rc.1 (20154B)
1 .TH RC 1 2 .SH NAME 3 rc, cd, eval, exec, exit, flag, rfork, shift, wait, whatis, ., ~ \- command language 4 .SH SYNOPSIS 5 .B rc 6 [ 7 .B -srdiIlxepvV 8 ] 9 [ 10 .B -c command 11 ] 12 [ 13 .I file 14 [ 15 .I arg ... 16 ]] 17 .SH DESCRIPTION 18 .I Rc 19 is the Plan 9 shell. 20 It executes command lines read from a terminal or a file or, with the 21 .B -c 22 flag, from 23 .I rc's 24 argument list. 25 .SS Command Lines 26 A command line is a sequence of commands, separated by ampersands or semicolons 27 .RB ( & 28 or 29 .BR ; ), 30 terminated by a newline. 31 The commands are executed in sequence 32 from left to right. 33 .I Rc 34 does not wait for a command followed by 35 .B & 36 to finish executing before starting 37 the following command. 38 Whenever a command followed by 39 .B & 40 is executed, its process id is assigned to the 41 .I rc 42 variable 43 .BR $apid . 44 Whenever a command 45 .I not 46 followed by 47 .B & 48 exits or is terminated, the 49 .I rc 50 variable 51 .B $status 52 gets the process's wait message (see 53 .IR wait (3)); 54 it will be the null string if the command was successful. 55 .PP 56 A long command line may be continued on subsequent lines by typing 57 a backslash 58 .RB ( \e ) 59 followed by a newline. 60 This sequence is treated as though it were a blank. 61 Backslash is not otherwise a special character. 62 .PP 63 A number-sign 64 .RB ( # ) 65 and any following characters up to (but not including) the next newline 66 are ignored, except in quotation marks. 67 .SS Simple Commands 68 A simple command is a sequence of arguments interspersed with I/O redirections. 69 If the first argument is the name of an 70 .I rc 71 function or of one of 72 .I rc's 73 built-in commands, it is executed by 74 .IR rc . 75 Otherwise if the name starts with a slash 76 .RB ( / ), 77 it must be the path name of the program to be executed. 78 Names containing no initial slash are searched for in 79 a list of directory names stored in 80 .BR $path . 81 The first executable file of the given name found 82 in a directory in 83 .B $path 84 is the program to be executed. 85 To be executable, the user must have execute permission (see 86 .IR stat (3)) 87 and the file must be either an executable binary 88 for the current machine's CPU type, or a shell script. 89 Shell scripts begin with a line containing the full path name of a shell 90 (usually 91 .BR /bin/rc ), 92 prefixed by 93 .LR #! . 94 .PP 95 The first word of a simple command cannot be a keyword unless it is 96 quoted or otherwise disguised. 97 The keywords are 98 .EX 99 for in while if not switch fn ~ ! @ 100 .EE 101 .SS Arguments and Variables 102 A number of constructions may be used where 103 .I rc's 104 syntax requires an argument to appear. 105 In many cases a construction's 106 value will be a list of arguments rather than a single string. 107 .PP 108 The simplest kind of argument is the unquoted word: 109 a sequence of one or more characters none of which is a blank, tab, 110 newline, or any of the following: 111 .EX 112 # ; & | ^ $ = ` ' { } ( ) < > 113 .EE 114 An unquoted word that contains any of the characters 115 .B * 116 .B ? 117 .B [ 118 is a pattern for matching against file names. 119 The character 120 .B * 121 matches any sequence of characters, 122 .B ? 123 matches any single character, and 124 .BI [ class ] 125 matches any character in the 126 .IR class . 127 If the first character of 128 .I class 129 is 130 .BR ~ , 131 the class is complemented. 132 The 133 .I class 134 may also contain pairs of characters separated by 135 .BR - , 136 standing for all characters lexically between the two. 137 The character 138 .B / 139 must appear explicitly in a pattern, as must the 140 first character of the path name components 141 .B . 142 and 143 .BR .. . 144 A pattern is replaced by a list of arguments, one for each path name matched, 145 except that a pattern matching no names is not replaced by the empty list, 146 but rather stands for itself. 147 Pattern matching is done after all other 148 operations. 149 Thus, 150 .EX 151 x=/tmp echo $x^/*.c 152 .EE 153 matches 154 .BR /tmp/*.c , 155 rather than matching 156 .B "/*.c 157 and then prefixing 158 .BR /tmp . 159 .PP 160 A quoted word is a sequence of characters surrounded by single quotes 161 .RB ( ' ). 162 A single quote is represented in a quoted word by a pair of quotes 163 .RB ( '' ). 164 .PP 165 Each of the following is an argument. 166 .PD 0 167 .HP 168 .BI ( arguments ) 169 .br 170 The value of a sequence of arguments enclosed in parentheses is 171 a list comprising the members of each element of the sequence. 172 Argument lists have no recursive structure, although their syntax may 173 suggest it. 174 The following are entirely equivalent: 175 .EX 176 echo hi there everybody 177 ((echo) (hi there) everybody) 178 .EE 179 .HP 180 .BI $ argument 181 .HP 182 .BI $ argument ( subscript ) 183 .br 184 The 185 .I argument 186 after the 187 .B $ 188 is the name of a variable whose value is substituted. 189 Multiple levels 190 of indirection are possible, but of questionable utility. 191 Variable values 192 are lists of strings. 193 If 194 .I argument 195 is a number 196 .IR n , 197 the value is the 198 .IR n th 199 element of 200 .BR $* , 201 unless 202 .B $* 203 doesn't have 204 .I n 205 elements, in which case the value is empty. 206 If 207 .I argument 208 is followed by a parenthesized list of subscripts, the 209 value substituted is a list composed of the requested elements (origin 1). 210 The parenthesis must follow the variable name with no spaces. 211 Subscripts can also take the form 212 .IB m - n 213 or 214 .IB m - 215 to indicate a sequence of elements. 216 Assignments to variables are described below. 217 .HP 218 .BI $# argument 219 .br 220 The value is the number of elements in the named variable. 221 A variable 222 never assigned a value has zero elements. 223 .HP 224 $"\c 225 .I argument 226 .br 227 The value is a single string containing the components of the named variable 228 separated by spaces. A variable with zero elements yields the empty string. 229 .HP 230 .BI `{ command } 231 .br 232 .I rc 233 executes the 234 .I command 235 and reads its standard output, splitting it into a list of arguments, 236 using characters in 237 .B $ifs 238 as separators. 239 If 240 .B $ifs 241 is not otherwise set, its value is 242 .BR "'\ \et\en'" . 243 .HP 244 .BI <{ command } 245 .HP 246 .BI >{ command } 247 .br 248 The 249 .I command 250 is executed asynchronously with its standard output or standard input 251 connected to a pipe. 252 The value of the argument is the name of a file 253 referring to the other end of the pipe. 254 This allows the construction of 255 non-linear pipelines. 256 For example, the following runs two commands 257 .B old 258 and 259 .B new 260 and uses 261 .B cmp 262 to compare their outputs 263 .EX 264 cmp <{old} <{new} 265 .EE 266 .HP 267 .IB argument ^ argument 268 .br 269 The 270 .B ^ 271 operator concatenates its two operands. 272 If the two operands 273 have the same number of components, they are concatenated pairwise. 274 If not, 275 then one operand must have one component, and the other must be non-empty, 276 and concatenation is distributive. 277 .PD 278 .SS Free Carets 279 In most circumstances, 280 .I rc 281 will insert the 282 .B ^ 283 operator automatically between words that are not separated by white space. 284 Whenever one of 285 .B $ 286 .B ' 287 .B ` 288 follows a quoted or unquoted word or an unquoted word follows a quoted word 289 with no intervening blanks or tabs, 290 a 291 .B ^ 292 is inserted between the two. 293 If an unquoted word immediately follows a 294 .BR $ 295 and contains a character other than an alphanumeric, underscore, 296 or 297 .BR * , 298 a 299 .B ^ 300 is inserted before the first such character. 301 Thus 302 .IP 303 .B cc -$flags $stem.c 304 .LP 305 is equivalent to 306 .IP 307 .B cc -^$flags $stem^.c 308 .SS I/O Redirections 309 The sequence 310 .BI > file 311 redirects the standard output file (file descriptor 1, normally the 312 terminal) to the named 313 .IR file ; 314 .BI >> file 315 appends standard output to the file. 316 The standard input file (file descriptor 0, also normally the terminal) 317 may be redirected from a file by the sequence 318 .BI < file \f1, 319 or from an inline `here document' 320 by the sequence 321 .BI << eof-marker\f1. 322 The contents of a here document are lines of text taken from the command 323 input stream up to a line containing nothing but the 324 .IR eof-marker , 325 which may be either a quoted or unquoted word. 326 If 327 .I eof-marker 328 is unquoted, variable names of the form 329 .BI $ word 330 have their values substituted from 331 .I rc's 332 environment. 333 If 334 .BI $ word 335 is followed by a caret 336 .RB ( ^ ), 337 the caret is deleted. 338 If 339 .I eof-marker 340 is quoted, no substitution occurs. 341 .PP 342 Redirections may be applied to a file-descriptor other than standard input 343 or output by qualifying the redirection operator 344 with a number in square brackets. 345 For example, the diagnostic output (file descriptor 2) 346 may be redirected by writing 347 .BR "cc junk.c >[2]junk" . 348 .PP 349 A file descriptor may be redirected to an already open descriptor by writing 350 .BI >[ fd0 = fd1 ] 351 or 352 .BI <[ fd0 = fd1 ]\f1. 353 .I Fd1 354 is a previously opened file descriptor and 355 .I fd0 356 becomes a new copy (in the sense of 357 .IR dup (3)) 358 of it. 359 A file descriptor may be closed by writing 360 .BI >[ fd0 =] 361 or 362 .BI <[ fd0 =]\f1. 363 .PP 364 Redirections are executed from left to right. 365 Therefore, 366 .B cc junk.c >/dev/null >[2=1] 367 and 368 .B cc junk.c >[2=1] >/dev/null 369 have different effects: the first puts standard output in 370 .BR /dev/null 371 and then puts diagnostic output in the same place, where the second 372 directs diagnostic output to the terminal and sends standard output to 373 .BR /dev/null . 374 .SS Compound Commands 375 A pair of commands separated by a pipe operator 376 .RB ( | ) 377 is a command. 378 The standard output of the left command is sent through a pipe 379 to the standard input of the right command. 380 The pipe operator may be decorated 381 to use different file descriptors. 382 .BI |[ fd ] 383 connects the output end of the pipe to file descriptor 384 .I fd 385 rather than 1. 386 .BI |[ fd0 = fd1 ] 387 connects output to 388 .I fd1 389 of the left command and input to 390 .I fd0 391 of the right command. 392 .PP 393 A pair of commands separated by 394 .B && 395 or 396 .B || 397 is a command. 398 In either case, the left command is executed and its exit status examined. 399 If the operator is 400 .B && 401 the right command is executed if the left command's status is null. 402 .B || 403 causes the right command to be executed if the left command's status is non-null. 404 .PP 405 The exit status of a command may be inverted (non-null is changed to null, null 406 is changed to non-null) by preceding it with a 407 .BR ! . 408 .PP 409 The 410 .B | 411 operator has highest precedence, and is left-associative (i.e. binds tighter 412 to the left than the right). 413 .B ! 414 has intermediate precedence, and 415 .B && 416 and 417 .B || 418 have the lowest precedence. 419 .PP 420 The unary 421 .B @ 422 operator, with precedence equal to 423 .BR ! , 424 causes its operand to be executed in a subshell. 425 .PP 426 Each of the following is a command. 427 .PD 0 428 .HP 429 .B if ( 430 .I list 431 .B ) 432 .I command 433 .br 434 A 435 .I list 436 is a sequence of commands, separated by 437 .BR & , 438 .BR ; , 439 or newline. 440 It is executed and 441 if its exit status is null, the 442 .I command 443 is executed. 444 .HP 445 .B if not 446 .I command 447 .br 448 The immediately preceding command must have been 449 .BI if( list ) 450 .IR command . 451 If its condition was non-zero, the 452 .I command 453 is executed. 454 .HP 455 .BI for( name 456 .B in 457 .IB arguments ) 458 .I command 459 .HP 460 .BI for( name ) 461 .I command 462 .br 463 The 464 .I command 465 is executed once for each 466 .IR argument 467 with that argument assigned to 468 .IR name . 469 If the argument list is omitted, 470 .B $* 471 is used. 472 .HP 473 .BI while( list ) 474 .I command 475 .br 476 The 477 .I list 478 is executed repeatedly until its exit status is non-null. 479 Each time it returns null status, the 480 .I command 481 is executed. 482 An empty 483 .I list 484 is taken to give null status. 485 .HP 486 .BI "switch(" argument "){" list } 487 .br 488 The 489 .IR list 490 is searched for simple commands beginning with the word 491 .BR case . 492 (The search is only at the `top level' of the 493 .IR list . 494 That is, 495 .B cases 496 in nested constructs are not found.) 497 .I Argument 498 is matched against each word following 499 .B case 500 using the pattern-matching algorithm described above, except that 501 .B / 502 and the first characters of 503 .B . 504 and 505 .B .. 506 need not be matched explicitly. 507 When a match is found, commands in the list are executed up to the next 508 following 509 .B case 510 command (at the top level) or the closing brace. 511 .HP 512 .BI { list } 513 .br 514 Braces serve to alter the grouping of commands implied by operator 515 priorities. 516 The 517 .I body 518 is a sequence of commands separated by 519 .BR & , 520 .BR ; , 521 or newline. 522 .HP 523 .BI "fn " name { list } 524 .HP 525 .BI "fn " name 526 .br 527 The first form defines a function with the given 528 .IR name . 529 Subsequently, whenever a command whose first argument is 530 .I name 531 is encountered, the current value of 532 the remainder of the command's argument list will be assigned to 533 .BR $* , 534 after saving its current value, and 535 .I rc 536 will execute the 537 .IR list . 538 The second form removes 539 .IR name 's 540 function definition. 541 .HP 542 .BI "fn " note { list } 543 .br 544 .HP 545 .BI "fn " note 546 .br 547 A function with a special name will be called when 548 .I rc 549 receives a corresponding note; see 550 .IR notify (3). 551 The valid note names (and corresponding notes) are 552 .B sighup 553 .RB ( hangup ), 554 .B sigint 555 .RB ( interrupt ), 556 .BR sigalrm 557 .RB ( alarm ), 558 and 559 .B sigfpe 560 (floating point trap). 561 By default 562 .I rc 563 exits on receiving any signal, except when run interactively, 564 in which case interrupts and quits normally cause 565 .I rc 566 to stop whatever it's doing and start reading a new command. 567 The second form causes 568 .I rc 569 to handle a signal in the default manner. 570 .I Rc 571 recognizes an artificial note, 572 .BR sigexit , 573 which occurs when 574 .I rc 575 is about to finish executing. 576 .HP 577 .IB name = "argument command" 578 .br 579 Any command may be preceded by a sequence of assignments 580 interspersed with redirections. 581 The assignments remain in effect until the end of the command, unless 582 the command is empty (i.e. the assignments stand alone), in which case 583 they are effective until rescinded by later assignments. 584 .PD 585 .SS Built-in Commands 586 These commands are executed internally by 587 .IR rc , 588 usually because their execution changes or depends on 589 .IR rc 's 590 internal state. 591 .PD 0 592 .HP 593 .BI . " file ..." 594 .br 595 Execute commands from 596 .IR file . 597 .B $* 598 is set for the duration to the remainder of the argument list following 599 .IR file . 600 .I File 601 is searched for using 602 .BR $path . 603 .HP 604 .BI builtin " command ..." 605 .br 606 Execute 607 .I command 608 as usual except that any function named 609 .I command 610 is ignored in favor of the built-in meaning. 611 .HP 612 .BI "cd [" dir "]" 613 .br 614 Change the current directory to 615 .IR dir . 616 The default argument is 617 .BR $home . 618 .I dir 619 is searched for in each of the directories mentioned in 620 .BR $cdpath . 621 .HP 622 .BI "eval [" "arg ..." "]" 623 .br 624 The arguments are concatenated separated by spaces into a single string, 625 read as input to 626 .IR rc , 627 and executed. 628 .HP 629 .BI "exec [" "command ..." "]" 630 .br 631 This instance of 632 .I rc 633 replaces itself with the given (non-built-in) 634 .IR command . 635 .HP 636 .BI "flag " f " [+-]" 637 .br 638 Either set 639 .RB ( + ), 640 clear 641 .RB ( - ), 642 or test (neither 643 .B + 644 nor 645 .BR - ) 646 the flag 647 .IR f , 648 where 649 .I f 650 is a single character, one of the command line flags (see Invocation, below). 651 .HP 652 .BI "exit [" status "]" 653 .br 654 Exit with the given exit status. 655 If none is given, the current value of 656 .B $status 657 is used. 658 .HP 659 .BR "rfork " [ nNeEsfFm ] 660 .br 661 Become a new process group using 662 .BI rfork( flags ) 663 where 664 .I flags 665 is composed of the bitwise OR of the 666 .B rfork 667 flags specified by the option letters 668 (see 669 .IR fork (2)). 670 If no 671 .I flags 672 are given, they default to 673 .BR ens . 674 The 675 .I flags 676 and their meanings are: 677 .B n 678 is 679 .BR RFNAMEG ; 680 .B N 681 is 682 .BR RFCNAMEG ; 683 .B e 684 is 685 .BR RFENVG ; 686 .B E 687 is 688 .BR RFCENVG ; 689 .B s 690 is 691 .BR RFNOTEG ; 692 .B f 693 is 694 .BR RFFDG ; 695 .B F 696 is 697 .BR RFCFDG ; 698 and 699 .B m 700 is 701 .BR RFNOMNT . 702 .HP 703 .BI "shift [" n "]" 704 .br 705 Delete the first 706 .IR n 707 (default 1) 708 elements of 709 .BR $* . 710 .HP 711 .BI "wait [" pid "]" 712 .br 713 Wait for the process with the given 714 .I pid 715 to exit. 716 If no 717 .I pid 718 is given, all outstanding processes are waited for. 719 .HP 720 .BI whatis " name ..." 721 .br 722 Print the value of each 723 .I name 724 in a form suitable for input to 725 .IR rc . 726 The output is 727 an assignment to any variable, 728 the definition of any function, 729 a call to 730 .B builtin 731 for any built-in command, or 732 the completed pathname of any executable file. 733 .HP 734 .BI ~ " subject pattern ..." 735 .br 736 The 737 .I subject 738 is matched against each 739 .I pattern 740 in sequence. 741 If it matches any pattern, 742 .B $status 743 is set to zero. 744 Otherwise, 745 .B $status 746 is set to one. 747 Patterns are the same as for file name matching, except that 748 .B / 749 and the first character of 750 .B . 751 and 752 .B .. 753 need not be matched explicitly. 754 The 755 .I patterns 756 are not subjected to 757 file name matching before the 758 .B ~ 759 command is executed, so they need not be enclosed in quotation marks. 760 .PD 761 .SS Environment 762 The 763 .I environment 764 is a list of strings made available to executing binaries by the 765 kernel. 766 .I Rc 767 creates an environment entry for each variable whose value is non-empty, 768 and for each function. 769 The string for a variable entry has the variable's name followed by 770 .B = 771 and its value. 772 If the value has more than one component, these 773 are separated by SOH (001) 774 characters. 775 The string for a function is just the 776 .I rc 777 input that defines the function. 778 The name of a function in the environment is the function name 779 preceded by 780 .LR fn# . 781 .PP 782 When 783 .I rc 784 starts executing it reads variable and function definitions from its 785 environment. 786 .SS Special Variables 787 The following variables are set or used by 788 .IR rc . 789 .PD 0 790 .TP \w'\fL$promptXX'u 791 .B $* 792 Set to 793 .IR rc 's 794 argument list during initialization. 795 Whenever a 796 .B . 797 command or a function is executed, the current value is saved and 798 .B $* 799 receives the new argument list. 800 The saved value is restored on completion of the 801 .B . 802 or function. 803 .TP 804 .B $apid 805 Whenever a process is started asynchronously with 806 .BR & , 807 .B $apid 808 is set to its process id. 809 .TP 810 .B $home 811 The default directory for 812 .BR cd . 813 .TP 814 .B $ifs 815 The input field separators used in backquote substitutions. 816 If 817 .B $ifs 818 is not set in 819 .IR rc 's 820 environment, it is initialized to blank, tab and newline. 821 .TP 822 .B $path 823 The search path used to find commands and input files 824 for the 825 .B . 826 command. 827 If not set in the environment, it is initialized by 828 parsing the 829 .B $PATH 830 variable 831 (as in 832 .IR sh (1)) 833 or by 834 .BR "path=(.\ /bin)" . 835 The variables 836 .B $path 837 and 838 .B $PATH 839 are maintained together: changes to one will be reflected in the other. 840 .\" Its use is discouraged; instead use 841 .\" .IR bind (1) 842 .\" to build a 843 .\" .B /bin 844 .\" containing what's needed. 845 .TP 846 .B $pid 847 Set during initialization to 848 .IR rc 's 849 process id. 850 .TP 851 .B $prompt 852 When 853 .I rc 854 is run interactively, the first component of 855 .B $prompt 856 is printed before reading each command. 857 The second component is printed whenever a newline is typed and more lines 858 are required to complete the command. 859 If not set in the environment, it is initialized by 860 .BR "prompt=('%\ '\ '\ ')" . 861 .TP 862 .B $status 863 Set to the wait message of the last-executed program. 864 (unless started with 865 .BR &). 866 .B ! 867 and 868 .B ~ 869 also change 870 .BR $status . 871 Its value is used to control execution in 872 .BR && , 873 .BR || , 874 .B if 875 and 876 .B while 877 commands. 878 When 879 .I rc 880 exits at end-of-file of its input or on executing an 881 .B exit 882 command with no argument, 883 .B $status 884 is its exit status. 885 .PD 886 .SS Invocation 887 If 888 .I rc 889 is started with no arguments it reads commands from standard input. 890 Otherwise its first non-flag argument is the name of a file from which 891 to read commands (but see 892 .B -c 893 below). 894 Subsequent arguments become the initial value of 895 .BR $* . 896 .I Rc 897 accepts the following command-line flags. 898 .PD 0 899 .TP \w'\fL-c\ \fIstring\fLXX'u 900 .BI -c " string" 901 Commands are read from 902 .IR string . 903 .TP 904 .B -s 905 Print out exit status after any command where the status is non-null. 906 .TP 907 .B -e 908 Exit if 909 .B $status 910 is non-null after executing a simple command. 911 .TP 912 .B -i 913 If 914 .B -i 915 is present, or 916 .I rc 917 is given no arguments and its standard input is a terminal, 918 it runs interactively. 919 Commands are prompted for using 920 .BR $prompt . 921 .TP 922 .B -I 923 Makes sure 924 .I rc 925 is not run interactively. 926 .TP 927 .B -l 928 If 929 .B -l 930 is given or the first character of argument zero is 931 .BR - , 932 .I rc 933 reads commands from 934 .BR $home/lib/profile , 935 if it exists, before reading its normal input. 936 .TP 937 .B -p 938 A no-op. 939 .TP 940 .B -d 941 A no-op. 942 .TP 943 .B -v 944 Echo input on file descriptor 2 as it is read. 945 .TP 946 .B -x 947 Print each simple command before executing it. 948 .TP 949 .B -r 950 Print debugging information (internal form of commands 951 as they are executed). 952 .PD 953 .SH SOURCE 954 .B \*9/src/cmd/rc 955 .SH "SEE ALSO" 956 Tom Duff, 957 ``Rc \- The Plan 9 Shell''. 958 .SH BUGS 959 There should be a way to match patterns against whole lists rather than 960 just single strings. 961 .PP 962 Using 963 .B ~ 964 to check the value of 965 .B $status 966 changes 967 .BR $status . 968 .PP 969 Functions that use here documents don't work. 970 .PP 971 Free carets don't get inserted next to keywords. 972 .PP 973 The 974 .BI <{ command } 975 syntax depends on the underlying operating system 976 providing a file descriptor device tree at 977 .BR /dev/fd . 978 .PP 979 By default, FreeBSD 5 980 does not provide file descriptors greater than 2 981 in 982 .BR /dev/fd . 983 To fix this, add 984 .IP 985 .EX 986 /fdescfs /dev/fd fdescfs rw 0 0 987 .EE 988 .LP 989 to 990 .BR /etc/fstab , 991 and then 992 .B mount 993 .BR /dev/fd . 994 (Adding the line to 995 .B fstab 996 ensures causes FreeBSD to mount the file system 997 automatically at boot time.)