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1.1 ! root 1: .ds OK [\| ! 2: .ds CK \|] ! 3: .TH SH 1 ! 4: .CT 1 shell proc_man dirs files ! 5: .SH NAME ! 6: sh, cd, wait, whatis \- shell, the standard command programming language ! 7: .SH SYNOPSIS ! 8: .B sh ! 9: [ ! 10: .B -acefiknpstuvx ! 11: ] ! 12: [ ! 13: .I args ! 14: ] ! 15: .SH DESCRIPTION ! 16: .I Sh ! 17: is a command programming language ! 18: that executes commands read from a terminal ! 19: or a file. ! 20: See `Invocation' below ! 21: for the meaning of arguments to the shell. ! 22: .SS Definitions ! 23: A ! 24: .I blank ! 25: is a tab or a space. ! 26: A ! 27: .I name ! 28: is a sequence of letters, digits, or underscores beginning with a letter ! 29: or underscore. ! 30: A ! 31: .I parameter ! 32: is a name, a digit, or any of the characters ! 33: .BR \(** , ! 34: .BR @ , ! 35: .BR # , ! 36: .BR ? , ! 37: .BR - , ! 38: .BR $ , ! 39: and ! 40: .BR !\\^ . ! 41: A ! 42: .I word ! 43: is a sequence of characters and quoted strings set off by operators, ! 44: blanks, or newlines; see `Quoting'. ! 45: .SS Commands ! 46: A ! 47: .I simple-command ! 48: is a sequence of ! 49: .I words ! 50: separated by ! 51: .IR blanks . ! 52: The first word specifies the name of the command to ! 53: be executed. ! 54: Except as specified below, ! 55: the remaining words are passed as arguments ! 56: to the invoked command. ! 57: The command name is passed as argument 0; see ! 58: .IR exec (2). ! 59: The ! 60: .I value ! 61: of a simple-command is its exit status ! 62: if it terminates normally, or ! 63: .BR 0200+ status ! 64: if it terminates abnormally; see ! 65: .IR signal (2) ! 66: for a list of ! 67: status values. ! 68: .PP ! 69: A ! 70: .I pipeline ! 71: is a sequence of one or more ! 72: .I commands ! 73: separated by ! 74: .BR | . ! 75: If there is more than one command, each is run ! 76: in a subshell; ! 77: .B | ! 78: denotes a ! 79: .IR pipe (2) ! 80: connecting the standard output of one command to the standard input ! 81: of the next. ! 82: Each command is run as a separate process; ! 83: the shell waits for the last command to terminate. ! 84: The exit status of a pipeline is the exit status of the last command. ! 85: .PP ! 86: A ! 87: .I list ! 88: is a sequence of one or more ! 89: pipelines ! 90: separated by ! 91: .BR ; , ! 92: .BR & , ! 93: .BR && , ! 94: or ! 95: .BR || , ! 96: and terminated by ! 97: .B ; ! 98: or ! 99: .BR & . ! 100: Of these four symbols, ! 101: .B ; ! 102: and ! 103: .B & ! 104: have equal precedence, ! 105: which is lower than that of ! 106: .B && ! 107: and ! 108: .BR || . ! 109: The symbols ! 110: .B && ! 111: and ! 112: .B || ! 113: also have equal precedence. ! 114: A semicolon ! 115: .RB ( ; ) ! 116: causes sequential execution of the preceding pipeline; an ampersand ! 117: .RB ( & ) ! 118: causes asynchronous execution of the pipeline; the shell does not ! 119: wait and proceeds as if the pipeline ! 120: had returned zero exit status. ! 121: The symbol ! 122: .B && ! 123: .RB ( || ) ! 124: causes the ! 125: .I list ! 126: following it to be executed only if the preceding ! 127: pipeline ! 128: returns a zero (non-zero) exit status. ! 129: One or more newlines may follow any sequencing operator ! 130: .RB ( "; & && ||" ). ! 131: .PP ! 132: One or more newlines may always be used in place of a single semicolon, ! 133: and newlines may be freely inserted after any of ! 134: .BR "| ; & && || ;; if do then elif else fi done while until" . ! 135: .PP ! 136: A ! 137: .I command ! 138: is either a simple-command ! 139: or one of the following. ! 140: Unless otherwise stated, ! 141: the value returned by a command is that of the ! 142: last simple-command executed in the command. ! 143: .PP ! 144: .PD 0 ! 145: .TP ! 146: \f5for\fP \f2name\fP \*(OK \&\f5in\fP \f2word\fP .\|.\|. \&\f5;\fP \*(CK \ ! 147: \f5do\fP \f2list\fP \f5;\fP \f5done\fP ! 148: A ! 149: .L for ! 150: command executes a ! 151: .I list ! 152: of commands once for each ! 153: .I word, ! 154: with ! 155: .I name ! 156: set to each ! 157: .I word ! 158: in turn. ! 159: If ! 160: .BI in " word" ! 161: .RB .\|.\|. " ;" ! 162: is omitted or replaced by newlines, then ! 163: the ! 164: .I list ! 165: is executed once for each positional parameter ! 166: that is set; see `Parameter Substitution'. ! 167: .TP ! 168: \f5case\fP \f2word\fP \&\f5in\fP \*(OK \f2pattern\fP \*(OK | \ ! 169: \f2pattern\fP \*(CK .\|.\|. \&\f5)\fP \f2list\fP \&\f5;;\fP \*(CK .\|.\|. \f5esac\fP ! 170: A ! 171: .L case ! 172: command executes the ! 173: .I list ! 174: associated with the first ! 175: .I pattern ! 176: that matches ! 177: .IR word . ! 178: The form of the patterns is ! 179: the same as that used for ! 180: file-name generation (see `File Name Generation') ! 181: except that a slash, a leading dot, or a dot immediately ! 182: following a slash need not be matched explicitly. ! 183: Newlines may precede each ! 184: .IR pattern ! 185: and replace the last ! 186: .B ;; ! 187: before ! 188: .BR esac . ! 189: .TP ! 190: \f5if\fP \f2list\fP \&\f5then\fP \f2list\fP \*(OK \ ! 191: \&\f5elif\fP \f2list\fP \&\f5then\fP \f2list\fP \*(CK .\|.\|. \ ! 192: \*(OK \&\f5else\fP \f2list\fP \*(CK \&\f5f\&i\fP ! 193: The ! 194: .I list ! 195: following ! 196: .L if ! 197: is executed and, if it ! 198: returns a zero exit status, the ! 199: .I list ! 200: following ! 201: the first ! 202: .L then ! 203: is executed. ! 204: Otherwise, the ! 205: .I lists ! 206: in ! 207: .L elif ! 208: clauses are executed in turn until one returns zero status; ! 209: then the ! 210: .I list ! 211: following ! 212: the next ! 213: .L then ! 214: is executed. ! 215: Otherwise, the ! 216: .L else ! 217: .I list ! 218: is executed. ! 219: If no ! 220: .L else ! 221: .I list ! 222: or ! 223: .L then ! 224: .I list ! 225: is executed, then the ! 226: .B if ! 227: command returns a zero exit status. ! 228: .TP ! 229: \f5while\fP \f2list\fP \&\f5do\fP \f2list\fP \&\f5done\fP ! 230: A ! 231: .L while ! 232: command repeatedly executes the ! 233: .L while ! 234: .I list ! 235: and, if the exit status of the last command in the list is zero, executes ! 236: the ! 237: .L do ! 238: .IR list ; ! 239: otherwise the loop terminates. ! 240: If no commands in the ! 241: .L do ! 242: .I list ! 243: are executed, then the ! 244: .L while ! 245: command returns a zero exit status; ! 246: .L until ! 247: may be used in place of ! 248: .L while ! 249: to negate ! 250: the loop termination test. ! 251: .TP ! 252: \f5(\fP\f2list\^\f5)\fP ! 253: .br ! 254: Execute ! 255: .I list ! 256: in a sub-shell. ! 257: .TP ! 258: \f5{\fP\f2list\^\fP\f5}\fR ! 259: .br ! 260: .I list ! 261: is simply executed. ! 262: .TP ! 263: \f2name\fP \f5() \f2command\fP ! 264: Define a function ! 265: which is referenced by ! 266: .I name. ! 267: The body of the function ! 268: is the ! 269: .IR command . ! 270: The most useful form of ! 271: .I command ! 272: is a sequence of commands enclosed in braces ! 273: .BR "{ }" . ! 274: Execution of functions is described under ! 275: .IR Execution ! 276: below. ! 277: .PD ! 278: .PP ! 279: These words ! 280: are only recognized as the first word of a command and when not quoted: ! 281: .B ! 282: if then else elif fi case esac for while until do done\fR. ! 283: .SS Comments ! 284: A word beginning with ! 285: .B # ! 286: causes that word and all the following characters up to a newline ! 287: to be ignored. ! 288: .SS Command Substitution ! 289: The standard output from a command enclosed in ! 290: a pair of grave accents ! 291: .B ` ` ! 292: may be used as part or all ! 293: of a word; ! 294: trailing newlines are removed. ! 295: .SS Parameter Substitution ! 296: The character ! 297: .B $ ! 298: is used to introduce substitutable ! 299: .IR parameters . ! 300: There are two types of parameters, ! 301: positional and keyword. ! 302: If ! 303: .I parameter ! 304: is a digit, it is a positional parameter. ! 305: Positional parameters may be assigned values by ! 306: .BR set . ! 307: Keyword parameters (also known as variables) ! 308: may be assigned values by writing: ! 309: .RS ! 310: .PP ! 311: .IB name = value ! 312: \*(OK ! 313: .IB name = value ! 314: \*(CK .\|.\|. ! 315: .RE ! 316: .PP ! 317: Pattern-matching is not performed on ! 318: .IR value . ! 319: There cannot be a function and a variable with the same ! 320: .IR name . ! 321: .PP ! 322: .PD 0 ! 323: .TP ! 324: \f5${\fP\f2parameter\^\fP\f5}\fP ! 325: The value, if any, of the parameter is substituted. ! 326: The braces are required only when ! 327: .I parameter ! 328: is followed by a letter, digit, or underscore ! 329: that is not to be interpreted as part of its name. ! 330: If ! 331: .I parameter ! 332: is ! 333: .B \(** ! 334: or ! 335: .BR @ , ! 336: all the positional ! 337: parameters, starting with ! 338: .BR $1 , ! 339: are substituted ! 340: (separated by spaces). ! 341: Parameter ! 342: .B $0 ! 343: is set from argument zero when the shell ! 344: is invoked. ! 345: .TP ! 346: \f5${\fP\f2parameter\^\fP\f5:-\fP\f2word\^\fP\f5}\fP ! 347: If ! 348: .I parameter ! 349: is set and is non-null, substitute its value; ! 350: otherwise substitute ! 351: .IR word . ! 352: .TP ! 353: \f5${\fP\f2parameter\^\fP\f5:=\fP\f2word\^\fP\f5}\fP ! 354: If ! 355: .I parameter ! 356: is not set or is null ! 357: set it to ! 358: .IR word ; ! 359: the value of the parameter is substituted. ! 360: Positional parameters may not be assigned to ! 361: in this way. ! 362: .TP ! 363: \f5${\fP\f2parameter\^\fP\f5:?\fP\f2word\^\fP\f5}\fP ! 364: If ! 365: .I parameter ! 366: is set and is non-null, substitute its value; ! 367: otherwise, print ! 368: .I word ! 369: and exit from the shell. ! 370: If ! 371: .I word ! 372: is omitted, the message ! 373: ``parameter null or not set'' ! 374: is printed. ! 375: .TP ! 376: \f5${\fP\f2parameter\^\fP\f5:+\fP\f2word\^\fP\f5}\fP ! 377: If ! 378: .I parameter ! 379: is set and is non-null, substitute ! 380: .IR word ; ! 381: otherwise substitute nothing. ! 382: .PD ! 383: .PP ! 384: In the above, ! 385: .I word ! 386: is not evaluated unless it is ! 387: to be used as the substituted string, ! 388: so that, in the following example, ! 389: .B pwd ! 390: is executed only if ! 391: .B d ! 392: is not set or is null: ! 393: .IP ! 394: .B echo ${d:-\`pwd\`} ! 395: .PP ! 396: If the colon ! 397: .RB ( : ) ! 398: is omitted from the above expressions, the ! 399: shell only checks whether ! 400: .I parameter ! 401: is set or not. ! 402: .PP ! 403: The following ! 404: parameters ! 405: are automatically set by the shell: ! 406: .RS ! 407: .PD 0 ! 408: .TP ! 409: .B # ! 410: The number of positional parameters in decimal. ! 411: .TP ! 412: .B - ! 413: Flags supplied to the shell on invocation or by ! 414: the ! 415: .B set ! 416: command. ! 417: .TP ! 418: .B ? ! 419: The decimal value returned by the last synchronously executed command; ! 420: see ! 421: .IR exit (2). ! 422: .TP ! 423: .B $ ! 424: The process number of this shell. ! 425: .TP ! 426: .B ! ! 427: The process number of the last background command invoked. ! 428: .PD ! 429: .RE ! 430: .PP ! 431: The following ! 432: parameters ! 433: are used by the shell: ! 434: .RS ! 435: .PD 0 ! 436: .TP ! 437: .B ! 438: .SM HOME ! 439: The default argument (home directory) for the ! 440: .I cd ! 441: command. ! 442: .TP ! 443: .B ! 444: .SM PATH ! 445: The search path for commands; see `Execution'. ! 446: .TP ! 447: .B ! 448: .SM CDPATH ! 449: The search path for the ! 450: .I cd ! 451: command. ! 452: .TP ! 453: .B ! 454: .SM MAIL ! 455: If this parameter is set to the name of a mail file ! 456: the shell informs the user of the arrival of mail ! 457: in the specified file. ! 458: The file is inspected every three minutes. ! 459: .TP ! 460: .B ! 461: .SM HISTORY ! 462: If this parameter is set to the name of a writable file, ! 463: the shell appends interactive input to the file, for use by the command ! 464: .IR = (1). ! 465: .TP ! 466: .SM ! 467: .B PS1 ! 468: Primary prompt string, by default ! 469: .LR $ . ! 470: .TP ! 471: .SM ! 472: .B PS2 ! 473: Secondary prompt string, by default ! 474: .LR > . ! 475: .TP ! 476: .SM ! 477: .B IFS ! 478: Internal field separators, ! 479: normally space, tab, and newline. ! 480: .PD ! 481: .RE ! 482: .PP ! 483: The shell gives default values to ! 484: \f5\s-1PATH\s+1\fP, \f5\s-1PS1\s+1\fP, \f5\s-1PS2\s+1\fP and \f5\s-1IFS\s+1\fP. ! 485: .SM ! 486: .B HOME ! 487: is set by ! 488: .IR login (8). ! 489: .SS Blank Interpretation ! 490: After parameter and command substitution, ! 491: the results of substitution are scanned for internal field separator ! 492: characters (those found in ! 493: .BR \s-1IFS\s+1 ) ! 494: and split into distinct arguments where such characters are found. ! 495: Explicit null arguments (\^\f5"\^"\fP or \f5\'\^\'\fP\^) are retained. ! 496: Implicit null arguments ! 497: (those resulting from ! 498: .I parameters ! 499: that have no values) are removed. ! 500: .SS File Name Generation ! 501: Following substitution, each command ! 502: .I word ! 503: is scanned for ! 504: the characters ! 505: .BR \(** , ! 506: .BR ? , ! 507: and ! 508: .BR \*(OK . ! 509: If one of these characters appears ! 510: the word is regarded as a ! 511: .IR pattern . ! 512: The word is replaced with alphabetically sorted file names that match the pattern. ! 513: If no file name is found that matches the pattern, ! 514: the word is left unchanged. ! 515: The directories ! 516: .B . ! 517: and ! 518: .B .. ! 519: (initially or after a ! 520: .BR / ) ! 521: are only matched by patterns beginning ! 522: with an explicit period. ! 523: The character ! 524: .B / ! 525: itself must be matched explicitly. ! 526: .PP ! 527: .PD 0 ! 528: .RS ! 529: .TP ! 530: .B \(** ! 531: Matches any string, including the null string. ! 532: .TP ! 533: .B ? ! 534: Matches any single character. ! 535: .TP ! 536: .BR \*(OK .\|.\|. \*(CK ! 537: Matches any one of the enclosed characters. ! 538: A pair of characters separated by ! 539: .B - ! 540: matches any ! 541: character lexically between the pair, inclusive. ! 542: If the first character following the opening ! 543: .L \*(OK ! 544: is a ! 545: .L ^ ! 546: any character not enclosed is matched. ! 547: .PD ! 548: .RE ! 549: .SS Quoting ! 550: These characters have a special meaning to the shell ! 551: and terminate a word unless quoted: ! 552: .IP ! 553: .L ! 554: ; & ( ) | < > { } ! 555: newline space tab ! 556: .PP ! 557: (The characters \f5{\fP and \f5}\fP need not be quoted inside a \f5${\^}\fP construction.) ! 558: A character may be ! 559: .I quoted ! 560: (i.e., made to stand for itself) ! 561: by preceding ! 562: it with a ! 563: .BR \e . ! 564: The pair ! 565: .BR \e newline ! 566: is ignored. ! 567: All characters enclosed between a pair of single quote marks \f5\'\^\'\fP\^ ! 568: (except a single quote) ! 569: are quoted. ! 570: Inside double quote marks ! 571: \f5"\^"\fP ! 572: parameter and command substitution occurs and ! 573: .B \e ! 574: quotes the characters ! 575: .BR \e , ! 576: .BR \` , ! 577: \f5"\fP, ! 578: and ! 579: .BR $ . ! 580: .B ! 581: "$\(**" ! 582: is equivalent to ! 583: \f5"$1 \|$2\fP \|.\|.\|.\f5"\fP, ! 584: whereas ! 585: .B ! 586: "$@" ! 587: is equivalent to ! 588: .B ! 589: "$1"\| ! 590: .B ! 591: "$2"\| ! 592: \&.\|.\|.\|. ! 593: .SS Prompting ! 594: When used interactively, ! 595: the shell prompts with the value of ! 596: .SM ! 597: .B PS1 ! 598: before reading a command. ! 599: If at any time a newline is typed and further input is needed ! 600: to complete a command, the secondary prompt ! 601: (i.e., the value of ! 602: .BR \s-1PS2\s+1 ) ! 603: is issued. ! 604: .SS Input/Output ! 605: Before a command is executed, its input and output ! 606: may be redirected using a special notation interpreted by the shell. ! 607: The following may appear anywhere in a simple-command ! 608: or may precede or follow a ! 609: .I command ! 610: and are not ! 611: passed on to the invoked command; ! 612: substitution occurs before ! 613: .I word ! 614: or ! 615: .I digit ! 616: is used: ! 617: .PP ! 618: .PD 0 ! 619: .TP 14 ! 620: .BI < word ! 621: Use file ! 622: .I word ! 623: as standard input (file descriptor 0). ! 624: .TP ! 625: .BI > word ! 626: Use file ! 627: .I word ! 628: as standard output (file descriptor 1). ! 629: If the file does not exist it is created; ! 630: otherwise, it is truncated to zero length. ! 631: .TP ! 632: .BI >> word ! 633: Use file ! 634: .I word ! 635: as standard output. ! 636: If the file exists output is appended to it (by first seeking to the end-of-file); ! 637: otherwise, the file is created. ! 638: .TP ! 639: .BI << word ! 640: The shell input is read up to a line that is the same as ! 641: .IR word , ! 642: or to an end-of-file. ! 643: The resulting document becomes ! 644: the standard input. ! 645: If any character of ! 646: .I word ! 647: is quoted, no interpretation ! 648: is placed upon the characters of the document; ! 649: otherwise, parameter and command substitution occurs, ! 650: (unescaped) ! 651: .BR \e newline ! 652: is ignored, ! 653: and ! 654: .B \e ! 655: must be used to quote the characters ! 656: .BR \e , ! 657: .BR $ , ! 658: .BR \` , ! 659: and the first character of ! 660: .IR word . ! 661: .TP ! 662: .BI <& digit ! 663: Use the file associated with file descriptor ! 664: .I digit ! 665: as standard input. ! 666: Similarly for the standard output using ! 667: .BI >& digit . ! 668: .TP ! 669: .B <&- ! 670: The standard input is closed. ! 671: Similarly for the standard output using ! 672: .BR >&- . ! 673: .PD ! 674: .PP ! 675: If any of the above is preceded by a digit, ! 676: the ! 677: file descriptor which will be associated with the file ! 678: is that specified ! 679: by the digit ! 680: (instead of the default 0 or 1). ! 681: For example: ! 682: .IP ! 683: .RB .\|.\|. " 2>&1" ! 684: .PP ! 685: associates file descriptor 2 with the file currently associated with ! 686: file descriptor 1. ! 687: .PP ! 688: The order in which redirections are specified is significant. ! 689: The shell evaluates redirections left-to-right. ! 690: For example: ! 691: .IP ! 692: .RB .\|.\|. " 1>xxx 2>&1" ! 693: .PP ! 694: first associates file descriptor 1 with file ! 695: .LR xxx , ! 696: then associates file descriptor 2 with the same file as ! 697: descriptor 1, namely ! 698: .LR xxx , ! 699: while ! 700: .IP ! 701: .RB .\|.\|. " 2>&1 1>xxx" ! 702: .PP ! 703: associates file descriptor 2 ! 704: with the current value of file descriptor 1 (typically the terminal) ! 705: and file descriptor 1 with ! 706: .LR xxx . ! 707: .PP ! 708: If a command is followed by ! 709: .BR & , ! 710: the default standard input ! 711: for the command ! 712: is the empty file ! 713: .BR /dev/null . ! 714: Otherwise, the environment for the execution of a command contains the ! 715: file descriptors of the invoking shell as modified by ! 716: input/output specifications. ! 717: .SS Environment ! 718: The ! 719: .I environment ! 720: is a list of strings, conventionally function definitions ! 721: and name-value pairs, that is passed to ! 722: an executed program in the same way as a normal argument list; see ! 723: .IR environ (5). ! 724: The shell interacts with the environment in several ways. ! 725: On invocation, the shell scans the environment ! 726: and creates a ! 727: parameter or function ! 728: for each name found, ! 729: giving it the corresponding value. ! 730: If the user modifies the value of any of these ! 731: parameters ! 732: or creates new parameters, ! 733: none of these affects the environment ! 734: unless the ! 735: .B export ! 736: command is used to bind the shell's ! 737: parameter ! 738: to the environment; see also ! 739: .BR "set -a" . ! 740: A parameter may be removed from the environment ! 741: with the ! 742: .B unset ! 743: command. ! 744: The environment seen by any executed command is thus composed ! 745: of any unmodified name-value pairs originally inherited by the shell, ! 746: minus any pairs removed by ! 747: .BR unset , ! 748: plus any modifications or additions, ! 749: all of which must be noted in ! 750: .B export ! 751: commands. ! 752: .PP ! 753: The environment for any ! 754: .I simple-command ! 755: may be augmented by prefixing it with one or more assignments to ! 756: parameters (but not functions). ! 757: Thus ! 758: .L tabs ! 759: gets the same environment in both lines below, ! 760: but the shell has one less variable in the second. ! 761: .IP ! 762: .B (export TERM; TERM=450; cmd) ! 763: .br ! 764: .B TERM=450 cmd ! 765: .PP ! 766: If the ! 767: .B -k ! 768: flag is set, ! 769: .I all ! 770: keyword arguments are placed in the environment, ! 771: even if they occur after the command name. ! 772: .SS Signals ! 773: .B SIGINT ! 774: and ! 775: .B SIGQUIT ! 776: (see ! 777: .IR signal (2)) ! 778: for an invoked ! 779: command are ignored if the command is followed by ! 780: .BR & ; ! 781: otherwise signals have the values ! 782: inherited by the shell from its parent ! 783: (but see also ! 784: the ! 785: .B trap ! 786: command below). ! 787: .SS Execution ! 788: Each time a command is executed, the above substitutions are ! 789: carried out. ! 790: If the command name matches the name of a defined function, the function is executed ! 791: in the shell process. ! 792: (Note how this differs from calling a shell script.) ! 793: The positional parameters ! 794: .BR $1 , ! 795: .BR $2 , ! 796: \&.\|.\|.\|. ! 797: are set to the arguments of the function. ! 798: If the command name does not match a function, but matches one of the ! 799: builtin commands ! 800: listed below, it is executed in the shell process. ! 801: If the command name matches neither a ! 802: builtin command ! 803: nor the name of a defined function, ! 804: a new process is created and an attempt is made to ! 805: execute the command via ! 806: .IR exec (2). ! 807: .PP ! 808: The shell parameter ! 809: .B ! 810: .SM PATH ! 811: defines the search path for ! 812: the directory containing the command. ! 813: Alternative directory names are separated by ! 814: a colon ! 815: .RB ( : ). ! 816: The default path is ! 817: .B :/bin:/usr/bin ! 818: (specifying the current directory, ! 819: .BR /bin , ! 820: and ! 821: .BR /usr/bin , ! 822: in that order). ! 823: Note that the current directory is specified by a null path name, ! 824: which can appear immediately after the equal sign ! 825: or between the colon delimiters anywhere else in the path list. ! 826: If the command name contains a \f5/\fP the search path ! 827: is not used. ! 828: Otherwise, each directory in the path is ! 829: searched for an executable file. ! 830: If the file has execute permission but is not executable by ! 831: .IR exec (2), ! 832: it is assumed to be a `shell script', a file of shell commands. ! 833: A sub-shell is spawned to read it. ! 834: A parenthesized command is also executed in ! 835: a sub-shell. ! 836: .SS Builtin Commands ! 837: Input/output redirection is permitted for these commands. ! 838: File descriptor 1 is the default output location. ! 839: .PP ! 840: .PD 0 ! 841: .TP ! 842: .B : ! 843: No effect; the command does nothing. ! 844: A zero exit code is returned. ! 845: .br ! 846: .TP ! 847: .BI ". " file ! 848: Read and execute commands from ! 849: .I file ! 850: and return. ! 851: The search path ! 852: specified by ! 853: .B ! 854: .SM PATH ! 855: is used to find the directory containing ! 856: .IR file . ! 857: .TP ! 858: \f5builtin\fP \*(OK \f2command\fP \*(CK ! 859: Execute the builtin ! 860: .I command ! 861: (such as ! 862: .BR break) ! 863: regardless of functions defined with the same name. ! 864: .TP ! 865: \f5break\fP \*(OK \f2n\fP \*(CK ! 866: Exit from the enclosing \f5for\fP or ! 867: .B while ! 868: loop, if any. ! 869: If ! 870: .I n ! 871: is specified break ! 872: .I n ! 873: levels. ! 874: .TP ! 875: \f5continue\fP \*(OK \f2n\fP \*(CK ! 876: Resume the next iteration of the enclosing ! 877: \f5for\fP or ! 878: .B while ! 879: loop. ! 880: If ! 881: .I n ! 882: is specified resume at the ! 883: .IR n -th ! 884: enclosing loop. ! 885: .TP ! 886: \f5cd\fP \*(OK \f2arg\fP \*(CK ! 887: Change the current directory to ! 888: .I arg. ! 889: The shell ! 890: parameter ! 891: .B ! 892: .SM HOME ! 893: is the default ! 894: .I arg. ! 895: The shell parameter ! 896: .B ! 897: .SM CDPATH ! 898: defines the search path for ! 899: the directory containing ! 900: .IR arg . ! 901: Alternative directory names are separated by ! 902: a colon ! 903: .RB ( : ). ! 904: The current directory (default) is specified by a null path name, ! 905: which can appear immediately after the equal sign ! 906: or between the colon delimiters anywhere else in the path list. ! 907: If ! 908: .I arg ! 909: begins with a ! 910: .L / ! 911: the search path ! 912: is not used. ! 913: Otherwise, each directory in the path is ! 914: searched for ! 915: .I arg. ! 916: .TP ! 917: \f5eval\fP \*(OK \f2arg\fP .\|.\|. \*(CK ! 918: The arguments are read as input ! 919: to the shell ! 920: and the resulting command(s) executed. ! 921: .TP ! 922: \f5exec\fP \*(OK \f2arg\fP .\|.\|. \*(CK ! 923: The non-builtin command specified by ! 924: the arguments is executed in place of this shell ! 925: without creating a new process. ! 926: Input/output arguments may appear and, if no other ! 927: arguments are given, cause the shell ! 928: input/output to be modified. ! 929: .TP ! 930: \f5exit\fP \*(OK \f2n\fP \*(CK ! 931: Causes a shell to exit ! 932: with the exit status specified by ! 933: .IR n . ! 934: If ! 935: .I n ! 936: is omitted the exit status is that of the last command executed ! 937: (an end-of-file will also cause the shell to exit.) ! 938: .TP ! 939: \f5export\fP \*(OK \f2name\fP .\|.\|. \*(CK ! 940: The given ! 941: .I names ! 942: are marked ! 943: for automatic export to the ! 944: .I environment ! 945: of subsequently-executed commands. ! 946: If no arguments are given, a list of all ! 947: names that are exported in this shell is printed. ! 948: .TP ! 949: \f5read\fP \*(OK \f2name\fP .\|.\|. \*(CK ! 950: One line is read from the standard input and ! 951: the first ! 952: word is assigned to the first ! 953: .I name, ! 954: the second word ! 955: to the second ! 956: .I name, ! 957: etc., with leftover words assigned to the last ! 958: .I name. ! 959: The return code is 0 unless an end-of-file is encountered. ! 960: .TP ! 961: \f5return\fP \*(OK \f2n\fP \*(CK ! 962: Causes a function to exit with the return value specified by ! 963: .I n. ! 964: If ! 965: .I n ! 966: is omitted, the return status is that of the last command executed. ! 967: .TP ! 968: \f5set\fP \*(OK \f5--aehknptuvx\fP \*(OK \f2arg\fP .\|.\|. \*(CK \*(CK ! 969: .RS ! 970: .TP ! 971: .B -a ! 972: Mark variables which are modified or created for export. ! 973: .TP ! 974: .B -e ! 975: Exit immediately if a command ! 976: exits with a non-zero exit status. ! 977: .TP ! 978: .B -f ! 979: Disable file name generation ! 980: .TP ! 981: .B -k ! 982: All keyword arguments are placed in the environment for a command, ! 983: not just those that precede the command name. ! 984: .TP ! 985: .B -n ! 986: Read commands but do not execute them. ! 987: .TP ! 988: .B -p ! 989: Remove the definitions for all functions imported from the environment, ! 990: and set ! 991: .B IFS ! 992: to blank, tab and newline. ! 993: .TP ! 994: .B -t ! 995: Exit after reading and executing one command. ! 996: .TP ! 997: .B -u ! 998: Treat unset variables as an error when substituting. ! 999: .TP ! 1000: .B -v ! 1001: Print shell input lines as they are read. ! 1002: .TP ! 1003: .B -x ! 1004: Print commands and their arguments as they are executed. ! 1005: .TP ! 1006: .B -- ! 1007: Do not change any of the flags; useful in setting ! 1008: .B $1 ! 1009: to ! 1010: .BR - . ! 1011: .PP ! 1012: Using ! 1013: .B \+ ! 1014: rather than ! 1015: .B - ! 1016: causes these flags to be turned off. ! 1017: These flags can also be used upon invocation of the shell. ! 1018: The current set of flags may be found in ! 1019: .BR $- . ! 1020: The remaining arguments are positional ! 1021: parameters and are assigned, in order, to ! 1022: .BR $1 , ! 1023: .BR $2 , ! 1024: \&.\|.\|.\|. ! 1025: If no arguments are given the values ! 1026: of all names are printed. ! 1027: .RE ! 1028: .TP ! 1029: \f5shift\fP \*(OK \f2n\fP \*(CK ! 1030: .br ! 1031: The positional parameters from ! 1032: .BI $ n\fR+1 ! 1033: \&.\|.\|. ! 1034: are renamed ! 1035: .B $1 ! 1036: \&.\|.\|. ! 1037: If ! 1038: .I n ! 1039: is not given, it is assumed to be 1. ! 1040: .TP ! 1041: \f5times\fP ! 1042: .br ! 1043: Print the accumulated user and system times for processes ! 1044: run from the shell. ! 1045: .TP ! 1046: \f5trap\fP \*(OK \f2arg\fP \*(CK \*(OK \f2n\fP \*(CK .\|.\|. ! 1047: The command ! 1048: .I arg ! 1049: is to be read and executed when the shell ! 1050: receives signal(s) ! 1051: .IR n . ! 1052: (Note that ! 1053: .I arg ! 1054: is scanned once when ! 1055: the trap is set and once when the trap ! 1056: is taken.) ! 1057: Trap commands are executed in order of signal number. ! 1058: Any attempt to set a trap on a signal that ! 1059: was ignored on entry to the current shell ! 1060: is ineffective. ! 1061: If ! 1062: .I arg ! 1063: is absent all traps ! 1064: .I n ! 1065: are reset ! 1066: to their original values. ! 1067: If ! 1068: .I arg ! 1069: is the null ! 1070: string this signal is ignored by the shell and by the commands ! 1071: it invokes. ! 1072: If ! 1073: .I n ! 1074: is 0 the command ! 1075: .I arg ! 1076: is executed ! 1077: on exit from the shell. ! 1078: The ! 1079: .B trap ! 1080: command ! 1081: with no arguments prints a list ! 1082: of commands associated with each signal number. ! 1083: .TP ! 1084: \f5umask\fP \*(OK \f2nnn\fP \*(CK ! 1085: The user file-creation mask is set to ! 1086: .IR nnn ; ! 1087: see ! 1088: .IR umask (2). ! 1089: If ! 1090: .I nnn ! 1091: is omitted, the current value of the mask is printed. ! 1092: .TP ! 1093: \f5unset\fP \*(OK \f2name\fP .\|.\|. \*(CK ! 1094: For each ! 1095: .IR name , ! 1096: remove the corresponding variable or function. ! 1097: The variables ! 1098: \f5\s-1PATH\s+1\fP, \f5\s-1PS1\s+1\fP, \f5\s-1PS2\s+1\fP and \f5\s-1IFS\s+1\fP ! 1099: cannot be unset. ! 1100: .TP ! 1101: \f5wait\fP \*(OK \f2n\fP \*(CK ! 1102: Wait for the specified process and report its termination status. ! 1103: If ! 1104: .I n ! 1105: is not given all currently active child processes are waited for ! 1106: and the return code is zero. ! 1107: .TP ! 1108: \f5whatis\fP \*(OK \fIname\fP .\|.\|. \*(CK ! 1109: For each ! 1110: .IR name , ! 1111: print the associated value as a parameter, function, builtin or executable ! 1112: binary as appropriate. ! 1113: In each case, the value is printed in a form that would yield the same ! 1114: value if typed as input to the shell itself: ! 1115: parameters are printed as assignments, functions as their definitions, ! 1116: builtins as calls to ! 1117: .BR builtin , ! 1118: and binaries as their full pathnames. ! 1119: .PD ! 1120: .PP ! 1121: .SS Invocation ! 1122: Normally the shell reads commands from the file named in its ! 1123: first argument (standard input default). ! 1124: The remaining arguments are interpreted as position parameters; see ! 1125: `Parameter substitution' above. ! 1126: If the shell is invoked through ! 1127: .IR exec (2) ! 1128: and the first character of argument zero ! 1129: is ! 1130: .BR - , ! 1131: commands are read first from ! 1132: .BR $HOME/.profile , ! 1133: if it exists. ! 1134: Certain options modify this behavior: ! 1135: .PP ! 1136: .PD 0 ! 1137: .TP 10 ! 1138: .BI -c "\| string" ! 1139: Read commands from ! 1140: .IR string ; ! 1141: ignore remaining arguments. ! 1142: .TP ! 1143: .B -s ! 1144: Write shell output (except for builtin commands) ! 1145: on file descriptor 2. ! 1146: .TP ! 1147: .B -i ! 1148: Interactive. ! 1149: Ignore signal ! 1150: .B SIGTERM ! 1151: (interactive shell is immune to ! 1152: .BR "kill 0" ). ! 1153: Catch and ignore ! 1154: .B SIGINT ! 1155: .RB ( wait ! 1156: is interruptible). ! 1157: The shell always ignores ! 1158: .BR SIGQUIT . ! 1159: .PD ! 1160: .PP ! 1161: Other options are described under the ! 1162: .B set ! 1163: command above. ! 1164: .SH FILES ! 1165: .F $HOME/.profile ! 1166: .br ! 1167: .F /tmp/sh* ! 1168: .br ! 1169: .F /dev/null ! 1170: .SH SEE ALSO ! 1171: .IR = (1), ! 1172: .IR echo (1), ! 1173: .IR newgrp (1), ! 1174: .IR test (1), ! 1175: .IR dup (2), ! 1176: .IR exec (2), ! 1177: .IR fork (2), ! 1178: .IR pipe (2), ! 1179: .IR signal (2), ! 1180: .IR umask (2), ! 1181: .IR exit (2), ! 1182: .IR environ (5) ! 1183: .br ! 1184: B. W. Kernighan and R. Pike, ! 1185: .I The Unix Programming Environment, ! 1186: Prentice-Hall, 1984 ! 1187: .SH DIAGNOSTICS ! 1188: Errors detected by the shell, such as syntax errors, ! 1189: cause the shell ! 1190: to return a non-zero exit status. ! 1191: If the shell is being used non-interactively ! 1192: execution of the shell file is abandoned. ! 1193: Otherwise, the shell returns the exit status of ! 1194: the last command executed; see also the ! 1195: .B exit ! 1196: command. ! 1197: .SH BUGS ! 1198: Errors arising from builtins terminate shell scripts.
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