1.\" $NetBSD: csh.1,v 1.27 2000/05/21 00:48:45 mason Exp $ 2.\" 3.\" Copyright (c) 1980, 1990, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)csh.1 8.2 (Berkeley) 1/21/94 35.\" 36.Dd July 19, 1998 37.Dt CSH 1 38.Os 39.Sh NAME 40.Nm csh 41.Nd a shell (command interpreter) with C-like syntax 42.Sh SYNOPSIS 43.Nm 44.Op Fl bcefinstvVxX 45.Op arg ... 46.Nm "" 47.Op Fl l 48.Sh DESCRIPTION 49The 50.Nm 51is a command language interpreter 52incorporating a history mechanism (see 53.Sx History Substitutions ) , 54job control facilities (see 55.Sx Jobs ) , 56interactive file name 57and user name completion (see 58.Sx File Name Completion ) , 59and a C-like syntax. It is used both as an interactive 60login shell and a shell script command processor. 61.Ss Argument list processing 62If the first argument (argument 0) to the shell is 63.Ql Fl \& , 64then this is a login shell. 65A login shell also can be specified by invoking the shell with the 66.Ql Fl l 67flag as the only argument. 68.Pp 69The rest of the flag arguments are interpreted as follows: 70.Bl -tag -width 5n 71.It Fl b 72This flag forces a ``break'' from option processing, causing any further 73shell arguments to be treated as non-option arguments. 74The remaining arguments will not be interpreted as shell options. 75This may be used to pass options to a shell script without confusion 76or possible subterfuge. 77The shell will not run a set-user ID script without this option. 78.It Fl c 79Commands are read from the (single) following argument which must 80be present. 81Any remaining arguments are placed in 82.Ar argv . 83.It Fl e 84The shell exits if any invoked command terminates abnormally 85or yields a non-zero exit status. 86.It Fl f 87The shell will start faster, because it will neither search for nor 88execute commands from the file 89.Pa \&.cshrc 90in the invoker's home directory. 91.It Fl i 92The shell is interactive and prompts for its top-level input, 93even if it appears not to be a terminal. 94Shells are interactive without this option if their inputs 95and outputs are terminals. 96.It Fl l 97The shell is a login shell (only applicable if 98.Fl l 99is the only flag specified). 100.It Fl m 101Read 102.Pa \&.cshrc 103even if not owned by the user. This flag is normally given only by 104.Xr su 1 . 105.It Fl n 106Commands are parsed, but not executed. 107This aids in syntactic checking of shell scripts. 108.It Fl s 109Command input is taken from the standard input. 110.It Fl t 111A single line of input is read and executed. 112A 113.Ql \e 114may be used to escape the newline at the end of this 115line and continue onto another line. 116.It Fl v 117Causes the 118.Ar verbose 119variable to be set, with the effect 120that command input is echoed after history substitution. 121.It Fl x 122Causes the 123.Ar echo 124variable to be set, so that commands are echoed immediately before execution. 125.It Fl V 126Causes the 127.Ar verbose 128variable to be set even before 129.Pa .cshrc 130is executed. 131.It Fl X 132Is to 133.Fl x 134as 135.Fl V 136is to 137.Fl v . 138.El 139.Pp 140After processing of flag arguments, if arguments remain but none of the 141.Fl c , 142.Fl i , 143.Fl s , 144or 145.Fl t 146options were given, the first argument is taken as the name of a file of 147commands to be executed. 148The shell opens this file, and saves its name for possible resubstitution 149by `$0'. 150Since many systems use either the standard version 6 or version 7 shells 151whose shell scripts are not compatible with this shell, the shell will 152execute such a `standard' shell if the first character of a script 153is not a `#', i.e., if the script does not start with a comment. 154Remaining arguments initialize the variable 155.Ar argv . 156.Pp 157An instance of 158.Nm 159begins by executing commands from the file 160.Pa /etc/csh.cshrc 161and, 162if this is a login shell, 163.Pa \&/etc/csh.login . 164It then executes 165commands from 166.Pa \&.cshrc 167in the 168.Ar home 169directory of the invoker, and, if this is a login shell, the file 170.Pa \&.login 171in the same location. 172It is typical for users on crt's to put the command ``stty crt'' 173in their 174.Pa \&.login 175file, and to also invoke 176.Xr tset 1 177there. 178.Pp 179In the normal case, the shell will begin reading commands from the 180terminal, prompting with `% '. 181Processing of arguments and the use of the shell to process files 182containing command scripts will be described later. 183.Pp 184The shell repeatedly performs the following actions: 185a line of command input is read and broken into 186.Ar words . 187This sequence of words is placed on the command history list and parsed. 188Finally each command in the current line is executed. 189.Pp 190When a login shell terminates it executes commands from the files 191.Pa .logout 192in the user's 193.Ar home 194directory and 195.Pa /etc/csh.logout . 196.Ss Lexical structure 197The shell splits input lines into words at blanks and tabs with the 198following exceptions. 199The characters 200`&' `\&|' `;' `<' `>' `(' `)' 201form separate words. 202If doubled in `&&', `\&|\&|', `<<' or `>>' these pairs form single words. 203These parser metacharacters may be made part of other words, or prevented their 204special meaning, by preceding them with `\e'. 205A newline preceded by a `\e' is equivalent to a blank. 206.Pp 207Strings enclosed in matched pairs of quotations, 208`'\|', `\*(ga' or `"', 209form parts of a word; metacharacters in these strings, including blanks 210and tabs, do not form separate words. 211These quotations have semantics to be described later. 212Within pairs of `\'' or `"' characters, a newline preceded by a `\e' gives 213a true newline character. 214.Pp 215When the shell's input is not a terminal, 216the character `#' introduces a comment that continues to the end of the 217input line. 218It is prevented this special meaning when preceded by `\e' 219and in quotations using `\`', `\'', and `"'. 220.Ss Commands 221A simple command is a sequence of words, the first of which 222specifies the command to be executed. 223A simple command or 224a sequence of simple commands separated by `\&|' characters 225forms a pipeline. 226The output of each command in a pipeline is connected to the input of the next. 227Sequences of pipelines may be separated by `;', and are then executed 228sequentially. 229A sequence of pipelines may be executed without immediately 230waiting for it to terminate by following it with an `&'. 231.Pp 232Any of the above may be placed in `(' `)' to form a simple command (that 233may be a component of a pipeline, etc.). 234It is also possible to separate pipelines with `\&|\&|' or `&&' showing, 235as in the C language, 236that the second is to be executed only if the first fails or succeeds 237respectively. (See 238.Em Expressions . ) 239.Ss Jobs 240The shell associates a 241.Ar job 242with each pipeline. It keeps 243a table of current jobs, printed by the 244.Ar jobs 245command, and assigns them small integer numbers. When 246a job is started asynchronously with `&', the shell prints a line that looks 247like: 248.Bd -filled -offset indent 249.Op 1 2501234 251.Ed 252.Pp 253showing that the job which was started asynchronously was job number 2541 and had one (top-level) process, whose process id was 1234. 255.Pp 256If you are running a job and wish to do something else you may hit the key 257.Ic ^Z 258(control-Z) which sends a STOP signal to the current job. 259The shell will then normally show that the job has been `Stopped', 260and print another prompt. You can then manipulate the state of this job, 261putting it in the 262.Em background 263with the 264.Ar bg 265command, or run some other 266commands and eventually bring the job back into the foreground with 267the 268.Em foreground 269command 270.Ar fg . 271A 272.Ic ^Z 273takes effect immediately and 274is like an interrupt in that pending output and unread input are discarded 275when it is typed. There is another special key 276.Ic ^Y 277that does not generate a STOP signal until a program attempts to 278.Xr read 2 279it. 280This request can usefully be typed ahead when you have prepared some commands 281for a job that you wish to stop after it has read them. 282.Pp 283A job being run in the background will stop if it tries to read 284from the terminal. Background jobs are normally allowed to produce output, 285but this can be disabled by giving the command ``stty tostop''. 286If you set this 287tty option, then background jobs will stop when they try to produce 288output like they do when they try to read input. 289.Pp 290There are several ways to refer to jobs in the shell. The character 291`%' introduces a job name. If you wish to refer to job number 1, you can 292name it as `%1'. Just naming a job brings it to the foreground; thus 293`%1' is a synonym for `fg %1', bringing job number 1 back into the foreground. 294Similarly saying `%1 &' resumes job number 1 in the background. 295Jobs can also be named by prefixes of the string typed in to start them, 296if these prefixes are unambiguous, thus `%ex' would normally restart 297a suspended 298.Xr ex 1 299job, if there were only one suspended job whose name began with 300the string `ex'. It is also possible to say `%?string' 301which specifies a job whose text contains 302.Ar string , 303if there is only one such job. 304.Pp 305The shell maintains a notion of the current and previous jobs. 306In output about jobs, the current job is marked with a `+' 307and the previous job with a `\-'. The abbreviation `%+' refers 308to the current job and `%\-' refers to the previous job. For close 309analogy with the syntax of the 310.Ar history 311mechanism (described below), 312`%%' is also a synonym for the current job. 313.Pp 314The job control mechanism requires that the 315.Xr stty 1 316option 317.Ic new 318be set. It is an artifact from a 319.Em new 320implementation 321of the 322tty driver that allows generation of interrupt characters from 323the keyboard to tell jobs to stop. See 324.Xr stty 1 325for details on setting options in the new tty driver. 326.Ss Status reporting 327This shell learns immediately whenever a process changes state. 328It normally informs you whenever a job becomes blocked so that 329no further progress is possible, but only just before it prints 330a prompt. This is done so that it does not otherwise disturb your work. 331If, however, you set the shell variable 332.Ar notify , 333the shell will notify you immediately of changes of status in background 334jobs. 335There is also a shell command 336.Ar notify 337that marks a single process so that its status changes will be immediately 338reported. By default 339.Ar notify 340marks the current process; 341simply say `notify' after starting a background job to mark it. 342.Pp 343When you try to leave the shell while jobs are stopped, you will 344be warned that `You have stopped jobs.' You may use the 345.Ar jobs 346command to see what they are. If you do this or immediately try to 347exit again, the shell will not warn you a second time, and the suspended 348jobs will be terminated. 349.Ss File Name Completion 350When the file name completion feature is enabled by setting 351the shell variable 352.Ar filec 353(see 354.Ic set ) , 355.Nm 356will 357interactively complete file names and user names from unique 358prefixes, when they are input from the terminal followed by 359the escape character (the escape key, or control-[) 360For example, 361if the current directory looks like 362.Bd -literal -offset indent 363DSC.OLD bin cmd lib xmpl.c 364DSC.NEW chaosnet cmtest mail xmpl.o 365bench class dev mbox xmpl.out 366.Ed 367.Pp 368and the input is 369.Pp 370.Dl % vi ch<escape> 371.Pp 372.Nm 373will complete the prefix ``ch'' 374to the only matching file name ``chaosnet'', changing the input 375line to 376.Pp 377.Dl % vi chaosnet 378.Pp 379However, given 380.Pp 381.Dl % vi D<escape> 382.Pp 383.Nm 384will only expand the input to 385.Pp 386.Dl % vi DSC. 387.Pp 388and will sound the terminal bell to indicate that the expansion is 389incomplete, since there are two file names matching the prefix ``D''. 390.Pp 391If a partial file name is followed by the end-of-file character 392(usually control-D), then, instead of completing the name, 393.Nm 394will list all file names matching the prefix. For example, 395the input 396.Pp 397.Dl % vi D<control-D> 398.Pp 399causes all files beginning with ``D'' to be listed: 400.Pp 401.Dl DSC.NEW DSC.OLD 402.Pp 403while the input line remains unchanged. 404.Pp 405The same system of escape and end-of-file can also be used to 406expand partial user names, if the word to be completed 407(or listed) begins with the character ``~''. For example, 408typing 409.Pp 410.Dl cd ~ro<escape> 411.Pp 412may produce the expansion 413.Pp 414.Dl cd ~root 415.Pp 416The use of the terminal bell to signal errors or multiple matches 417can be inhibited by setting the variable 418.Ar nobeep . 419.Pp 420Normally, all files in the particular directory are candidates 421for name completion. Files with certain suffixes can be excluded 422from consideration by setting the variable 423.Ar fignore 424to the 425list of suffixes to be ignored. Thus, if 426.Ar fignore 427is set by 428the command 429.Pp 430.Dl % set fignore = (.o .out) 431.Pp 432then typing 433.Pp 434.Dl % vi x<escape> 435.Pp 436would result in the completion to 437.Pp 438.Dl % vi xmpl.c 439.Pp 440ignoring the files "xmpl.o" and "xmpl.out". 441However, if the only completion possible requires not ignoring these 442suffixes, then they are not ignored. In addition, 443.Ar fignore 444does not affect the listing of file names by control-D. All files 445are listed regardless of their suffixes. 446.Ss Substitutions 447We now describe the various transformations the shell performs on the 448input in the order in which they occur. 449.Ss History substitutions 450History substitutions place words from previous command input as portions 451of new commands, making it easy to repeat commands, repeat arguments 452of a previous command in the current command, or fix spelling mistakes 453in the previous command with little typing and a high degree of confidence. 454History substitutions begin with the character `!' and may begin 455.Ar anywhere 456in the input stream (with the proviso that they 457.Em do not 458nest.) 459This `!' may be preceded by a `\e' to prevent its special meaning; for 460convenience, an `!' is passed unchanged when it is followed by a blank, 461tab, newline, `=' or `('. 462(History substitutions also occur when an input line begins with `\*(ua'. 463This special abbreviation will be described later.) 464Any input line that contains history substitution is echoed on the terminal 465before it is executed as it could have been typed without history substitution. 466.Pp 467Commands input from the terminal that consist of one or more words 468are saved on the history list. 469The history substitutions reintroduce sequences of words from these 470saved commands into the input stream. 471The size of the history list is controlled by the 472.Ar history 473variable; the previous command is always retained, 474regardless of the value of the history variable. 475Commands are numbered sequentially from 1. 476.Pp 477For example, consider the following output from the 478.Ar history 479command: 480.Bd -literal -offset indent 481\09 write michael 48210 ex write.c 48311 cat oldwrite.c 48412 diff *write.c 485.Ed 486.Pp 487The commands are shown with their event numbers. 488It is not usually necessary to use event numbers, but the current event 489number can be made part of the 490.Ar prompt 491by placing an `!' in the prompt string. 492.Pp 493With the current event 13 we can refer to previous events by event 494number `!11', relatively as in `!\-2' (referring to the same event), 495by a prefix of a command word 496as in `!d' for event 12 or `!wri' for event 9, or by a string contained in 497a word in the command as in `!?mic?' also referring to event 9. 498These forms, without further change, simply reintroduce the words 499of the specified events, each separated by a single blank. 500As a special case, `!!' refers to the previous command; thus `!!' 501alone is a 502.Ar redo . 503.Pp 504To select words from an event we can follow the event specification by 505a `:' and a designator for the desired words. 506The words of an input line are numbered from 0, 507the first (usually command) word being 0, the second word (first argument) 508being 1, etc. 509The basic word designators are: 510.Pp 511.Bl -tag -width Ds -compact -offset indent 512.It \&0 513first (command) word 514.It Ar n 515.Ar n Ns 'th 516argument 517.It \*(ua 518first argument, i.e., `1' 519.It $ 520last argument 521.It % 522word matched by (immediately preceding) 523.No \&? Ns Ar s Ns \&? 524search 525.It Ar \&x\-y 526range of words 527.It Ar \&\-y 528abbreviates 529.Ar `\&0\-y\' 530.It * 531abbreviates `\*(ua\-$', or nothing if only 1 word in event 532.It Ar x* 533abbreviates 534.Ar `x\-$\' 535.It Ar x\- 536like 537.Ar `x*\' 538but omitting word `$' 539.El 540.Pp 541The `:' separating the event specification from the word designator 542can be omitted if the argument selector begins with a `\*(ua', `$', `*', 543`\-' or `%'. 544After the optional word designator can be 545placed a sequence of modifiers, each preceded by a `:'. 546The following modifiers are defined: 547.Pp 548.Bl -tag -width Ds -compact -offset indent 549.It h 550Remove a trailing pathname component, leaving the head. 551.It r 552Remove a trailing `.xxx' component, leaving the root name. 553.It e 554Remove all but the extension `.xxx' part. 555.It s Ns Ar /l/r/ 556Substitute 557.Ar l 558for 559.Ar r 560.It t 561Remove all leading pathname components, leaving the tail. 562.It \&& 563Repeat the previous substitution. 564.It g 565Apply the change once on each word, prefixing the above, e.g., `g&'. 566.It a 567Apply the change as many times as possible on a single word, prefixing 568the above. It can be used together with `g' to apply a substitution 569globally. 570.It p 571Print the new command line but do not execute it. 572.It q 573Quote the substituted words, preventing further substitutions. 574.It x 575Like q, but break into words at blanks, tabs and newlines. 576.El 577.Pp 578Unless preceded by a `g' the change is applied only to the first 579modifiable word. With substitutions, it is an error for no word to be 580applicable. 581.Pp 582The left hand side of substitutions are not regular expressions in the sense 583of the editors, but instead strings. 584Any character may be used as the delimiter in place of `/'; 585a `\e' quotes the delimiter into the 586.Ar l " " 587and 588.Ar r " " 589strings. 590The character `&' in the right hand side is replaced by the text from 591the left. 592A `\e' also quotes `&'. 593A null 594.Ar l 595(`//') 596uses the previous string either from an 597.Ar l 598or from a 599contextual scan string 600.Ar s 601in 602.No \&`!? Ns Ar s Ns \e?' . 603The trailing delimiter in the substitution may be omitted if a newline 604follows immediately as may the trailing `?' in a contextual scan. 605.Pp 606A history reference may be given without an event specification, e.g., `!$'. 607Here, the reference is to the previous command unless a previous 608history reference occurred on the same line in which case this form repeats 609the previous reference. 610Thus `!?foo?\*(ua !$' gives the first and last arguments 611from the command matching `?foo?'. 612.Pp 613A special abbreviation of a history reference occurs when the first 614non-blank character of an input line is a `\*(ua'. 615This is equivalent to `!:s\*(ua' providing a convenient shorthand for substitutions 616on the text of the previous line. 617Thus `\*(ualb\*(ualib' fixes the spelling of 618`lib' 619in the previous command. 620Finally, a history substitution may be surrounded with `{' and `}' 621if necessary to insulate it from the characters that follow. 622Thus, after `ls \-ld ~paul' we might do `!{l}a' to do `ls \-ld ~paula', 623while `!la' would look for a command starting with `la'. 624.Pp 625.Ss Quotations with \' and \&" 626The quotation of strings by `\'' and `"' can be used 627to prevent all or some of the remaining substitutions. 628Strings enclosed in `\'' are prevented any further interpretation. 629Strings enclosed in `"' may be expanded as described below. 630.Pp 631In both cases the resulting text becomes (all or part of) a single word; 632only in one special case (see 633.Em Command Substitution 634below) does a `"' quoted string yield parts of more than one word; 635`\'' quoted strings never do. 636.Ss Alias substitution 637The shell maintains a list of aliases that can be established, displayed 638and modified by the 639.Ar alias 640and 641.Ar unalias 642commands. 643After a command line is scanned, it is parsed into distinct commands and 644the first word of each command, left-to-right, is checked to see if it 645has an alias. 646If it does, then the text that is the alias for that command is reread 647with the history mechanism available 648as though that command were the previous input line. 649The resulting words replace the 650command and argument list. 651If no reference is made to the history list, then the argument list is 652left unchanged. 653.Pp 654Thus if the alias for `ls' is `ls \-l' the command `ls /usr' would map to 655`ls \-l /usr', the argument list here being undisturbed. 656Similarly if the alias for `lookup' was `grep !\*(ua /etc/passwd' then 657`lookup bill' would map to `grep bill /etc/passwd'. 658.Pp 659If an alias is found, the word transformation of the input text 660is performed and the aliasing process begins again on the reformed input line. 661Looping is prevented if the first word of the new text is the same as the old 662by flagging it to prevent further aliasing. 663Other loops are detected and cause an error. 664.Pp 665Note that the mechanism allows aliases to introduce parser metasyntax. 666Thus, we can `alias print \'pr \e!* \&| lpr\'' to make a command that 667.Ar pr Ns 's 668its arguments to the line printer. 669.Ss Variable substitution 670The shell maintains a set of variables, each of which has as value a list 671of zero or more words. 672Some of these variables are set by the shell or referred to by it. 673For instance, the 674.Ar argv 675variable is an image of the shell's argument list, and words of this 676variable's value are referred to in special ways. 677.Pp 678The values of variables may be displayed and changed by using the 679.Ar set 680and 681.Ar unset 682commands. 683Of the variables referred to by the shell a number are toggles; 684the shell does not care what their value is, 685only whether they are set or not. 686For instance, the 687.Ar verbose 688variable is a toggle that causes command input to be echoed. 689The setting of this variable results from the 690.Fl v 691command line option. 692.Pp 693Other operations treat variables numerically. 694The `@' command permits numeric calculations to be performed and the result 695assigned to a variable. 696Variable values are, however, always represented as (zero or more) strings. 697For the purposes of numeric operations, the null string is considered to be 698zero, and the second and additional words of multiword values are ignored. 699.Pp 700After the input line is aliased and parsed, and before each command 701is executed, variable substitution 702is performed keyed by `$' characters. 703This expansion can be prevented by preceding the `$' with a `\e' except 704within `"'s where it 705.Em always 706occurs, and within `\''s where it 707.Em never 708occurs. 709Strings quoted by `\*(ga' are interpreted later (see 710.Sx Command substitution 711below) so `$' substitution does not occur there until later, if at all. 712A `$' is passed unchanged if followed by a blank, tab, or end-of-line. 713.Pp 714Input/output redirections are recognized before variable expansion, 715and are variable expanded separately. 716Otherwise, the command name and entire argument list are expanded together. 717It is thus possible for the first (command) word (to this point) to generate 718more than one word, the first of which becomes the command name, 719and the rest of which become arguments. 720.Pp 721Unless enclosed in `"' or given the `:q' modifier the results of variable 722substitution may eventually be command and filename substituted. 723Within `"', a variable whose value consists of multiple words expands to a 724(portion of) a single word, with the words of the variables value 725separated by blanks. 726When the `:q' modifier is applied to a substitution 727the variable will expand to multiple words with each word separated 728by a blank and quoted to prevent later command or filename substitution. 729.Pp 730The following metasequences are provided for introducing variable values into 731the shell input. 732Except as noted, it is an error to reference a variable that is not set. 733.Pp 734.Bl -tag -width Ds -compact -offset indent 735.It $name 736.It ${name} 737Are replaced by the words of the value of variable 738.Ar name , 739each separated by a blank. 740Braces insulate 741.Ar name 742from following characters that would otherwise be part of it. 743Shell variables have names consisting of up to 20 letters and digits 744starting with a letter. The underscore character is considered a letter. 745If 746.Ar name 747is not a shell variable, but is set in the environment, then 748that value is returned (but `:' modifiers and the other forms 749given below are not available here). 750.It $name Ns Op selector 751.It ${name Ns [ selector ] Ns } 752May be used to select only some of the words from the value of 753.Ar name . 754The selector is subjected to `$' substitution and may consist of a single 755number or two numbers separated by a `\-'. 756The first word of a variables value is numbered `1'. 757If the first number of a range is omitted it defaults to `1'. 758If the last number of a range is omitted it defaults to `$#name'. 759The selector `*' selects all words. 760It is not an error for a range to be empty if the second argument is omitted 761or in range. 762.It $#name 763.It ${#name} 764Gives the number of words in the variable. 765This is useful for later use in a 766`$argv[selector]'. 767.It $0 768Substitutes the name of the file from which command input is being read. 769An error occurs if the name is not known. 770.It $number 771.It ${number} 772Equivalent to 773`$argv[number]'. 774.It $* 775Equivalent to 776`$argv[*]'. 777.El 778.Pp 779The modifiers `:e', `:h', `:t', `:r', `:q' and `:x' may be applied to 780the substitutions above as may `:gh', `:gt' and `:gr'. 781If braces `{' '}' appear in the command form then the modifiers 782must appear within the braces. 783The current implementation allows only one `:' modifier on each `$' expansion. 784.Pp 785The following substitutions may not be modified with `:' modifiers. 786.Bl -tag -width Ds -compact -offset indent 787.It $?name 788.It ${?name} 789Substitutes the string `1' if name is set, `0' if it is not. 790.It $?0 791Substitutes `1' if the current input filename is known, `0' if it is not. 792.It \&$\&$\& 793Substitute the (decimal) process number of the (parent) shell. 794.It $! 795Substitute the (decimal) process number of the last background process 796started by this shell. 797.It $< 798Substitutes a line from the standard 799input, with no further interpretation. 800It can be used to read from the keyboard in a shell script. 801.El 802.Ss Command and filename substitution 803The remaining substitutions, command and filename substitution, 804are applied selectively to the arguments of builtin commands. 805By selectively, we mean that portions of expressions which are 806not evaluated are not subjected to these expansions. 807For commands that are not internal to the shell, the command 808name is substituted separately from the argument list. 809This occurs very late, 810after input-output redirection is performed, and in a child 811of the main shell. 812.Ss Command substitution 813Command substitution is shown by a command enclosed in `\*(ga'. 814The output from such a command is normally broken into separate words 815at blanks, tabs and newlines, with null words being discarded; 816this text then replaces the original string. 817Within `"'s, only newlines force new words; blanks and tabs are preserved. 818.Pp 819In any case, the single final newline does not force a new word. 820Note that it is thus possible for a command substitution to yield 821only part of a word, even if the command outputs a complete line. 822.Ss Filename substitution 823If a word contains any of the characters `*', `?', `[' or `{' 824or begins with the character `~', then that word is a candidate for 825filename substitution, also known as `globbing'. 826This word is then regarded as a pattern, and replaced with an alphabetically 827sorted list of file names that match the pattern. 828In a list of words specifying filename substitution it is an error for 829no pattern to match an existing file name, but it is not required 830for each pattern to match. 831Only the metacharacters `*', `?' and `[' imply pattern matching, 832the characters `~' and `{' being more akin to abbreviations. 833.Pp 834In matching filenames, the character `.' at the beginning of a filename 835or immediately following a `/', as well as the character `/' must 836be matched explicitly. 837The character `*' matches any string of characters, including the null 838string. 839The character `?' matches any single character. 840The sequence 841.Sq Op ... 842matches any one of the characters enclosed. 843Within 844.Sq Op ... , 845a pair of characters separated by `\-' matches any character lexically between 846the two (inclusive). 847.Pp 848The character `~' at the beginning of a filename refers to home 849directories. 850Standing alone, i.e., `~' it expands to the invokers home directory as reflected 851in the value of the variable 852.Ar home . 853When followed by a name consisting of letters, digits and `\-' characters, 854the shell searches for a user with that name and substitutes their 855home directory; thus `~ken' might expand to `/usr/ken' and `~ken/chmach' 856to `/usr/ken/chmach'. 857If the character `~' is followed by a character other than a letter or `/' 858or does not appear at the beginning of a word, 859it is left undisturbed. 860.Pp 861The metanotation `a{b,c,d}e' is a shorthand for `abe ace ade'. 862Left to right order is preserved, with results of matches being sorted 863separately at a low level to preserve this order. 864This construct may be nested. 865Thus, `~source/s1/{oldls,ls}.c' expands to 866`/usr/source/s1/oldls.c /usr/source/s1/ls.c' 867without chance of error 868if the home directory for `source' is `/usr/source'. 869Similarly `../{memo,*box}' might expand to `../memo ../box ../mbox'. 870(Note that `memo' was not sorted with the results of the match to `*box'.) 871As a special case `{', `}' and `{}' are passed undisturbed. 872.Ss Input/output 873The standard input and the standard output of a command may be redirected 874with the following syntax: 875.Pp 876.Bl -tag -width Ds -compact -offset indent 877.It < name 878Open file 879.Ar name 880(which is first variable, command and filename expanded) as the standard 881input. 882.It << word 883Read the shell input up to a line that is identical to 884.Ar word . 885.Ar Word 886is not subjected to variable, filename or command substitution, 887and each input line is compared to 888.Ar word 889before any substitutions are done on the input line. 890Unless a quoting `\e', `"', `\*(aa' or `\*(ga' appears in 891.Ar word , 892variable and command substitution is performed on the intervening lines, 893allowing `\e' to quote `$', `\e' and `\*(ga'. 894Commands that are substituted have all blanks, tabs, and newlines 895preserved, except for the final newline which is dropped. 896The resultant text is placed in an anonymous temporary file that 897is given to the command as its standard input. 898.It > name 899.It >! name 900.It >& name 901.It >&! name 902The file 903.Ar name 904is used as the standard output. 905If the file does not exist then it is created; 906if the file exists, it is truncated; its previous contents are lost. 907.Pp 908If the variable 909.Ar noclobber 910is set, then the file must not exist or be a character special file (e.g., a 911terminal or `/dev/null') or an error results. 912This helps prevent accidental destruction of files. 913Here, the `!' forms can be used to suppress this check. 914.Pp 915The forms involving `&' route the standard error output into the specified 916file as well as the standard output. 917.Ar Name 918is expanded in the same way as `<' input filenames are. 919.It >> name 920.It >>& name 921.It >>! name 922.It >>&! name 923Uses file 924.Ar name 925as the standard output; 926like `>' but places output at the end of the file. 927If the variable 928.Ar noclobber 929is set, then it is an error for the file not to exist unless 930one of the `!' forms is given. 931Otherwise similar to `>'. 932.El 933.Pp 934A command receives the environment in which the shell was 935invoked as modified by the input-output parameters and 936the presence of the command in a pipeline. 937Thus, unlike some previous shells, commands run from a file of shell commands 938have no access to the text of the commands by default; 939instead they receive the original standard input of the shell. 940The `<<' mechanism should be used to present inline data. 941This permits shell command scripts to function as components of pipelines 942and allows the shell to block read its input. 943Note that the default standard input for a command run detached is 944.Ar not 945modified to be the empty file 946.Pa /dev/null ; 947instead the standard input 948remains as the original standard input of the shell. If this is a terminal 949and if the process attempts to read from the terminal, then the process 950will block and the user will be notified (see 951.Sx Jobs 952above). 953.Pp 954The standard error output may be directed through 955a pipe with the standard output. 956Simply use the form `\&|&' instead of just `\&|'. 957.Ss Expressions 958Several of the builtin commands (to be described later) 959take expressions, in which the operators are similar to those of C, with 960the same precedence, but with the 961.Em opposite grouping: 962right to left. 963These expressions appear in the 964.Ar @ , 965.Ar exit , 966.Ar if , 967and 968.Ar while 969commands. 970The following operators are available: 971.Bd -ragged -offset indent 972\&|\&| && \&| \*(ua & == != =~ !~ <= >= 973< > << >> + \- * / % ! ~ ( ) 974.Ed 975.Pp 976Here the precedence increases to the right, 977`==' `!=' `=~' and `!~', `<=' `>=' `<' and `>', `<<' and `>>', `+' and `\-', 978`*' `/' and `%' being, in groups, at the same level. 979The `==' `!=' `=~' and `!~' operators compare their arguments as strings; 980all others operate on numbers. 981The operators `=~' and `!~' are like `!=' and `==' except that the right 982hand side is a 983.Ar pattern 984(containing, e.g., `*'s, `?'s and instances of `[...]') 985against which the left hand operand is matched. This reduces the 986need for use of the 987.Ar switch 988statement in shell scripts when all that is really needed is pattern matching. 989.Pp 990Strings that begin with `0' are considered octal numbers. 991Null or missing arguments are considered `0'. 992The result of all expressions are strings, 993which represent decimal numbers. 994It is important to note that no two components of an expression can appear 995in the same word; except when adjacent to components of expressions that 996are syntactically significant to the parser (`&' `\&|' `<' `>' `(' `)'), 997they should be surrounded by spaces. 998.Pp 999Also available in expressions as primitive operands are command executions 1000enclosed in `{' and `}' 1001and file enquiries of the form 1002.Fl l 1003.Ar name 1004where 1005.Ic l 1006is one of: 1007.Bd -literal -offset indent 1008r read access 1009w write access 1010x execute access 1011e existence 1012o ownership 1013z zero size 1014f plain file 1015d directory 1016.Ed 1017.Pp 1018The specified name is command and filename expanded and then tested 1019to see if it has the specified relationship to the real user. 1020If the file does not exist or is inaccessible then all enquiries return 1021false, i.e., `0'. 1022Command executions succeed, returning true, i.e., `1', 1023if the command exits with status 0, otherwise they fail, returning 1024false, i.e., `0'. 1025If more detailed status information is required then the command 1026should be executed outside an expression and the variable 1027.Ar status 1028examined. 1029.Ss Control flow 1030The shell contains several commands that can be used to regulate the 1031flow of control in command files (shell scripts) and 1032(in limited but useful ways) from terminal input. 1033These commands all operate by forcing the shell to reread or skip in its 1034input and, because of the implementation, restrict the placement of some 1035of the commands. 1036.Pp 1037The 1038.Ic foreach , 1039.Ic switch , 1040and 1041.Ic while 1042statements, as well as the 1043.Ic if\-then\-else 1044form of the 1045.Ic if 1046statement require that the major keywords appear in a single simple command 1047on an input line as shown below. 1048.Pp 1049If the shell's input is not seekable, 1050the shell buffers up input whenever a loop is being read 1051and performs seeks in this internal buffer to accomplish the rereading 1052implied by the loop. 1053(To the extent that this allows, backward goto's will succeed on 1054non-seekable inputs.) 1055.Ss Builtin commands 1056Builtin commands are executed within the shell. 1057If a builtin command occurs as any component of a pipeline 1058except the last then it is executed in a subshell. 1059.Pp 1060.Bl -tag -width Ds -compact -offset indent 1061.It Ic alias 1062.It Ic alias Ar name 1063.It Ic alias Ar name wordlist 1064The first form prints all aliases. 1065The second form prints the alias for name. 1066The final form assigns the specified 1067.Ar wordlist 1068as the alias of 1069.Ar name ; 1070.Ar wordlist 1071is command and filename substituted. 1072.Ar Name 1073is not allowed to be 1074.Ar alias 1075or 1076.Ar unalias . 1077.Pp 1078.It Ic alloc 1079Shows the amount of dynamic memory acquired, broken down into used and 1080free memory. 1081With an argument shows the number of free and used blocks in each size 1082category. The categories start at size 8 and double at each step. 1083This command's output may vary across system types, since 1084systems other than the VAX may use a different memory allocator. 1085.Pp 1086.It Ic bg 1087.It Ic bg \&% Ns Ar job ... 1088Puts the current or specified jobs into the background, continuing them 1089if they were stopped. 1090.Pp 1091.It Ic break 1092Causes execution to resume after the 1093.Ic end 1094of the nearest enclosing 1095.Ic foreach 1096or 1097.Ic while . 1098The remaining commands on the current line are executed. 1099Multi-level breaks are thus possible by writing them all on one line. 1100.Pp 1101.It Ic breaksw 1102Causes a break from a 1103.Ic switch , 1104resuming after the 1105.Ic endsw . 1106.Pp 1107.It Ic case Ar label : 1108A label in a 1109.Ic switch 1110statement as discussed below. 1111.Pp 1112.It Ic cd 1113.It Ic cd Ar name 1114.It Ic chdir 1115.It Ic chdir Ar name 1116Change the shell's working directory to directory 1117.Ar name . 1118If no argument is given then change to the home directory of the user. 1119If 1120.Ar name 1121is not found as a subdirectory of the current directory (and does not begin 1122with `/', `./' or `../'), then each 1123component of the variable 1124.Ic cdpath 1125is checked to see if it has a subdirectory 1126.Ar name . 1127Finally, if all else fails but 1128.Ar name 1129is a shell variable whose value begins with `/', then this 1130is tried to see if it is a directory. 1131.Pp 1132.It Ic continue 1133Continue execution of the nearest enclosing 1134.Ic while 1135or 1136.Ic foreach . 1137The rest of the commands on the current line are executed. 1138.Pp 1139.It Ic default : 1140Labels the default case in a 1141.Ic switch 1142statement. 1143The default should come after all 1144.Ic case 1145labels. 1146.Pp 1147.It Ic dirs 1148Prints the directory stack; the top of the stack is at the left, 1149the first directory in the stack being the current directory. 1150.Pp 1151.It Ic echo Ar wordlist 1152.It Ic echo Fl n Ar wordlist 1153The specified words are written to the shell's standard output, separated 1154by spaces, and terminated with a newline unless the 1155.Fl n 1156option is specified. 1157.Pp 1158.It Ic else 1159.It Ic end 1160.It Ic endif 1161.It Ic endsw 1162See the description of the 1163.Ic foreach , 1164.Ic if , 1165.Ic switch , 1166and 1167.Ic while 1168statements below. 1169.Pp 1170.It Ic eval Ar arg ... 1171(As in 1172.Xr sh 1 . ) 1173The arguments are read as input to the shell and the resulting 1174command(s) executed in the context of the current shell. 1175This is usually used to execute commands 1176generated as the result of command or variable substitution, since 1177parsing occurs before these substitutions. See 1178.Xr tset 1 1179for an example of using 1180.Ic eval . 1181.Pp 1182.It Ic exec Ar command 1183The specified command is executed in place of the current shell. 1184.Pp 1185.It Ic exit 1186.It Ic exit Ar ( expr ) 1187The shell exits either with the value of the 1188.Ic status 1189variable (first form) or with the value of the specified 1190.Ic expr 1191(second form). 1192.Pp 1193.It Ic fg 1194.It Ic fg % Ns Ar job ... 1195Brings the current or specified jobs into the foreground, continuing them if 1196they were stopped. 1197.Pp 1198.It Ic foreach Ar name ( wordlist ) 1199.It ... 1200.It Ic end 1201The variable 1202.Ic name 1203is successively set to each member of 1204.Ic wordlist 1205and the sequence of commands between this command and the matching 1206.Ic end 1207are executed. 1208(Both 1209.Ic foreach 1210and 1211.Ic end 1212must appear alone on separate lines.) 1213The builtin command 1214.Ic continue 1215may be used to continue the loop prematurely and the builtin 1216command 1217.Ic break 1218to terminate it prematurely. 1219When this command is read from the terminal, the loop is read once 1220prompting with `?' before any statements in the loop are executed. 1221If you make a mistake typing in a loop at the terminal you can rub it out. 1222.Pp 1223.It Ic glob Ar wordlist 1224Like 1225.Ic echo 1226but no `\e' escapes are recognized and words are delimited 1227by null characters in the output. 1228Useful for programs that wish to use the shell to filename expand a list 1229of words. 1230.Pp 1231.It Ic goto Ar word 1232The specified 1233.Ic word 1234is filename and command expanded to yield a string of the form `label'. 1235The shell rewinds its input as much as possible 1236and searches for a line of the form `label:' 1237possibly preceded by blanks or tabs. 1238Execution continues after the specified line. 1239.Pp 1240.It Ic hashstat 1241Print a statistics line showing how effective the internal hash 1242table has been at locating commands (and avoiding 1243.Ic exec Ns \'s ) . 1244An 1245.Ic exec 1246is attempted for each component of the 1247.Em path 1248where the hash function indicates a possible hit, and in each component 1249that does not begin with a `/'. 1250.Pp 1251.It Ic history 1252.It Ic history Ar n 1253.It Ic history Fl r Ar n 1254.It Ic history Fl h Ar n 1255Displays the history event list; if 1256.Ar n 1257is given only the 1258.Ar n 1259most recent events are printed. 1260The 1261.Fl r 1262option reverses the order of printout to be most recent first 1263instead of oldest first. 1264The 1265.Fl h 1266option causes the history list to be printed without leading numbers. 1267This format produces files suitable for sourcing using the \-h 1268option to 1269.Ic source . 1270.Pp 1271.It Ic if Ar ( expr ) No command 1272If the specified expression evaluates true, then the single 1273.Ar command 1274with arguments is executed. 1275Variable substitution on 1276.Ar command 1277happens early, at the same 1278time it does for the rest of the 1279.Ic if 1280command. 1281.Ar Command 1282must be a simple command, not 1283a pipeline, a command list, or a parenthesized command list. 1284Input/output redirection occurs even if 1285.Ar expr 1286is false, i.e., when command is 1287.Em not 1288executed (this is a bug). 1289.Pp 1290.It Ic if Ar ( expr ) Ic then 1291.It ... 1292.It Ic else if Ar ( expr2 ) Ic then 1293.It ... 1294.It Ic else 1295.It ... 1296.It Ic endif 1297If the specified 1298.Ar expr 1299is true then the commands up to the first 1300.Ic else 1301are executed; otherwise if 1302.Ar expr2 1303is true then the commands up to the 1304second 1305.Ic else 1306are executed, etc. 1307Any number of 1308.Ic else-if 1309pairs are possible; only one 1310.Ic endif 1311is needed. 1312The 1313.Ic else 1314part is likewise optional. 1315(The words 1316.Ic else 1317and 1318.Ic endif 1319must appear at the beginning of input lines; 1320the 1321.Ic if 1322must appear alone on its input line or after an 1323.Ic else . ) 1324.Pp 1325.It Ic jobs 1326.It Ic jobs Fl l 1327Lists the active jobs; the 1328.Fl l 1329option lists process id's in addition to the normal information. 1330.Pp 1331.It Ic kill % Ns Ar job 1332.It Ic kill Ar pid ... 1333.It Ic kill Fl l Op Ar exit_status 1334.It Ic kill Fl s Ar signal_name pid ... 1335.It Ic kill Fl Ar signal_name Ar pid ... 1336.It Ic kill Fl Ar signal_number Ar pid ... 1337Sends either the TERM (terminate) signal or the 1338specified signal to the specified jobs or processes. 1339Signals are either given by number or by names (as given in 1340.Aq Pa signal.h , 1341stripped of the prefix ``SIG''). 1342The signal names are listed by ``kill \-l''; 1343if an 1344.Ar exit_status 1345is specified, only the corresponding signal name will be written. 1346There is no default, just saying `kill' does not 1347send a signal to the current job. 1348If the signal being sent is TERM (terminate) or HUP (hangup), 1349then the job or process will be sent a CONT (continue) signal as well. 1350.Pp 1351.It Ic limit 1352.It Ic limit Ar resource 1353.It Ic limit Ar resource maximum-use 1354.It Ic limit Fl h 1355.It Ic limit Fl h Ar resource 1356.It Ic limit Fl h Ar resource maximum-use 1357Limits the consumption by the current process and each process 1358it creates to not individually exceed 1359.Ar maximum-use 1360on the 1361specified 1362.Ar resource . 1363If no 1364.Ar maximum-use 1365is given, then 1366the current limit is printed; if no 1367.Ar resource 1368is given, then 1369all limitations are given. If the 1370.Fl h 1371flag is given, the hard limits are used instead of the current 1372limits. The hard limits impose a ceiling on the values of 1373the current limits. Only the super-user may raise the hard limits, 1374but a user may lower or raise the current limits within the legal range. 1375.Pp 1376Resources controllable currently include 1377.Ar cputime 1378(the maximum 1379number of cpu-seconds to be used by each process), 1380.Ar filesize 1381(the largest single file that can be created), 1382.Ar datasize 1383(the maximum growth of the data+stack region via 1384.Xr sbrk 2 1385beyond the end of the program text), 1386.Ar stacksize 1387(the maximum 1388size of the automatically-extended stack region), and 1389.Ar coredumpsize 1390(the size of the largest core dump that will be created). 1391.Pp 1392The 1393.Ar maximum-use 1394may be given as a (floating point or integer) 1395number followed by a scale factor. For all limits other than 1396.Ar cputime 1397the default scale is `k' or `kilobytes' (1024 bytes); 1398a scale factor of `m' or `megabytes' may also be used. 1399For 1400.Ar cputime 1401the default scale is `seconds'; 1402a scale factor of `m' for minutes 1403or `h' for hours, or a time of the form `mm:ss' giving minutes 1404and seconds also may be used. 1405.Pp 1406For both 1407.Ar resource 1408names and scale factors, unambiguous prefixes 1409of the names suffice. 1410.Pp 1411Limits of an arbitrary process can be displayed or set using the 1412.Xr sysctl(8) 1413utility. 1414.Pp 1415.It Ic login 1416Terminate a login shell, replacing it with an instance of 1417.Pa /usr/bin/login. 1418This is one way to log off, included for compatibility with 1419.Xr sh 1 . 1420.Pp 1421.It Ic logout 1422Terminate a login shell. 1423Especially useful if 1424.Ic ignoreeof 1425is set. 1426.Pp 1427.It Ic nice 1428.It Ic nice Ar +number 1429.It Ic nice Ar command 1430.It Ic nice Ar +number command 1431The first form sets the 1432scheduling priority 1433for this shell to 4. 1434The second form sets the 1435priority 1436to the given 1437.Ar number . 1438The final two forms run command at priority 4 and 1439.Ar number 1440respectively. 1441The greater the number, the less cpu the process will get. 1442The super-user may specify negative priority by using `nice \-number ...'. 1443.Ar Command 1444is always executed in a sub-shell, and the restrictions 1445placed on commands in simple 1446.Ic if 1447statements apply. 1448.Pp 1449.It Ic nohup 1450.It Ic nohup Ar command 1451The first form can be used in shell scripts to cause hangups to be 1452ignored for the remainder of the script. 1453The second form causes the specified command to be run with hangups 1454ignored. 1455All processes detached with `&' are effectively 1456.Ic nohup Ns \'ed . 1457.Pp 1458.It Ic notify 1459.It Ic notify % Ns Ar job ... 1460Causes the shell to notify the user asynchronously when the status of the 1461current or specified jobs change; normally notification is presented 1462before a prompt. This is automatic if the shell variable 1463.Ic notify 1464is set. 1465.Pp 1466.It Ic onintr 1467.It Ic onintr Fl 1468.It Ic onintr Ar label 1469Control the action of the shell on interrupts. 1470The first form restores the default action of the shell on interrupts 1471which is to terminate shell scripts or to return to the terminal command 1472input level. 1473The second form `onintr \-' causes all interrupts to be ignored. 1474The final form causes the shell to execute a `goto label' when 1475an interrupt is received or a child process terminates because 1476it was interrupted. 1477.Pp 1478In any case, if the shell is running detached and interrupts are 1479being ignored, all forms of 1480.Ic onintr 1481have no meaning and interrupts 1482continue to be ignored by the shell and all invoked commands. 1483Finally 1484.Ic onintr 1485statements are ignored in the system startup files where interrupts 1486are disabled (/etc/csh.cshrc, /etc/csh.login). 1487.Pp 1488.It Ic popd 1489.It Ic popd Ar +n 1490Pops the directory stack, returning to the new top directory. 1491With an argument 1492.Ns \`+ Ar n Ns \' 1493discards the 1494.Ar n Ns \'th 1495entry in the stack. 1496The members of the directory stack are numbered from the top starting at 0. 1497.Pp 1498.It Ic pushd 1499.It Ic pushd Ar name 1500.It Ic pushd Ar n 1501With no arguments, 1502.Ic pushd 1503exchanges the top two elements of the directory stack. 1504Given a 1505.Ar name 1506argument, 1507.Ic pushd 1508changes to the new directory (ala 1509.Ic cd ) 1510and pushes the old current working directory 1511(as in 1512.Ic cwd ) 1513onto the directory stack. 1514With a numeric argument, 1515.Ic pushd 1516rotates the 1517.Ar n Ns \'th 1518argument of the directory 1519stack around to be the top element and changes to it. The members 1520of the directory stack are numbered from the top starting at 0. 1521.Pp 1522.It Ic rehash 1523Causes the internal hash table of the contents of the directories in 1524the 1525.Ic path 1526variable to be recomputed. This is needed if new commands are added 1527to directories in the 1528.Ic path 1529while you are logged in. This should only be necessary if you add 1530commands to one of your own directories, or if a systems programmer 1531changes the contents of a system directory. 1532.Pp 1533.It Ic repeat Ar count command 1534The specified 1535.Ar command 1536which is subject to the same restrictions 1537as the 1538.Ar command 1539in the one line 1540.Ic if 1541statement above, 1542is executed 1543.Ar count 1544times. 1545I/O redirections occur exactly once, even if 1546.Ar count 1547is 0. 1548.Pp 1549.It Ic set 1550.It Ic set Ar name 1551.It Ic set Ar name Ns =word 1552.It Ic set Ar name[index] Ns =word 1553.It Ic set Ar name Ns =(wordlist) 1554The first form of the command shows the value of all shell variables. 1555Variables that have other than a single word as their 1556value print as a parenthesized word list. 1557The second form sets 1558.Ar name 1559to the null string. 1560The third form sets 1561.Ar name 1562to the single 1563.Ar word . 1564The fourth form sets 1565the 1566.Ar index Ns 'th 1567component of 1568.Ar name 1569to 1570.Ar word ; 1571this component must already exist. 1572The final form sets 1573.Ar name 1574to the list of words in 1575.Ar wordlist . 1576The value is always command and filename expanded. 1577.Pp 1578These arguments may be repeated to set multiple values in a single set command. 1579Note however, that variable expansion happens for all arguments before any 1580setting occurs. 1581.Pp 1582.It Ic setenv 1583.It Ic setenv Ar name 1584.It Ic setenv Ar name value 1585The first form lists all current environment variables. 1586It is equivalent to 1587.Xr printenv 1 . 1588The last form sets the value of environment variable 1589.Ar name 1590to be 1591.Ar value , 1592a single string. The second form sets 1593.Ar name 1594to an empty string. 1595The most commonly used environment variables 1596.Ev USER , 1597.Ev TERM , 1598and 1599.Ev PATH 1600are automatically imported to and exported from the 1601.Nm 1602variables 1603.Ar user , 1604.Ar term , 1605and 1606.Ar path ; 1607there is no need to use 1608.Ic setenv 1609for these. 1610.Pp 1611.It Ic shift 1612.It Ic shift Ar variable 1613The members of 1614.Ic argv 1615are shifted to the left, discarding 1616.Ic argv Ns Bq 1 . 1617It is an error for 1618.Ic argv 1619not to be set or to have less than one word as value. 1620The second form performs the same function on the specified variable. 1621.Pp 1622.It Ic source Ar name 1623.It Ic source Fl h Ar name 1624The shell reads commands from 1625.Ar name . 1626.Ic Source 1627commands may be nested; if they are nested too deeply the shell may 1628run out of file descriptors. 1629An error in a 1630.Ic source 1631at any level terminates all nested 1632.Ic source 1633commands. 1634Normally input during 1635.Ic source 1636commands is not placed on the history list; 1637the \-h option causes the commands to be placed on the 1638history list without being executed. 1639.Pp 1640.It Ic stop 1641.It Ic stop % Ns Ar job ... 1642Stops the current or specified jobs that are executing in the background. 1643.Pp 1644.It Ic suspend 1645Causes the shell to stop in its tracks, much as if it had been sent a stop 1646signal with 1647.Ic ^Z . 1648This is most often used to stop shells started by 1649.Xr su 1 . 1650.Pp 1651.It Ic switch Ar ( string ) 1652.It Ic case Ar str1 : 1653.It \ \ \ \ \&... 1654.It Ic \ \ \ \ breaksw 1655.It \ \ \ \ \&... 1656.It Ic default : 1657.It \ \ \ \ \&... 1658.It Ic \ \ \ \ breaksw 1659.It Ic endsw 1660Each case label is successively matched against the specified 1661.Ar string 1662which is first command and filename expanded. 1663The file metacharacters `*', `?' and `[...]' 1664may be used in the case labels, 1665which are variable expanded. 1666If none of the labels match before the `default' label is found, then 1667the execution begins after the default label. 1668Each case label and the default label must appear at the beginning of a line. 1669The command 1670.Ic breaksw 1671causes execution to continue after the 1672.Ic endsw . 1673Otherwise control may fall through case labels and the default label as in C. 1674If no label matches and there is no default, execution continues after 1675the 1676.Ic endsw . 1677.Pp 1678.It Ic time 1679.It Ic time Ar command 1680With no argument, a summary of time used by this shell and its children 1681is printed. 1682If arguments are given 1683the specified simple command is timed and a time summary 1684as described under the 1685.Ic time 1686variable is printed. If necessary, an extra shell is created to print the time 1687statistic when the command completes. 1688.Pp 1689.It Ic umask 1690.It Ic umask Ar value 1691The file creation mask is displayed (first form) or set to the specified 1692value (second form). The mask is given in octal. Common values for 1693the mask are 002 giving all access to the group and read and execute 1694access to others or 022 giving all access except write access for 1695users in the group or others. 1696.Pp 1697.It Ic unalias Ar pattern 1698All aliases whose names match the specified pattern are discarded. 1699Thus all aliases are removed by `unalias *'. 1700It is not an error for nothing to be 1701.Ic unaliased . 1702.Pp 1703.It Ic unhash 1704Use of the internal hash table to speed location of executed programs 1705is disabled. 1706.Pp 1707.It Ic unlimit 1708.It Ic unlimit Ar resource 1709.It Ic unlimit Fl h 1710.It Ic unlimit Fl h Ar resource 1711Removes the limitation on 1712.Ar resource . 1713If no 1714.Ar resource 1715is specified, then all 1716.Ar resource 1717limitations are removed. If 1718.Fl h 1719is given, the corresponding hard limits are removed. Only the 1720super-user may do this. 1721.Pp 1722.It Ic unset Ar pattern 1723All variables whose names match the specified pattern are removed. 1724Thus all variables are removed by `unset *'; this has noticeably 1725distasteful side-effects. 1726It is not an error for nothing to be 1727.Ic unset . 1728.Pp 1729.It Ic unsetenv Ar pattern 1730Removes all variables whose name match the specified pattern from the 1731environment. See also the 1732.Ic setenv 1733command above and 1734.Xr printenv 1 . 1735.Pp 1736.It Ic wait 1737Wait for all background jobs. 1738If the shell is interactive, then an interrupt can disrupt the wait. 1739After the interrupt, the shell prints names and job numbers of all jobs 1740known to be outstanding. 1741.Pp 1742.It Ic which Ar command 1743Displays the resolved command that will be executed by the shell. 1744.Pp 1745.It Ic while Ar ( expr ) 1746.It \&... 1747.It Ic end 1748While the specified expression evaluates non-zero, the commands between 1749the 1750.Ic while 1751and the matching 1752.Ic end 1753are evaluated. 1754.Ic Break 1755and 1756.Ic continue 1757may be used to terminate or continue the loop prematurely. 1758(The 1759.Ic while 1760and 1761.Ic end 1762must appear alone on their input lines.) 1763Prompting occurs here the first time through the loop as for the 1764.Ic foreach 1765statement if the input is a terminal. 1766.Pp 1767.It Ic % Ns Ar job 1768Brings the specified job into the foreground. 1769.Pp 1770.It Ic % Ns Ar job Ic & 1771Continues the specified job in the background. 1772.Pp 1773.It Ic @ 1774.It Ic @ Ar name Ns = expr 1775.It Ic @ Ar name[index] Ns = expr 1776The first form prints the values of all the shell variables. 1777The second form sets the specified 1778.Ar name 1779to the value of 1780.Ar expr . 1781If the expression contains `<', `>', `&' or `|' then at least 1782this part of the expression must be placed within `(' `)'. 1783The third form assigns the value of 1784.Ar expr 1785to the 1786.Ar index Ns 'th 1787argument of 1788.Ar name . 1789Both 1790.Ar name 1791and its 1792.Ar index Ns 'th 1793component must already exist. 1794.El 1795.Pp 1796The operators `*=', `+=', etc are available as in C. 1797The space separating the name from the assignment operator is optional. 1798Spaces are, however, mandatory in separating components of 1799.Ar expr 1800which would otherwise be single words. 1801.Pp 1802Special postfix `+\|+' and `\-\|\-' operators increment and decrement 1803.Ar name 1804respectively, i.e., `@ i++'. 1805.Ss Pre-defined and environment variables 1806The following variables have special meaning to the shell. 1807Of these, 1808.Ar argv , 1809.Ar cwd , 1810.Ar home , 1811.Ar path , 1812.Ar prompt , 1813.Ar shell 1814and 1815.Ar status 1816are always set by the shell. 1817Except for 1818.Ar cwd 1819and 1820.Ar status , 1821this setting occurs only at initialization; 1822these variables will not then be modified unless done 1823explicitly by the user. 1824.Pp 1825The shell copies the environment variable 1826.Ev USER 1827into the variable 1828.Ar user , 1829.Ev TERM 1830into 1831.Ar term , 1832and 1833.Ev HOME 1834into 1835.Ar home , 1836and copies these back into the environment whenever the normal 1837shell variables are reset. 1838The environment variable 1839.Ev PATH 1840is likewise handled; it is not 1841necessary to worry about its setting other than in the file 1842.Ar \&.cshrc 1843as inferior 1844.Nm 1845processes will import the definition of 1846.Ar path 1847from the environment, and re-export it if you then change it. 1848.Bl -tag -width histchars 1849.It Ic argv 1850Set to the arguments to the shell, it is from this variable that 1851positional parameters are substituted, i.e., `$1' is replaced by 1852`$argv[1]', 1853etc. 1854.It Ic cdpath 1855Gives a list of alternative directories searched to find subdirectories 1856in 1857.Ar chdir 1858commands. 1859.It Ic cwd 1860The full pathname of the current directory. 1861.It Ic echo 1862Set when the 1863.Fl x 1864command line option is given. 1865Causes each command and its arguments 1866to be echoed just before it is executed. 1867For non-builtin commands all expansions occur before echoing. 1868Builtin commands are echoed before command and filename substitution, 1869since these substitutions are then done selectively. 1870.It Ic filec 1871Enable file name completion. 1872.It Ic histchars 1873Can be given a string value to change the characters used in history 1874substitution. The first character of its value is used as the 1875history substitution character, replacing the default character `!'. 1876The second character of its value replaces the character `\(ua' in 1877quick substitutions. 1878.It Ic histfile 1879Can be set to the pathname where history is going to be saved/restored. 1880.It Ic history 1881Can be given a numeric value to control the size of the history list. 1882Any command that has been referenced in this many events will not be 1883discarded. 1884Too large values of 1885.Ar history 1886may run the shell out of memory. 1887The last executed command is always saved on the history list. 1888.It Ic home 1889The home directory of the invoker, initialized from the environment. 1890The filename expansion of 1891.Sq Pa ~ 1892refers to this variable. 1893.It Ic ignoreeof 1894If set the shell ignores 1895end-of-file from input devices which are terminals. 1896This prevents shells from accidentally being killed by control-D's. 1897.It Ic mail 1898The files where the shell checks for mail. 1899This checking is done after each command completion that will 1900result in a prompt, 1901if a specified interval has elapsed. 1902The shell says `You have new mail.' 1903if the file exists with an access time not greater than its modify time. 1904.Pp 1905If the first word of the value of 1906.Ar mail 1907is numeric it specifies a different mail checking interval, in seconds, 1908than the default, which is 10 minutes. 1909.Pp 1910If multiple mail files are specified, then the shell says 1911`New mail in 1912.Ar name Ns ' 1913when there is mail in the file 1914.Ar name . 1915.It Ic noclobber 1916As described in the section on 1917.Sx input/output , 1918restrictions are placed on output redirection to insure that 1919files are not accidentally destroyed, and that `>>' redirections 1920refer to existing files. 1921.It Ic noglob 1922If set, filename expansion is inhibited. 1923This inhibition is most useful in shell scripts that 1924 are not dealing with filenames, 1925or after a list of filenames has been obtained and further expansions 1926are not desirable. 1927.It Ic nonomatch 1928If set, it is not an error for a filename expansion to not match any 1929existing files; instead the primitive pattern is returned. 1930It is still an error for the primitive pattern to be malformed, i.e., 1931`echo [' 1932still gives an error. 1933.It Ic notify 1934If set, the shell notifies asynchronously of job completions; 1935the default is to present job completions just before printing 1936a prompt. 1937.It Ic path 1938Each word of the path variable specifies a directory in which 1939commands are to be sought for execution. 1940A null word specifies the current directory. 1941If there is no 1942.Ar path 1943variable then only full path names will execute. 1944The usual search path is `.', `/bin' and `/usr/bin', but this 1945may vary from system to system. 1946For the super-user the default search path is `/etc', `/bin' and `/usr/bin'. 1947A shell that is given neither the 1948.Fl c 1949nor the 1950.Fl t 1951option will normally hash the contents of the directories in the 1952.Ar path 1953variable after reading 1954.Ar \&.cshrc , 1955and each time the 1956.Ar path 1957variable is reset. If new commands are added to these directories 1958while the shell is active, it may be necessary to do a 1959.Ic rehash 1960or the commands may not be found. 1961.It Ic prompt 1962The string that is printed before each command is read from 1963an interactive terminal input. 1964If a `!' appears in the string it will be replaced by the current event number 1965unless a preceding `\e' is given. 1966Default is `% ', or `# ' for the super-user. 1967.It Ic savehist 1968Is given a numeric value to control the number of entries of the 1969history list that are saved in ~/.history when the user logs out. 1970Any command that has been referenced in this many events will be saved. 1971During start up the shell sources ~/.history into the history list 1972enabling history to be saved across logins. 1973Too large values of 1974.Ar savehist 1975will slow down the shell during start up. 1976If 1977.Ar savehist 1978is just set, the shell will use the value of 1979.Ar history. 1980.It Ic shell 1981The file in which the shell resides. 1982This variable is used in forking shells to interpret files that have execute 1983bits set, but which are not executable by the system. 1984(See the description of 1985.Sx Non-builtin Command Execution 1986below.) 1987Initialized to the (system-dependent) home of the shell. 1988.It Ic status 1989The status returned by the last command. 1990If it terminated abnormally, then 0200 is added to the status. 1991Builtin commands that fail return exit status `1', 1992all other builtin commands set status to `0'. 1993.It Ic time 1994Controls automatic timing of commands. 1995If set, then any command that takes more than this many cpu seconds 1996will cause a line giving user, system, and real times and a utilization 1997percentage which is the ratio of user plus system times to real time 1998to be printed when it terminates. 1999.It Ic verbose 2000Set by the 2001.Fl v 2002command line option, causes the words of each command to be printed 2003after history substitution. 2004.El 2005.Ss Non-builtin command execution 2006When a command to be executed is found to not be a builtin command 2007the shell attempts to execute the command via 2008.Xr execve 2 . 2009Each word in the variable 2010.Ar path 2011names a directory from which the shell will attempt to execute the command. 2012If it is given neither a 2013.Fl c 2014nor a 2015.Fl t 2016option, the shell will hash the names in these directories into an internal 2017table so that it will only try an 2018.Ic exec 2019in a directory if there is a possibility that the command resides there. 2020This shortcut greatly speeds command location when many directories 2021are present in the search path. 2022If this mechanism has been turned off (via 2023.Ic unhash ) , 2024or if the shell was given a 2025.Fl c 2026or 2027.Fl t 2028argument, and in any case for each directory component of 2029.Ar path 2030that does not begin with a `/', 2031the shell concatenates with the given command name to form a path name 2032of a file which it then attempts to execute. 2033.Pp 2034Parenthesized commands are always executed in a subshell. 2035Thus 2036.Pp 2037.Dl (cd ; pwd) ; pwd 2038.Pp 2039prints the 2040.Ar home 2041directory; leaving you where you were (printing this after the home directory), 2042while 2043.Pp 2044.Dl cd ; pwd 2045.Pp 2046leaves you in the 2047.Ar home 2048directory. 2049Parenthesized commands are most often used to prevent 2050.Ic chdir 2051from affecting the current shell. 2052.Pp 2053If the file has execute permissions but is not an 2054executable binary to the system, then it is assumed to be a 2055file containing shell commands and a new shell is spawned to read it. 2056.Pp 2057If there is an 2058.Ic alias 2059for 2060.Ic shell 2061then the words of the alias will be prepended to the argument list to form 2062the shell command. 2063The first word of the 2064.Ic alias 2065should be the full path name of the shell 2066(e.g., `$shell'). 2067Note that this is a special, late occurring, case of 2068.Ic alias 2069substitution, 2070and only allows words to be prepended to the argument list without change. 2071.Ss Signal handling 2072The shell normally ignores 2073.Ar quit 2074signals. 2075Jobs running detached (either by 2076.Ic \&& 2077or the 2078.Ic bg 2079or 2080.Ic %... & 2081commands) are immune to signals generated from the keyboard, including 2082hangups. 2083Other signals have the values which the shell inherited from its parent. 2084The shell's handling of interrupts and terminate signals 2085in shell scripts can be controlled by 2086.Ic onintr . 2087Login shells catch the 2088.Ar terminate 2089signal; otherwise this signal is passed on to children from the state in the 2090shell's parent. 2091Interrupts are not allowed when a login shell is reading the file 2092.Pa \&.logout . 2093.Sh AUTHOR 2094William Joy. 2095Job control and directory stack features first implemented by J.E. Kulp of 2096IIASA, Laxenburg, Austria, 2097with different syntax than that used now. 2098File name completion code written by Ken Greer, HP Labs. 2099Eight-bit implementation Christos S. Zoulas, Cornell University. 2100.Sh FILES 2101.Bl -tag -width /etc/passwd -compact 2102.It Pa ~/.cshrc 2103Read at beginning of execution by each shell. 2104.It Pa ~/.login 2105Read by login shell, after `.cshrc' at login. 2106.It Pa ~/.logout 2107Read by login shell, at logout. 2108.It Pa /bin/sh 2109Standard shell, for shell scripts not starting with a `#'. 2110.It Pa /tmp/sh* 2111Temporary file for `<<'. 2112.It Pa /etc/passwd 2113Source of home directories for `~name'. 2114.El 2115.Sh LIMITATIONS 2116Word lengths \- 2117Words can be no longer than 1024 characters. 2118The system limits argument lists to 10240 characters. 2119The number of arguments to a command that involves filename expansion 2120is limited to 1/6'th the number of characters allowed in an argument list. 2121Command substitutions may substitute no more characters than are 2122allowed in an argument list. 2123To detect looping, the shell restricts the number of 2124.Ic alias 2125substitutions on a single line to 20. 2126.Sh SEE ALSO 2127.Xr sh 1 , 2128.Xr access 2 , 2129.Xr execve 2 , 2130.Xr fork 2 , 2131.Xr pipe 2 , 2132.Xr setrlimit 2 , 2133.Xr sigaction 2 , 2134.Xr umask 2 , 2135.Xr wait 2 , 2136.Xr killpg 3 , 2137.Xr tty 4 , 2138.Xr a.out 5 , 2139.Xr environ 7 , 2140.Xr sysctl 8 , 2141.br 2142.Em "An introduction to the C shell" 2143.Sh HISTORY 2144.Nm 2145appeared in 2146.Bx 3 . 2147It 2148was a first implementation of a command language interpreter 2149incorporating a history mechanism (see 2150.Sx History Substitutions ) , 2151job control facilities (see 2152.Sx Jobs ) , 2153interactive file name 2154and user name completion (see 2155.Sx File Name Completion ) , 2156and a C-like syntax. 2157There are now many shells that also have these mechanisms, plus 2158a few more (and maybe some bugs too), which are available through the 2159usenet. 2160.Sh BUGS 2161When a command is restarted from a stop, 2162the shell prints the directory it started in if this is different 2163from the current directory; this can be misleading (i.e., wrong) 2164as the job may have changed directories internally. 2165.Pp 2166Shell builtin functions are not stoppable/restartable. 2167Command sequences of the form `a ; b ; c' are also not handled gracefully 2168when stopping is attempted. If you suspend `b', the shell will 2169immediately execute `c'. This is especially noticeable if this 2170expansion results from an 2171.Ar alias . 2172It suffices to place the sequence of commands in ()'s to force it to 2173a subshell, i.e., `( a ; b ; c )'. 2174.Pp 2175Control over tty output after processes are started is primitive; 2176perhaps this will inspire someone to work on a good virtual 2177terminal interface. In a virtual terminal interface much more 2178interesting things could be done with output control. 2179.Pp 2180Alias substitution is most often used to clumsily simulate shell procedures; 2181shell procedures should be provided instead of aliases. 2182.Pp 2183Commands within loops, prompted for by `?', are not placed on the 2184.Ic history 2185list. 2186Control structure should be parsed instead of being recognized as built-in 2187commands. This would allow control commands to be placed anywhere, 2188to be combined with `\&|', and to be used with `&' and `;' metasyntax. 2189.Pp 2190It should be possible to use the `:' modifiers on the output of command 2191substitutions. 2192.Pp 2193The way the 2194.Ic filec 2195facility is implemented is ugly and expensive. 2196