits for all commands to complete. 827.Pp 828If the keyword 829.Ic !\& 830does not precede the pipeline, the 831exit status is the exit status of the last command specified 832in the pipeline. 833Otherwise, the exit status is the logical 834NOT of the exit status of the last command. 835That is, if 836the last command returns zero, the exit status is 1; if 837the last command returns greater than zero, the exit status 838is zero. 839.Pp 840Because pipeline assignment of standard input or standard 841output or both takes place before redirection, it can be 842modified by redirection. 843For example: 844.Pp 845.Dl "command1 2>&1 | command2" 846.Pp 847sends both the standard output and standard error of 848.Ar command1 849to the standard input of 850.Ar command2 . 851.Pp 852A 853.Ql \&; 854or newline terminator causes the preceding 855AND-OR-list 856(described below in the section called 857.Sx Short-Circuit List Operators ) 858to be executed sequentially; 859an 860.Ql & 861causes asynchronous execution of the preceding AND-OR-list. 862.Ss Background Commands (&) 863If a command is terminated by the control operator ampersand 864.Pq Ql & , 865the shell executes the command in a subshell environment (see 866.Sx Grouping Commands Together 867below) and asynchronously; 868the shell does not wait for the command to finish 869before executing the next command. 870.Pp 871The format for running a command in background is: 872.Pp 873.D1 Ar command1 Li & Op Ar command2 Li & Ar ... 874.Pp 875If the shell is not interactive, the standard input of an 876asynchronous command is set to 877.Pa /dev/null . 878.Ss Lists (Generally Speaking) 879A list is a sequence of zero or more commands separated by 880newlines, semicolons, or ampersands, 881and optionally terminated by one of these three characters. 882The commands in a 883list are executed in the order they are written. 884If command is followed by an ampersand, the shell starts the 885command and immediately proceeds onto the next command; 886otherwise it waits for the command to terminate before 887proceeding to the next one. 888.Ss Short-Circuit List Operators 889.Dq Li && 890and 891.Dq Li || 892are AND-OR list operators. 893.Dq Li && 894executes the first command, and then executes the second command 895if the exit status of the first command is zero. 896.Dq Li || 897is similar, but executes the second command if the exit 898status of the first command is nonzero. 899.Dq Li && 900and 901.Dq Li || 902both have the same priority. 903.Ss Flow-Control Constructs (if, while, for, case) 904The syntax of the 905.Ic if 906command is: 907.Bd -unfilled -offset indent -compact 908.Ic if Ar list 909.Ic then Ar list 910.Oo Ic elif Ar list 911.Ic then Ar list Oc Ar ... 912.Op Ic else Ar list 913.Ic fi 914.Ed 915.Pp 916The syntax of the 917.Ic while 918command is: 919.Bd -unfilled -offset indent -compact 920.Ic while Ar list 921.Ic do Ar list 922.Ic done 923.Ed 924.Pp 925The two lists are executed repeatedly while the exit status of the 926first list is zero. 927The 928.Ic until 929command is similar, but has the word 930.Ic until 931in place of 932.Ic while , 933which causes it to 934repeat until the exit status of the first list is zero. 935.Pp 936The syntax of the 937.Ic for 938command is: 939.Bd -unfilled -offset indent -compact 940.Ic for Ar variable Op Ic in Ar word ... 941.Ic do Ar list 942.Ic done 943.Ed 944.Pp 945If 946.Ic in 947and the following words are omitted, 948.Ic in Li \&"$@\&" 949is used instead. 950The words are expanded, and then the list is executed 951repeatedly with the variable set to each word in turn. 952The 953.Ic do 954and 955.Ic done 956commands may be replaced with 957.Ql { 958and 959.Ql } . 960.Pp 961The syntax of the 962.Ic break 963and 964.Ic continue 965commands is: 966.D1 Ic break Op Ar num 967.D1 Ic continue Op Ar num 968.Pp 969The 970.Ic break 971command terminates the 972.Ar num 973innermost 974.Ic for 975or 976.Ic while 977loops. 978The 979.Ic continue 980command continues with the next iteration of the innermost loop. 981These are implemented as special built-in commands. 982.Pp 983The syntax of the 984.Ic case 985command is: 986.Bd -unfilled -offset indent -compact 987.Ic case Ar word Ic in 988.Ar pattern Ns Li ) Ar list Li ;; 989.Ar ... 990.Ic esac 991.Ed 992.Pp 993The pattern can actually be one or more patterns 994(see 995.Sx Shell Patterns 996described later), 997separated by 998.Ql \&| 999characters. 1000Tilde expansion, parameter expansion, command substitution, 1001arithmetic expansion and quote removal are applied to the word. 1002Then, each pattern is expanded in turn using tilde expansion, 1003parameter expansion, command substitution and arithmetic expansion and 1004the expanded form of the word is checked against it. 1005If a match is found, the corresponding list is executed. 1006If the selected list is terminated by the control operator 1007.Ql ;& 1008instead of 1009.Ql ;; , 1010execution continues with the next list, 1011continuing until a list terminated with 1012.Ql ;; 1013or the end of the 1014.Ic case 1015command. 1016The exit code of the 1017.Ic case 1018command is the exit code of the last command executed in the list or 1019zero if no patterns were matched. 1020.Ss Grouping Commands Together 1021Commands may be grouped by writing either 1022.Pp 1023.D1 Li \&( Ns Ar list Ns Li \%) 1024.Pp 1025or 1026.Pp 1027.D1 Li { Ar list Ns Li \&; } 1028.Pp 1029The first form executes the commands in a subshell environment. 1030A subshell environment has its own copy of: 1031.Bl -enum 1032.It 1033The current working directory as set by 1034.Ic cd . 1035.It 1036The file creation mask as set by 1037.Ic umask . 1038.It 1039Resource limits as set by 1040.Ic ulimit . 1041.It 1042References to open files. 1043.It 1044Traps as set by 1045.Ic trap . 1046.It 1047Known jobs. 1048.It 1049Positional parameters and variables. 1050.It 1051Shell options. 1052.It 1053Shell functions. 1054.It 1055Shell aliases. 1056.El 1057.Pp 1058These are copied from the parent shell environment, 1059except that trapped (but not ignored) signals are reset to the default action 1060and known jobs are cleared. 1061Any changes do not affect the parent shell environment. 1062.Pp 1063A subshell environment may be implemented as a child process or differently. 1064If job control is enabled in an interactive shell, 1065commands grouped in parentheses can be suspended and continued as a unit. 1066.Pp 1067For compatibility with other shells, 1068two open parentheses in sequence should be separated by whitespace. 1069.Pp 1070The second form never forks another shell, 1071so it is slightly more efficient. 1072Grouping commands together this way allows the user to 1073redirect their output as though they were one program: 1074.Bd -literal -offset indent 1075{ echo -n "hello"; echo " world"; } > greeting 1076.Ed 1077.Ss Functions 1078The syntax of a function definition is 1079.Pp 1080.D1 Ar name Li \&( \&) Ar command 1081.Pp 1082A function definition is an executable statement; when 1083executed it installs a function named 1084.Ar name 1085and returns an 1086exit status of zero. 1087The 1088.Ar command 1089is normally a list 1090enclosed between 1091.Ql { 1092and 1093.Ql } . 1094.Pp 1095Variables may be declared to be local to a function by 1096using the 1097.Ic local 1098command. 1099This should appear as the first statement of a function, 1100and the syntax is: 1101.Pp 1102.D1 Ic local Oo Ar variable ... Oc Op Fl 1103.Pp 1104The 1105.Ic local 1106command is implemented as a built-in command. 1107.Pp 1108When a variable is made local, it inherits the initial 1109value and exported and readonly flags from the variable 1110with the same name in the surrounding scope, if there is 1111one. 1112Otherwise, the variable is initially unset. 1113The shell 1114uses dynamic scoping, so that if the variable 1115.Va x 1116is made local to function 1117.Em f , 1118which then calls function 1119.Em g , 1120references to the variable 1121.Va x 1122made inside 1123.Em g 1124will refer to the variable 1125.Va x 1126declared inside 1127.Em f , 1128not to the global variable named 1129.Va x . 1130.Pp 1131The only special parameter that can be made local is 1132.Ql - . 1133Making 1134.Ql - 1135local causes any shell options that are 1136changed via the 1137.Ic set 1138command inside the function to be 1139restored to their original values when the function 1140returns. 1141.Pp 1142The syntax of the 1143.Ic return 1144command is 1145.Pp 1146.D1 Ic return Op Ar exitstatus 1147.Pp 1148It terminates the current executional scope, returning from the previous 1149nested function, sourced script, or shell instance, in that order. 1150The 1151.Ic return 1152command is implemented as a special built-in command. 1153.Ss Variables and Parameters 1154The shell maintains a set of parameters. 1155A parameter 1156denoted by a name is called a variable. 1157When starting up, 1158the shell turns all the environment variables into shell 1159variables. 1160New variables can be set using the form 1161.Pp 1162.D1 Ar name Ns = Ns Ar value 1163.Pp 1164Variables set by the user must have a name consisting solely 1165of alphabetics, numerics, and underscores. 1166The first letter of a variable name must not be numeric. 1167A parameter can also be denoted by a number 1168or a special character as explained below. 1169.Pp 1170Assignments are expanded differently from other words: 1171tilde expansion is also performed after the equals sign and after any colon 1172and usernames are also terminated by colons, 1173and field splitting and pathname expansion are not performed. 1174.Pp 1175This special expansion applies not only to assignments that form a simple 1176command by themselves or precede a command word, 1177but also to words passed to the 1178.Ic export , 1179.Ic local 1180or 1181.Ic readonly 1182built-in commands that have this form. 1183For this, the builtin's name must be literal 1184(not the result of an expansion) 1185and may optionally be preceded by one or more literal instances of 1186.Ic command 1187without options. 1188.Ss Positional Parameters 1189A positional parameter is a parameter denoted by a number greater than zero. 1190The shell sets these initially to the values of its command line 1191arguments that follow the name of the shell script. 1192The 1193.Ic set 1194built-in command can also be used to set or reset them. 1195.Ss Special Parameters 1196Special parameters are parameters denoted by a single special character 1197or the digit zero. 1198They are shown in the following list, exactly as they would appear in input 1199typed by the user or in the source of a shell script. 1200.Bl -hang 1201.It Li $* 1202Expands to the positional parameters, starting from one. 1203When 1204the expansion occurs within a double-quoted string 1205it expands to a single field with the value of each parameter 1206separated by the first character of the 1207.Va IFS 1208variable, 1209or by a space if 1210.Va IFS 1211is unset. 1212.It Li $@ 1213Expands to the positional parameters, starting from one. 1214When 1215the expansion occurs within double-quotes, each positional 1216parameter expands as a separate argument. 1217If there are no positional parameters, the 1218expansion of 1219.Li @ 1220generates zero arguments, even when 1221.Li @ 1222is double-quoted. 1223What this basically means, for example, is 1224if 1225.Li $1 1226is 1227.Dq Li abc 1228and 1229.Li $2 1230is 1231.Dq Li "def ghi" , 1232then 1233.Li \&"$@\&" 1234expands to 1235the two arguments: 1236.Bd -literal -offset indent 1237"abc" "def ghi" 1238.Ed 1239.It Li $# 1240Expands to the number of positional parameters. 1241.It Li $? 1242Expands to the exit status of the most recent pipeline. 1243.It Li $- 1244(hyphen) Expands to the current option flags (the single-letter 1245option names concatenated into a string) as specified on 1246invocation, by the 1247.Ic set 1248built-in command, or implicitly 1249by the shell. 1250.It Li $$ 1251Expands to the process ID of the invoked shell. 1252A subshell 1253retains the same value of 1254.Va $ 1255as its parent. 1256.It Li $! 1257Expands to the process ID of the most recent background 1258command executed from the current shell. 1259For a 1260pipeline, the process ID is that of the last command in the 1261pipeline. 1262If this parameter is referenced, the shell will remember 1263the process ID and its exit status until the 1264.Ic wait 1265built-in command reports completion of the process. 1266.It Li $0 1267(zero) Expands to the name of the shell script if passed on the command line, 1268the 1269.Ar name 1270operand if given (with 1271.Fl c ) 1272or otherwise argument 0 passed to the shell. 1273.El 1274.Ss Special Variables 1275The following variables are set by the shell or 1276have special meaning to it: 1277.Bl -tag -width ".Va HISTSIZE" 1278.It Va CDPATH 1279The search path used with the 1280.Ic cd 1281built-in. 1282.It Va EDITOR 1283The fallback editor used with the 1284.Ic fc 1285built-in. 1286If not set, the default editor is 1287.Xr ed 1 . 1288.It Va FCEDIT 1289The default editor used with the 1290.Ic fc 1291built-in. 1292.It Va HISTSIZE 1293The number of previous commands that are accessible. 1294.It Va HOME 1295The user's home directory, 1296used in tilde expansion and as a default directory for the 1297.Ic cd 1298built-in. 1299.It Va IFS 1300Input Field Separators. 1301The default value is 1302.Aq space , 1303.Aq tab , 1304and 1305.Aq newline 1306in that order. 1307This default also applies if 1308.Va IFS 1309is unset, but not if it is set to the empty string. 1310See the 1311.Sx White Space Splitting 1312section for more details. 1313.It Va LINENO 1314The current line number in the script or function. 1315.It Va MAIL 1316The name of a mail file, that will be checked for the arrival of new 1317mail. 1318Overridden by 1319.Va MAILPATH . 1320.It Va MAILPATH 1321A colon 1322.Pq Ql \&: 1323separated list of file names, for the shell to check for incoming 1324mail. 1325This variable overrides the 1326.Va MAIL 1327setting. 1328There is a maximum of 10 mailboxes that can be monitored at once. 1329.It Va PATH 1330The default search path for executables. 1331See the 1332.Sx Path Search 1333section for details. 1334.It Va PPID 1335The parent process ID of the invoked shell. 1336This is set at startup 1337unless this variable is in the environment. 1338A later change of parent process ID is not reflected. 1339A subshell retains the same value of 1340.Va PPID . 1341.It Va PS1 1342The primary prompt string, which defaults to 1343.Dq Li "$ " , 1344unless you are the superuser, in which case it defaults to 1345.Dq Li "# " . 1346.Va PS1 1347may include any of the following formatting sequences, 1348which are replaced by the given information: 1349.Bl -tag -width indent 1350.It Li \eH 1351The local hostname. 1352.It Li \eh 1353The fully-qualified hostname. 1354.It Li \eW 1355The final component of the current working directory. 1356.It Li \ew 1357The entire path of the current working directory. 1358.It Li \e$ 1359Superuser status. 1360.Dq Li "$ " 1361for normal users and 1362.Dq Li "# " 1363for superusers. 1364.It Li \e\e 1365A literal backslash. 1366.El 1367.It Va PS2 1368The secondary prompt string, which defaults to 1369.Dq Li "> " . 1370.Va PS2 1371may include any of the formatting sequences from 1372.Va PS1 . 1373.It Va PS4 1374The prefix for the trace output (if 1375.Fl x 1376is active). 1377The default is 1378.Dq Li "+ " . 1379.El 1380.Ss Word Expansions 1381This clause describes the various expansions that are 1382performed on words. 1383Not all expansions are performed on 1384every word, as explained later. 1385.Pp 1386Tilde expansions, parameter expansions, command substitutions, 1387arithmetic expansions, and quote removals that occur within 1388a single word expand to a single field. 1389It is only field 1390splitting or pathname expansion that can create multiple 1391fields from a single word. 1392The single exception to this rule is 1393the expansion of the special parameter 1394.Va @ 1395within double-quotes, 1396as was described above. 1397.Pp 1398The order of word expansion is: 1399.Bl -enum 1400.It 1401Tilde Expansion, Parameter Expansion, Command Substitution, 1402Arithmetic Expansion (these all occur at the same time). 1403.It 1404Field Splitting is performed on fields generated by step (1) 1405unless the 1406.Va IFS 1407variable is null. 1408.It 1409Pathname Expansion (unless the 1410.Fl f 1411option is in effect). 1412.It 1413Quote Removal. 1414.El 1415.Pp 1416The 1417.Ql $ 1418character is used to introduce parameter expansion, command 1419substitution, or arithmetic expansion. 1420.Ss Tilde Expansion (substituting a user's home directory) 1421A word beginning with an unquoted tilde character 1422.Pq Ql ~ 1423is 1424subjected to tilde expansion. 1425All the characters up to a slash 1426.Pq Ql / 1427or the end of the word are treated as a username 1428and are replaced with the user's home directory. 1429If the 1430username is missing (as in 1431.Pa ~/foobar ) , 1432the tilde is replaced with the value of the 1433.Va HOME 1434variable (the current user's home directory). 1435.Ss Parameter Expansion 1436The format for parameter expansion is as follows: 1437.Pp 1438.D1 Li ${ Ns Ar expression Ns Li } 1439.Pp 1440where 1441.Ar expression 1442consists of all characters until the matching 1443.Ql } . 1444Any 1445.Ql } 1446escaped by a backslash or within a single-quoted or double-quoted 1447string, and characters in 1448embedded arithmetic expansions, command substitutions, and variable 1449expansions, are not examined in determining the matching 1450.Ql } . 1451If the variants with 1452.Ql + , 1453.Ql - , 1454.Ql = 1455or 1456.Ql ?\& 1457occur within a double-quoted string, 1458as an extension there may be unquoted parts 1459(via double-quotes inside the expansion); 1460.Ql } 1461within such parts are also not examined in determining the matching 1462.Ql } . 1463.Pp 1464The simplest form for parameter expansion is: 1465.Pp 1466.D1 Li ${ Ns Ar parameter Ns Li } 1467.Pp 1468The value, if any, of 1469.Ar parameter 1470is substituted. 1471.Pp 1472The parameter name or symbol can be enclosed in braces, which are 1473optional except for positional parameters with more than one digit or 1474when parameter is followed by a character that could be interpreted as 1475part of the name. 1476If a parameter expansion occurs inside double-quotes: 1477.Bl -enum 1478.It 1479Field splitting is not performed on the results of the 1480expansion, with the exception of the special parameter 1481.Va @ . 1482.It 1483Pathname expansion is not performed on the results of the 1484expansion. 1485.El 1486.Pp 1487In addition, a parameter expansion can be modified by using one of the 1488following formats. 1489.Bl -tag -width indent 1490.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1491Use Default Values. 1492If 1493.Ar parameter 1494is unset or null, the expansion of 1495.Ar word 1496is substituted; otherwise, the value of 1497.Ar parameter 1498is substituted. 1499.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1500Assign Default Values. 1501If 1502.Ar parameter 1503is unset or null, the expansion of 1504.Ar word 1505is assigned to 1506.Ar parameter . 1507In all cases, the 1508final value of 1509.Ar parameter 1510is substituted. 1511Quoting inside 1512.Ar word 1513does not prevent field splitting or pathname expansion. 1514Only variables, not positional 1515parameters or special parameters, can be 1516assigned in this way. 1517.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1518Indicate Error if Null or Unset. 1519If 1520.Ar parameter 1521is unset or null, the expansion of 1522.Ar word 1523(or a message indicating it is unset if 1524.Ar word 1525is omitted) is written to standard 1526error and the shell exits with a nonzero 1527exit status. 1528Otherwise, the value of 1529.Ar parameter 1530is substituted. 1531An 1532interactive shell need not exit. 1533.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1534Use Alternate Value. 1535If 1536.Ar parameter 1537is unset or null, null is substituted; 1538otherwise, the expansion of 1539.Ar word 1540is substituted. 1541.El 1542.Pp 1543In the parameter expansions shown previously, use of the colon in the 1544format results in a test for a parameter that is unset or null; omission 1545of the colon results in a test for a parameter that is only unset. 1546.Pp 1547The 1548.Ar word 1549inherits the type of quoting 1550(unquoted, double-quoted or here-document) 1551from the surroundings, 1552with the exception that a backslash that quotes a closing brace is removed 1553during quote removal. 1554.Bl -tag -width indent 1555.It Li ${# Ns Ar parameter Ns Li } 1556String Length. 1557The length in characters of 1558the value of 1559.Ar parameter . 1560.El 1561.Pp 1562The following four varieties of parameter expansion provide for substring 1563processing. 1564In each case, pattern matching notation 1565(see 1566.Sx Shell Patterns ) , 1567rather than regular expression notation, 1568is used to evaluate the patterns. 1569If parameter is one of the special parameters 1570.Va * 1571or 1572.Va @ , 1573the result of the expansion is unspecified. 1574Enclosing the full parameter expansion string in double-quotes does not 1575cause the following four varieties of pattern characters to be quoted, 1576whereas quoting characters within the braces has this effect. 1577.Bl -tag -width indent 1578.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1579Remove Smallest Suffix Pattern. 1580The 1581.Ar word 1582is expanded to produce a pattern. 1583The 1584parameter expansion then results in 1585.Ar parameter , 1586with the smallest portion of the 1587suffix matched by the pattern deleted. 1588.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1589Remove Largest Suffix Pattern. 1590The 1591.Ar word 1592is expanded to produce a pattern. 1593The 1594parameter expansion then results in 1595.Ar parameter , 1596with the largest portion of the 1597suffix matched by the pattern deleted. 1598.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1599Remove Smallest Prefix Pattern. 1600The 1601.Ar word 1602is expanded to produce a pattern. 1603The 1604parameter expansion then results in 1605.Ar parameter , 1606with the smallest portion of the 1607prefix matched by the pattern deleted. 1608.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1609Remove Largest Prefix Pattern. 1610The 1611.Ar word 1612is expanded to produce a pattern. 1613The 1614parameter expansion then results in 1615.Ar parameter , 1616with the largest portion of the 1617prefix matched by the pattern deleted. 1618.El 1619.Ss Command Substitution 1620Command substitution allows the output of a command to be substituted in 1621place of the command name itself. 1622Command substitution occurs when 1623the command is enclosed as follows: 1624.Pp 1625.D1 Li $( Ns Ar command Ns Li )\& 1626.Pp 1627or the backquoted version: 1628.Pp 1629.D1 Li ` Ns Ar command Ns Li ` 1630.Pp 1631The shell expands the command substitution by executing command 1632and replacing the command substitution 1633with the standard output of the command, 1634removing sequences of one or more newlines at the end of the substitution. 1635Embedded newlines before the end of the output are not removed; 1636however, during field splitting, they may be translated into spaces 1637depending on the value of 1638.Va IFS 1639and the quoting that is in effect. 1640The command is executed in a subshell environment, 1641except that the built-in commands 1642.Ic jobid , 1643.Ic jobs , 1644and 1645.Ic trap 1646return information about the parent shell environment 1647and 1648.Ic times 1649returns information about the same process 1650if they are the only command in a command substitution. 1651.Pp 1652If a command substitution of the 1653.Li $( 1654form begins with a subshell, 1655the 1656.Li $( 1657and 1658.Li (\& 1659must be separated by whitespace 1660to avoid ambiguity with arithmetic expansion. 1661.Ss Arithmetic Expansion 1662Arithmetic expansion provides a mechanism for evaluating an arithmetic 1663expression and substituting its value. 1664The format for arithmetic expansion is as follows: 1665.Pp 1666.D1 Li $(( Ns Ar expression Ns Li )) 1667.Pp 1668The 1669.Ar expression 1670is treated as if it were in double-quotes, except 1671that a double-quote inside the expression is not treated specially. 1672The 1673shell expands all tokens in the 1674.Ar expression 1675for parameter expansion, 1676command substitution, 1677arithmetic expansion 1678and quote removal. 1679.Pp 1680The allowed expressions are a subset of C expressions, 1681summarized below. 1682.Bl -tag -width "Variables" -offset indent 1683.It Values 1684All values are of type 1685.Ft intmax_t . 1686.It Constants 1687Decimal, octal (starting with 1688.Li 0 ) 1689and hexadecimal (starting with 1690.Li 0x ) 1691integer constants. 1692.It Variables 1693Shell variables can be read and written 1694and contain integer constants. 1695.It Unary operators 1696.Li "! ~ + -" 1697.It Binary operators 1698.Li "* / % + - << >> < <= > >= == != & ^ | && ||" 1699.It Assignment operators 1700.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1701.It Conditional operator 1702.Li "? :" 1703.El 1704.Pp 1705The result of the expression is substituted in decimal. 1706.Ss White Space Splitting (Field Splitting) 1707In certain contexts, 1708after parameter expansion, command substitution, and 1709arithmetic expansion the shell scans the results of 1710expansions and substitutions that did not occur in double-quotes for 1711field splitting and multiple fields can result. 1712.Pp 1713Characters in 1714.Va IFS 1715that are whitespace 1716.Po 1717.Aq space , 1718.Aq tab , 1719and 1720.Aq newline 1721.Pc 1722are treated differently from other characters in 1723.Va IFS . 1724.Pp 1725Whitespace in 1726.Va IFS 1727at the beginning or end of a word is discarded. 1728.Pp 1729Subsequently, a field is delimited by either 1730.Bl -enum 1731.It 1732a non-whitespace character in 1733.Va IFS 1734with any whitespace in 1735.Va IFS 1736surrounding it, or 1737.It 1738one or more whitespace characters in 1739.Va IFS . 1740.El 1741.Pp 1742If a word ends with a non-whitespace character in 1743.Va IFS , 1744there is no empty field after this character. 1745.Pp 1746If no field is delimited, the word is discarded. 1747In particular, if a word consists solely of an unquoted substitution 1748and the result of the substitution is null, 1749it is removed by field splitting even if 1750.Va IFS 1751is null. 1752.Ss Pathname Expansion (File Name Generation) 1753Unless the 1754.Fl f 1755option is set, 1756file name generation is performed 1757after word splitting is complete. 1758Each word is 1759viewed as a series of patterns, separated by slashes. 1760The 1761process of expansion replaces the word with the names of 1762all existing files whose names can be formed by replacing 1763each pattern with a string that matches the specified pattern. 1764There are two restrictions on this: first, a pattern cannot match 1765a string containing a slash, and second, 1766a pattern cannot match a string starting with a period 1767unless the first character of the pattern is a period. 1768The next section describes the patterns used for 1769Pathname Expansion, 1770the four varieties of parameter expansion for substring processing and the 1771.Ic case 1772command. 1773.Ss Shell Patterns 1774A pattern consists of normal characters, which match themselves, 1775and meta-characters. 1776The meta-characters are 1777.Ql * , 1778.Ql \&? , 1779and 1780.Ql \&[ . 1781These characters lose their special meanings if they are quoted. 1782When command or variable substitution is performed and the dollar sign 1783or back quotes are not double-quoted, the value of the 1784variable or the output of the command is scanned for these 1785characters and they are turned into meta-characters. 1786.Pp 1787An asterisk 1788.Pq Ql * 1789matches any string of characters. 1790A question mark 1791.Pq Ql \&? 1792matches any single character. 1793A left bracket 1794.Pq Ql \&[ 1795introduces a character class. 1796The end of the character class is indicated by a 1797.Ql \&] ; 1798if the 1799.Ql \&] 1800is missing then the 1801.Ql \&[ 1802matches a 1803.Ql \&[ 1804rather than introducing a character class. 1805A character class matches any of the characters between the square brackets. 1806A locale-dependent range of characters may be specified using a minus sign. 1807A named class of characters (see 1808.Xr wctype 3 ) 1809may be specified by surrounding the name with 1810.Ql \&[: 1811and 1812.Ql :\&] . 1813For example, 1814.Ql \&[\&[:alpha:\&]\&] 1815is a shell pattern that matches a single letter. 1816The character class may be complemented by making an exclamation point 1817.Pq Ql !\& 1818the first character of the character class. 1819A caret 1820.Pq Ql ^ 1821has the same effect but is non-standard. 1822.Pp 1823To include a 1824.Ql \&] 1825in a character class, make it the first character listed 1826(after the 1827.Ql \&! 1828or 1829.Ql ^ , 1830if any). 1831To include a 1832.Ql - , 1833make it the first or last character listed. 1834.Ss Built-in Commands 1835This section lists the built-in commands. 1836.Bl -tag -width indent 1837.It Ic \&: 1838A null command that returns a 0 (true) exit value. 1839.It Ic \&. Ar file 1840The commands in the specified file are read and executed by the shell. 1841The 1842.Ic return 1843command may be used to return to the 1844.Ic \&. 1845command's caller. 1846If 1847.Ar file 1848contains any 1849.Ql / 1850characters, it is used as is. 1851Otherwise, the shell searches the 1852.Va PATH 1853for the file. 1854If it is not found in the 1855.Va PATH , 1856it is sought in the current working directory. 1857.It Ic \&[ 1858A built-in equivalent of 1859.Xr test 1 . 1860.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc 1861If 1862.Ar name Ns = Ns Ar string 1863is specified, the shell defines the alias 1864.Ar name 1865with value 1866.Ar string . 1867If just 1868.Ar name 1869is specified, the value of the alias 1870.Ar name 1871is printed. 1872With no arguments, the 1873.Ic alias 1874built-in command prints the names and values of all defined aliases 1875(see 1876.Ic unalias ) . 1877Alias values are written with appropriate quoting so that they are 1878suitable for re-input to the shell. 1879Also see the 1880.Sx Aliases 1881subsection. 1882.It Ic bg Op Ar job ... 1883Continue the specified jobs 1884(or the current job if no jobs are given) 1885in the background. 1886.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1887List or alter key bindings for the line editor. 1888This command is documented in 1889.Xr editrc 5 . 1890.It Ic break Op Ar num 1891See the 1892.Sx Flow-Control Constructs 1893subsection. 1894.It Ic builtin Ar cmd Op Ar arg ... 1895Execute the specified built-in command, 1896.Ar cmd . 1897This is useful when the user wishes to override a shell function 1898with the same name as a built-in command. 1899.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 1900Switch to the specified 1901.Ar directory , 1902or to the directory specified in the 1903.Va HOME 1904environment variable if no 1905.Ar directory 1906is specified. 1907If 1908.Ar directory 1909does not begin with 1910.Pa / , \&. , 1911or 1912.Pa .. , 1913then the directories listed in the 1914.Va CDPATH 1915variable will be 1916searched for the specified 1917.Ar directory . 1918If 1919.Va CDPATH 1920is unset, the current directory is searched. 1921The format of 1922.Va CDPATH 1923is the same as that of 1924.Va PATH . 1925In an interactive shell, 1926the 1927.Ic cd 1928command will print out the name of the directory 1929that it actually switched to 1930if this is different from the name that the user gave. 1931These may be different either because the 1932.Va CDPATH 1933mechanism was used or because a symbolic link was crossed. 1934.Pp 1935If the 1936.Fl P 1937option is specified, 1938.Pa .. 1939is handled physically and symbolic links are resolved before 1940.Pa .. 1941components are processed. 1942If the 1943.Fl L 1944option is specified, 1945.Pa .. 1946is handled logically. 1947This is the default. 1948.Pp 1949The 1950.Fl e 1951option causes 1952.Ic cd 1953to return exit status 1 if the full pathname of the new directory 1954cannot be determined reliably or at all. 1955Normally this is not considered an error, 1956although a warning is printed. 1957.It Ic chdir 1958A synonym for the 1959.Ic cd 1960built-in command. 1961.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 1962.It Ic command Oo Fl p Oc Fl v Ar utility 1963.It Ic command Oo Fl p Oc Fl V Ar utility 1964The first form of invocation executes the specified 1965.Ar utility , 1966ignoring shell functions in the search. 1967If 1968.Ar utility 1969is a special builtin, 1970it is executed as if it were a regular builtin. 1971.Pp 1972If the 1973.Fl p 1974option is specified, the command search is performed using a 1975default value of 1976.Va PATH 1977that is guaranteed to find all of the standard utilities. 1978.Pp 1979If the 1980.Fl v 1981option is specified, 1982.Ar utility 1983is not executed but a description of its interpretation by the shell is 1984printed. 1985For ordinary commands the output is the path name; for shell built-in 1986commands, shell functions and keywords only the name is written. 1987Aliases are printed as 1988.Dq Ic alias Ar name Ns = Ns Ar value . 1989.Pp 1990The 1991.Fl V 1992option is identical to 1993.Fl v 1994except for the output. 1995It prints 1996.Dq Ar utility Ic is Ar description 1997where 1998.Ar description 1999is either 2000the path name to 2001.Ar utility , 2002a special shell builtin, 2003a shell builtin, 2004a shell function, 2005a shell keyword 2006or 2007an alias for 2008.Ar value . 2009.It Ic continue Op Ar num 2010See the 2011.Sx Flow-Control Constructs 2012subsection. 2013.It Ic echo Oo Fl e | n Oc Op Ar string ... 2014Print a space-separated list of the arguments to the standard output 2015and append a newline character. 2016.Bl -tag -width indent 2017.It Fl n 2018Suppress the output of the trailing newline. 2019.It Fl e 2020Process C-style backslash escape sequences. 2021The 2022.Ic echo 2023command understands the following character escapes: 2024.Bl -tag -width indent 2025.It \ea 2026Alert (ring the terminal bell) 2027.It \eb 2028Backspace 2029.It \ec 2030Suppress the trailing newline (this has the side-effect of truncating the 2031line if it is not the last character) 2032.It \ee 2033The ESC character 2034.Tn ( ASCII 20350x1b) 2036.It \ef 2037Formfeed 2038.It \en 2039Newline 2040.It \er 2041Carriage return 2042.It \et 2043Horizontal tab 2044.It \ev 2045Vertical tab 2046.It \e\e 2047Literal backslash 2048.It \e0nnn 2049(Zero) The character whose octal value is 2050.Ar nnn 2051.El 2052.Pp 2053If 2054.Ar string 2055is not enclosed in quotes then the backslash itself must be escaped 2056with a backslash to protect it from the shell. 2057For example 2058.Bd -literal -offset indent 2059$ echo -e "a\evb" 2060a 2061 b 2062$ echo -e a\e\evb 2063a 2064 b 2065$ echo -e "a\e\eb" 2066a\eb 2067$ echo -e a\e\e\e\eb 2068a\eb 2069.Ed 2070.El 2071.Pp 2072Only one of the 2073.Fl e 2074and 2075.Fl n 2076options may be specified. 2077.It Ic eval Ar string ... 2078Concatenate all the arguments with spaces. 2079Then re-parse and execute the command. 2080.It Ic exec Op Ar command Op arg ... 2081Unless 2082.Ar command 2083is omitted, 2084the shell process is replaced with the specified program 2085(which must be a real program, not a shell built-in command or function). 2086Any redirections on the 2087.Ic exec 2088command are marked as permanent, 2089so that they are not undone when the 2090.Ic exec 2091command finishes. 2092.It Ic exit Op Ar exitstatus 2093Terminate the shell process. 2094If 2095.Ar exitstatus 2096is given 2097it is used as the exit status of the shell. 2098Otherwise, if the shell is executing an 2099.Cm EXIT 2100trap, the exit status of the last command before the trap is used; 2101if the shell is executing a trap for a signal, 2102the shell exits by resending the signal to itself. 2103Otherwise, the exit status of the preceding command is used. 2104The exit status should be an integer between 0 and 255. 2105.It Ic export Ar name ... 2106.It Ic export Op Fl p 2107The specified names are exported so that they will 2108appear in the environment of subsequent commands. 2109The only way to un-export a variable is to 2110.Ic unset 2111it. 2112The shell allows the value of a variable to be set 2113at the same time as it is exported by writing 2114.Pp 2115.D1 Ic export Ar name Ns = Ns Ar value 2116.Pp 2117With no arguments the 2118.Ic export 2119command lists the names 2120of all exported variables. 2121If the 2122.Fl p 2123option is specified, the exported variables are printed as 2124.Dq Ic export Ar name Ns = Ns Ar value 2125lines, suitable for re-input to the shell. 2126.It Ic false 2127A null command that returns a non-zero (false) exit value. 2128.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2129.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2130.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2131The 2132.Ic fc 2133built-in command lists, or edits and re-executes, 2134commands previously entered to an interactive shell. 2135.Bl -tag -width indent 2136.It Fl e Ar editor 2137Use the editor named by 2138.Ar editor 2139to edit the commands. 2140The 2141.Ar editor 2142string is a command name, 2143subject to search via the 2144.Va PATH 2145variable. 2146The value in the 2147.Va FCEDIT 2148variable is used as a default when 2149.Fl e 2150is not specified. 2151If 2152.Va FCEDIT 2153is null or unset, the value of the 2154.Va EDITOR 2155variable is used. 2156If 2157.Va EDITOR 2158is null or unset, 2159.Xr ed 1 2160is used as the editor. 2161.It Fl l No (ell) 2162List the commands rather than invoking 2163an editor on them. 2164The commands are written in the 2165sequence indicated by the 2166.Ar first 2167and 2168.Ar last 2169operands, as affected by 2170.Fl r , 2171with each command preceded by the command number. 2172.It Fl n 2173Suppress command numbers when listing with 2174.Fl l . 2175.It Fl r 2176Reverse the order of the commands listed 2177(with 2178.Fl l ) 2179or edited 2180(with neither 2181.Fl l 2182nor 2183.Fl s ) . 2184.It Fl s 2185Re-execute the command without invoking an editor. 2186.It Ar first 2187.It Ar last 2188Select the commands to list or edit. 2189The number of previous commands that can be accessed 2190are determined by the value of the 2191.Va HISTSIZE 2192variable. 2193The value of 2194.Ar first 2195or 2196.Ar last 2197or both are one of the following: 2198.Bl -tag -width indent 2199.It Oo Cm + Oc Ns Ar num 2200A positive number representing a command number; 2201command numbers can be displayed with the 2202.Fl l 2203option. 2204.It Fl Ar num 2205A negative decimal number representing the 2206command that was executed 2207.Ar num 2208of 2209commands previously. 2210For example, \-1 is the immediately previous command. 2211.It Ar string 2212A string indicating the most recently entered command 2213that begins with that string. 2214If the 2215.Ar old Ns = Ns Ar new 2216operand is not also specified with 2217.Fl s , 2218the string form of the first operand cannot contain an embedded equal sign. 2219.El 2220.El 2221.Pp 2222The following variables affect the execution of 2223.Ic fc : 2224.Bl -tag -width ".Va HISTSIZE" 2225.It Va FCEDIT 2226Name of the editor to use for history editing. 2227.It Va HISTSIZE 2228The number of previous commands that are accessible. 2229.El 2230.It Ic fg Op Ar job 2231Move the specified 2232.Ar job 2233or the current job to the foreground. 2234.It Ic getopts Ar optstring var 2235The 2236.Tn POSIX 2237.Ic getopts 2238command. 2239The 2240.Ic getopts 2241command deprecates the older 2242.Xr getopt 1 2243command. 2244The first argument should be a series of letters, each possibly 2245followed by a colon which indicates that the option takes an argument. 2246The specified variable is set to the parsed option. 2247The index of 2248the next argument is placed into the shell variable 2249.Va OPTIND . 2250If an option takes an argument, it is placed into the shell variable 2251.Va OPTARG . 2252If an invalid option is encountered, 2253.Ar var 2254is set to 2255.Ql \&? . 2256It returns a false value (1) when it encounters the end of the options. 2257.It Ic hash Oo Fl rv Oc Op Ar command ... 2258The shell maintains a hash table which remembers the locations of commands. 2259With no arguments whatsoever, the 2260.Ic hash 2261command prints out the contents of this table. 2262.Pp 2263With arguments, the 2264.Ic hash 2265command removes each specified 2266.Ar command 2267from the hash table (unless they are functions) and then locates it. 2268With the 2269.Fl v 2270option, 2271.Ic hash 2272prints the locations of the commands as it finds them. 2273The 2274.Fl r 2275option causes the 2276.Ic hash 2277command to delete all the entries in the hash table except for functions. 2278.It Ic jobid Op Ar job 2279Print the process IDs of the processes in the specified 2280.Ar job . 2281If the 2282.Ar job 2283argument is omitted, use the current job. 2284.It Ic jobs Oo Fl lps Oc Op Ar job ... 2285Print information about the specified jobs, or all jobs if no 2286.Ar job 2287argument is given. 2288The information printed includes job ID, status and command name. 2289.Pp 2290If the 2291.Fl l 2292option is specified, the PID of each job is also printed. 2293If the 2294.Fl p 2295option is specified, only the process IDs for the process group leaders 2296are printed, one per line. 2297If the 2298.Fl s 2299option is specified, only the PIDs of the job commands are printed, one per 2300line. 2301.It Ic kill 2302A built-in equivalent of 2303.Xr kill 1 2304that additionally supports sending signals to jobs. 2305.It Ic local Oo Ar variable ... Oc Op Fl 2306See the 2307.Sx Functions 2308subsection. 2309.It Ic printf 2310A built-in equivalent of 2311.Xr printf 1 . 2312.It Ic pwd Op Fl L | P 2313Print the path of the current directory. 2314The built-in command may 2315differ from the program of the same name because the 2316built-in command remembers what the current directory 2317is rather than recomputing it each time. 2318This makes 2319it faster. 2320However, if the current directory is 2321renamed, 2322the built-in version of 2323.Xr pwd 1 2324will continue to print the old name for the directory. 2325.Pp 2326If the 2327.Fl P 2328option is specified, symbolic links are resolved. 2329If the 2330.Fl L 2331option is specified, the shell's notion of the current directory 2332is printed (symbolic links are not resolved). 2333This is the default. 2334.It Ic read Oo Fl p Ar prompt Oc Oo 2335.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2336The 2337.Ar prompt 2338is printed if the 2339.Fl p 2340option is specified 2341and the standard input is a terminal. 2342Then a line is 2343read from the standard input. 2344The trailing newline 2345is deleted from the line and the line is split as 2346described in the section on 2347.Sx White Space Splitting (Field Splitting) 2348above, and 2349the pieces are assigned to the variables in order. 2350If there are more pieces than variables, the remaining 2351pieces (along with the characters in 2352.Va IFS 2353that separated them) 2354are assigned to the last variable. 2355If there are more variables than pieces, the remaining 2356variables are assigned the null string. 2357.Pp 2358Backslashes are treated specially, unless the 2359.Fl r 2360option is 2361specified. 2362If a backslash is followed by 2363a newline, the backslash and the newline will be 2364deleted. 2365If a backslash is followed by any other 2366character, the backslash will be deleted and the following 2367character will be treated as though it were not in 2368.Va IFS , 2369even if it is. 2370.Pp 2371If the 2372.Fl t 2373option is specified and the 2374.Ar timeout 2375elapses before a complete line of input is supplied, 2376the 2377.Ic read 2378command will return an exit status as if terminated by 2379.Dv SIGALRM 2380without assigning any values. 2381The 2382.Ar timeout 2383value may optionally be followed by one of 2384.Ql s , 2385.Ql m 2386or 2387.Ql h 2388to explicitly specify seconds, minutes or hours. 2389If none is supplied, 2390.Ql s 2391is assumed. 2392.Pp 2393The 2394.Fl e 2395option exists only for backward compatibility with older scripts. 2396.Pp 2397The exit status is 0 on success, 1 on end of file, 2398between 2 and 128 if an error occurs 2399and greater than 128 if a trapped signal interrupts 2400.Ic read . 2401.It Ic readonly Oo Fl p Oc Op Ar name ... 2402Each specified 2403.Ar name 2404is marked as read only, 2405so that it cannot be subsequently modified or unset. 2406The shell allows the value of a variable to be set 2407at the same time as it is marked read only 2408by using the following form: 2409.Pp 2410.D1 Ic readonly Ar name Ns = Ns Ar value 2411.Pp 2412With no arguments the 2413.Ic readonly 2414command lists the names of all read only variables. 2415If the 2416.Fl p 2417option is specified, the read-only variables are printed as 2418.Dq Ic readonly Ar name Ns = Ns Ar value 2419lines, suitable for re-input to the shell. 2420.It Ic return Op Ar exitstatus 2421See the 2422.Sx Functions 2423subsection. 2424.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 2425.Fl c Ar string Oc Op Fl - Ar arg ... 2426The 2427.Ic set 2428command performs three different functions: 2429.Bl -item 2430.It 2431With no arguments, it lists the values of all shell variables. 2432.It 2433If options are given, 2434either in short form or using the long 2435.Dq Fl /+o Ar longname 2436form, 2437it sets or clears the specified options as described in the section called 2438.Sx Argument List Processing . 2439.It 2440If the 2441.Dq Fl - 2442option is specified, 2443.Ic set 2444will replace the shell's positional parameters with the subsequent 2445arguments. 2446If no arguments follow the 2447.Dq Fl - 2448option, 2449all the positional parameters will be cleared, 2450which is equivalent to executing the command 2451.Dq Li "shift $#" . 2452The 2453.Dq Fl - 2454flag may be omitted when specifying arguments to be used 2455as positional replacement parameters. 2456This is not recommended, 2457because the first argument may begin with a dash 2458.Pq Ql - 2459or a plus 2460.Pq Ql + , 2461which the 2462.Ic set 2463command will interpret as a request to enable or disable options. 2464.El 2465.It Ic setvar Ar variable value 2466Assigns the specified 2467.Ar value 2468to the specified 2469.Ar variable . 2470The 2471.Ic setvar 2472command is intended to be used in functions that 2473assign values to variables whose names are passed as parameters. 2474In general it is better to write 2475.Dq Ar variable Ns = Ns Ar value 2476rather than using 2477.Ic setvar . 2478.It Ic shift Op Ar n 2479Shift the positional parameters 2480.Ar n 2481times, or once if 2482.Ar n 2483is not specified. 2484A shift sets the value of 2485.Li $1 2486to the value of 2487.Li $2 , 2488the value of 2489.Li $2 2490to the value of 2491.Li $3 , 2492and so on, 2493decreasing the value of 2494.Li $# 2495by one. 2496If there are zero positional parameters, shifting does not do anything. 2497.It Ic test 2498A built-in equivalent of 2499.Xr test 1 . 2500.It Ic times 2501Print the amount of time spent executing the shell process and its children. 2502The first output line shows the user and system times for the shell process 2503itself, the second one contains the user and system times for the 2504children. 2505.It Ic trap Oo Ar action Oc Ar signal ... 2506.It Ic trap Fl l 2507Cause the shell to parse and execute 2508.Ar action 2509when any specified 2510.Ar signal 2511is received. 2512The signals are specified by name or number. 2513In addition, the pseudo-signal 2514.Cm EXIT 2515may be used to specify an 2516.Ar action 2517that is performed when the shell terminates. 2518The 2519.Ar action 2520may be an empty string or a dash 2521.Pq Ql - ; 2522the former causes the specified signal to be ignored 2523and the latter causes the default action to be taken. 2524Omitting the 2525.Ar action 2526is another way to request the default action, for compatibility reasons this 2527usage is not recommended though. 2528In a subshell or utility environment, 2529the shell resets trapped (but not ignored) signals to the default action. 2530The 2531.Ic trap 2532command has no effect on signals that were ignored on entry to the shell. 2533.Pp 2534Option 2535.Fl l 2536causes the 2537.Ic trap 2538command to display a list of valid signal names. 2539.It Ic true 2540A null command that returns a 0 (true) exit value. 2541.It Ic type Op Ar name ... 2542Interpret each 2543.Ar name 2544as a command and print the resolution of the command search. 2545Possible resolutions are: 2546shell keyword, alias, special shell builtin, shell builtin, command, 2547tracked alias 2548and not found. 2549For aliases the alias expansion is printed; 2550for commands and tracked aliases 2551the complete pathname of the command is printed. 2552.It Ic ulimit Oo Fl HSabcdflmnpstuvw Oc Op Ar limit 2553Set or display resource limits (see 2554.Xr getrlimit 2 ) . 2555If 2556.Ar limit 2557is specified, the named resource will be set; 2558otherwise the current resource value will be displayed. 2559.Pp 2560If 2561.Fl H 2562is specified, the hard limits will be set or displayed. 2563While everybody is allowed to reduce a hard limit, 2564only the superuser can increase it. 2565The 2566.Fl S 2567option 2568specifies the soft limits instead. 2569When displaying limits, 2570only one of 2571.Fl S 2572or 2573.Fl H 2574can be given. 2575The default is to display the soft limits, 2576and to set both the hard and the soft limits. 2577.Pp 2578Option 2579.Fl a 2580causes the 2581.Ic ulimit 2582command to display all resources. 2583The parameter 2584.Ar limit 2585is not acceptable in this mode. 2586.Pp 2587The remaining options specify which resource value is to be 2588displayed or modified. 2589They are mutually exclusive. 2590.Bl -tag -width indent 2591.It Fl b Ar sbsize 2592The maximum size of socket buffer usage, in bytes. 2593.It Fl c Ar coredumpsize 2594The maximal size of core dump files, in 512-byte blocks. 2595.It Fl d Ar datasize 2596The maximal size of the data segment of a process, in kilobytes. 2597.It Fl f Ar filesize 2598The maximal size of a file, in 512-byte blocks. 2599.It Fl l Ar lockedmem 2600The maximal size of memory that can be locked by a process, in 2601kilobytes. 2602.It Fl m Ar memoryuse 2603The maximal resident set size of a process, in kilobytes. 2604.It Fl n Ar nofiles 2605The maximal number of descriptors that could be opened by a process. 2606.It Fl p Ar pseudoterminals 2607The maximal number of pseudo-terminals for this user ID. 2608.It Fl s Ar stacksize 2609The maximal size of the stack segment, in kilobytes. 2610.It Fl t Ar time 2611The maximal amount of CPU time to be used by each process, in seconds. 2612.It Fl u Ar userproc 2613The maximal number of simultaneous processes for this user ID. 2614.It Fl v Ar virtualmem 2615The maximal virtual size of a process, in kilobytes. 2616.It Fl w Ar swapuse 2617The maximum amount of swap space reserved or used for this user ID, 2618in kilobytes. 2619.El 2620.It Ic umask Oo Fl S Oc Op Ar mask 2621Set the file creation mask (see 2622.Xr umask 2 ) 2623to the octal or symbolic (see 2624.Xr chmod 1 ) 2625value specified by 2626.Ar mask . 2627If the argument is omitted, the current mask value is printed. 2628If the 2629.Fl S 2630option is specified, the output is symbolic, otherwise the output is octal. 2631.It Ic unalias Oo Fl a Oc Op Ar name ... 2632The specified alias names are removed. 2633If 2634.Fl a 2635is specified, all aliases are removed. 2636.It Ic unset Oo Fl fv Oc Ar name ... 2637The specified variables or functions are unset and unexported. 2638If the 2639.Fl v 2640option is specified or no options are given, the 2641.Ar name 2642arguments are treated as variable names. 2643If the 2644.Fl f 2645option is specified, the 2646.Ar name 2647arguments are treated as function names. 2648.It Ic wait Op Ar job ... 2649Wait for each specified 2650.Ar job 2651to complete and return the exit status of the last process in the 2652last specified 2653.Ar job . 2654If any 2655.Ar job 2656specified is unknown to the shell, it is treated as if it 2657were a known job that exited with exit status 127. 2658If no operands are given, wait for all jobs to complete 2659and return an exit status of zero. 2660.El 2661.Ss Commandline Editing 2662When 2663.Nm 2664is being used interactively from a terminal, the current command 2665and the command history 2666(see 2667.Ic fc 2668in 2669.Sx Built-in Commands ) 2670can be edited using 2671.Nm vi Ns -mode 2672command line editing. 2673This mode uses commands similar 2674to a subset of those described in the 2675.Xr vi 1 2676man page. 2677The command 2678.Dq Li "set -o vi" 2679(or 2680.Dq Li "set -V" ) 2681enables 2682.Nm vi Ns -mode 2683editing and places 2684.Nm 2685into 2686.Nm vi 2687insert mode. 2688With 2689.Nm vi Ns -mode 2690enabled, 2691.Nm 2692can be switched between insert mode and command mode by typing 2693.Aq ESC . 2694Hitting 2695.Aq return 2696while in command mode will pass the line to the shell. 2697.Pp 2698Similarly, the 2699.Dq Li "set -o emacs" 2700(or 2701.Dq Li "set -E" ) 2702command can be used to enable a subset of 2703.Nm emacs Ns -style 2704command line editing features. 2705.Sh ENVIRONMENT 2706The following environment variables affect the execution of 2707.Nm : 2708.Bl -tag -width ".Ev LANGXXXXXX" 2709.It Ev ENV 2710Initialization file for interactive shells. 2711.It Ev LANG , Ev LC_* 2712Locale settings. 2713These are inherited by children of the shell, 2714and is used in a limited manner by the shell itself. 2715.It Ev PWD 2716An absolute pathname for the current directory, 2717possibly containing symbolic links. 2718This is used and updated by the shell. 2719.It Ev TERM 2720The default terminal setting for the shell. 2721This is inherited by children of the shell, and is used in the history 2722editing modes. 2723.El 2724.Pp 2725Additionally, all environment variables are turned into shell variables 2726at startup, 2727which may affect the shell as described under 2728.Sx Special Variables . 2729.Sh FILES 2730.Bl -tag -width "/etc/suid_profileXX" -compact 2731.It Pa ~/.profile 2732User's login profile. 2733.It Pa /etc/profile 2734System login profile. 2735.It Pa /etc/shells 2736Shell database. 2737.It Pa /etc/suid_profile 2738Privileged shell profile. 2739.El 2740.Sh EXIT STATUS 2741Errors that are detected by the shell, such as a syntax error, will 2742cause the shell to exit with a non-zero exit status. 2743If the shell is not an interactive shell, the execution of the shell 2744file will be aborted. 2745Otherwise the shell will return the exit status of the last command 2746executed, or if the 2747.Ic exit 2748builtin is used with a numeric argument, it 2749will return the argument. 2750.Sh SEE ALSO 2751.Xr builtin 1 , 2752.Xr chsh 1 , 2753.Xr echo 1 , 2754.Xr ed 1 , 2755.Xr emacs 1 , 2756.Xr kill 1 , 2757.Xr printf 1 , 2758.Xr pwd 1 , 2759.Xr test 1 , 2760.Xr vi 1 , 2761.Xr execve 2 , 2762.Xr getrlimit 2 , 2763.Xr umask 2 , 2764.Xr wctype 3 , 2765.Xr editrc 5 , 2766.Xr shells 5 2767.Sh HISTORY 2768A 2769.Nm 2770command, the Thompson shell, appeared in 2771.At v1 . 2772It was superseded in 2773.At v7 2774by the Bourne shell, which inherited the name 2775.Nm . 2776.Pp 2777This version of 2778.Nm 2779was rewritten in 1989 under the 2780.Bx 2781license after the Bourne shell from 2782.At V.4 . 2783.Sh AUTHORS 2784This version of 2785.Nm 2786was originally written by 2787.An Kenneth Almquist . 2788.Sh BUGS 2789The 2790.Nm 2791utility does not recognize multibyte characters other than UTF-8. 2792Splitting using 2793.Va IFS 2794and the line editing library 2795.Xr editline 3 2796do not recognize multibyte characters. 2797