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| 32 | .\" @(#)csh.2 8.1 (Berkeley) 6/8/93 |
| 33 | .\" $FreeBSD: src/bin/csh/USD.doc/csh.2,v 1.7.2.1 2001/07/22 11:32:15 dd Exp $ |
| 34 | .\" $DragonFly: src/bin/csh/USD.doc/csh.2,v 1.2 2003/06/17 04:22:49 dillon Exp $ |
| 35 | .\" |
| 36 | .nr H1 1 |
| 37 | .NH |
| 38 | Details on the shell for terminal users |
| 39 | .NH 2 |
| 40 | Shell startup and termination |
| 41 | .PP |
| 42 | When you login, the shell is started by the system in your |
| 43 | .I home |
| 44 | directory and begins by reading commands from a file |
| 45 | .I \&.cshrc |
| 46 | in this directory. |
| 47 | All shells which you may start during your terminal session will |
| 48 | read from this file. |
| 49 | We will later see what kinds of commands are usefully placed there. |
| 50 | For now we need not have this file and the shell does not complain about |
| 51 | its absence. |
| 52 | .PP |
| 53 | A |
| 54 | .I "login shell" , |
| 55 | executed after you login to the system, |
| 56 | will, after it reads commands from |
| 57 | .I \&.cshrc, |
| 58 | read commands from a file |
| 59 | .I \&.login |
| 60 | also in your home directory. |
| 61 | This file contains commands which you wish to do each time you login |
| 62 | to the \s-2UNIX\s0 system. |
| 63 | My |
| 64 | .I \&.login |
| 65 | file looks something like: |
| 66 | .DS |
| 67 | set ignoreeof |
| 68 | set mail=(/usr/spool/mail/bill) |
| 69 | echo "${prompt}users" ; users |
| 70 | alias ts \e |
| 71 | \'set noglob ; eval \`tset \-s \-m dialup:c100rv4pna \-m plugboard:?hp2621nl \!*\`\'; |
| 72 | ts; stty intr ^C kill ^U crt |
| 73 | set time=15 history=10 |
| 74 | msgs \-f |
| 75 | if (\-e $mail) then |
| 76 | echo "${prompt}mail" |
| 77 | mail |
| 78 | endif |
| 79 | .DE |
| 80 | .PP |
| 81 | This file contains several commands to be executed by \s-2UNIX\s0 |
| 82 | each time I login. |
| 83 | The first is a |
| 84 | .I set |
| 85 | command which is interpreted directly by the shell. It sets the shell |
| 86 | variable |
| 87 | .I ignoreeof |
| 88 | which causes the shell to not log me off if I hit ^D. Rather, |
| 89 | I use the |
| 90 | .I logout |
| 91 | command to log off of the system. |
| 92 | By setting the |
| 93 | .I mail |
| 94 | variable, I ask the shell to watch for incoming mail to me. Every 5 minutes |
| 95 | the shell looks for this file and tells me if more mail has arrived there. |
| 96 | An alternative to this is to put the command |
| 97 | .DS |
| 98 | biff y |
| 99 | .DE |
| 100 | in place of this |
| 101 | .I set; |
| 102 | this will cause me to be notified immediately when mail arrives, and to |
| 103 | be shown the first few lines of the new message. |
| 104 | .PP |
| 105 | Next I set the shell variable `time' to `15' causing the shell to automatically |
| 106 | print out statistics lines for commands which execute for at least 15 seconds |
| 107 | of \s-2CPU\s+2 time. The variable `history' is set to 10 indicating that |
| 108 | I want the shell to remember the last 10 commands I type in its |
| 109 | .I "history list" , |
| 110 | (described later). |
| 111 | .PP |
| 112 | I create an |
| 113 | .I alias |
| 114 | ``ts'' which executes a |
| 115 | \fItset\fR\|(1) command setting up the modes of the terminal. |
| 116 | The parameters to |
| 117 | .I tset |
| 118 | indicate the kinds of terminal which I usually use when not on a hardwired |
| 119 | port. I then execute ``ts'' and also use the |
| 120 | .I stty |
| 121 | command to change the interrupt character to ^C and the line kill |
| 122 | character to ^U. |
| 123 | .PP |
| 124 | I then run the `msgs' program, which provides me with any |
| 125 | system messages which I have not seen before; the `\-f' option here prevents |
| 126 | it from telling me anything if there are no new messages. |
| 127 | Finally, if my mailbox file exists, then I run the `mail' program to |
| 128 | process my mail. |
| 129 | .PP |
| 130 | When the `mail' and `msgs' programs finish, the shell will finish |
| 131 | processing my |
| 132 | .I \&.login |
| 133 | file and begin reading commands from the terminal, prompting for each with |
| 134 | `% '. |
| 135 | When I log off (by giving the |
| 136 | .I logout |
| 137 | command) the shell |
| 138 | will print `logout' and execute commands from the file `.logout' |
| 139 | if it exists in my home directory. |
| 140 | After that the shell will terminate and \s-2UNIX\s0 will log |
| 141 | me off the system. |
| 142 | If the system is not going down, I will receive a new login message. |
| 143 | In any case, after the `logout' message the shell is committed to terminating |
| 144 | and will take no further input from my terminal. |
| 145 | .NH 2 |
| 146 | Shell variables |
| 147 | .PP |
| 148 | The shell maintains a set of |
| 149 | .I variables. |
| 150 | We saw above the variables |
| 151 | .I history |
| 152 | and |
| 153 | .I time |
| 154 | which had values `10' and `15'. |
| 155 | In fact, each shell variable has as value an array of |
| 156 | zero or more |
| 157 | .I strings. |
| 158 | Shell variables may be assigned values by the set command. It has |
| 159 | several forms, the most useful of which was given above and is |
| 160 | .DS |
| 161 | set name=value |
| 162 | .DE |
| 163 | .PP |
| 164 | Shell variables may be used to store values which are to |
| 165 | be used in commands later through a substitution mechanism. |
| 166 | The shell variables most commonly referenced are, however, those which the |
| 167 | shell itself refers to. |
| 168 | By changing the values of these variables one can directly affect the |
| 169 | behavior of the shell. |
| 170 | .PP |
| 171 | One of the most important variables is the variable |
| 172 | .I path. |
| 173 | This variable contains a sequence of directory names where the shell |
| 174 | searches for commands. |
| 175 | The |
| 176 | .I set |
| 177 | command with no arguments |
| 178 | shows the value of all variables currently defined (we usually say |
| 179 | .I set) |
| 180 | in the shell. |
| 181 | The default value for path will be shown by |
| 182 | .I set |
| 183 | to be |
| 184 | .DS |
| 185 | % set |
| 186 | .ta .75i |
| 187 | argv () |
| 188 | cwd /usr/bill |
| 189 | home /usr/bill |
| 190 | path (. /usr/ucb /bin /usr/bin) |
| 191 | prompt % |
| 192 | shell /bin/csh |
| 193 | status 0 |
| 194 | term c100rv4pna |
| 195 | user bill |
| 196 | % |
| 197 | .so tabs |
| 198 | .DE |
| 199 | This output indicates that the variable path points to the current |
| 200 | directory `.' and then `/usr/ucb', `/bin' and `/usr/bin'. |
| 201 | Commands which you may write might be in `.' (usually one of |
| 202 | your directories). |
| 203 | Commands developed at Berkeley, live in `/usr/ucb' |
| 204 | while commands developed at Bell Laboratories live in `/bin' and `/usr/bin'. |
| 205 | .PP |
| 206 | A number of locally developed programs on the system live in the directory |
| 207 | `/usr/local'. |
| 208 | If we wish that all shells which we invoke to have |
| 209 | access to these new programs we can place the command |
| 210 | .DS |
| 211 | set path=(. /usr/ucb /bin /usr/bin /usr/local) |
| 212 | .DE |
| 213 | in our file |
| 214 | .I \&.cshrc |
| 215 | in our home directory. |
| 216 | Try doing this and then logging out and back in and do |
| 217 | .DS |
| 218 | set |
| 219 | .DE |
| 220 | again to see that the value assigned to |
| 221 | .I path |
| 222 | has changed. |
| 223 | .FS \(dg |
| 224 | Another directory that might interest you is /usr/new, which contains |
| 225 | many useful user-contributed programs provided with Berkeley Unix. |
| 226 | .FE |
| 227 | .PP |
| 228 | One thing you should be aware of is that the shell examines each directory |
| 229 | which you insert into your path and determines which commands are contained |
| 230 | there. Except for the current directory `.', which the shell treats specially, |
| 231 | this means that if commands are added to a directory in your search path after |
| 232 | you have started the shell, they will not necessarily be found by the shell. |
| 233 | If you wish to use a command which has been added in this way, you should |
| 234 | give the command |
| 235 | .DS |
| 236 | rehash |
| 237 | .DE |
| 238 | to the shell, which will cause it to recompute its internal table of command |
| 239 | locations, so that it will find the newly added command. |
| 240 | Since the shell has to look in the current directory `.' on each command, |
| 241 | placing it at the end of the path specification usually works equivalently |
| 242 | and reduces overhead. |
| 243 | .PP |
| 244 | Other useful built in variables are the variable |
| 245 | .I home |
| 246 | which shows your home directory, |
| 247 | .I cwd |
| 248 | which contains your current working directory, |
| 249 | the variable |
| 250 | .I ignoreeof |
| 251 | which can be set in your |
| 252 | .I \&.login |
| 253 | file to tell the shell not to exit when it receives an end-of-file from |
| 254 | a terminal (as described above). |
| 255 | The variable `ignoreeof' |
| 256 | is one of several variables which the shell does not care about the |
| 257 | value of, only whether they are |
| 258 | .I set |
| 259 | or |
| 260 | .I unset. |
| 261 | Thus to set this variable you simply do |
| 262 | .DS |
| 263 | set ignoreeof |
| 264 | .DE |
| 265 | and to unset it do |
| 266 | .DS |
| 267 | unset ignoreeof |
| 268 | .DE |
| 269 | These give the variable `ignoreeof' no value, but none is desired or required. |
| 270 | .PP |
| 271 | Finally, some other built-in shell variables of use are the |
| 272 | variables |
| 273 | .I noclobber |
| 274 | and |
| 275 | .I mail. |
| 276 | The metasyntax |
| 277 | .DS |
| 278 | > filename |
| 279 | .DE |
| 280 | which redirects the standard output of a command |
| 281 | will overwrite and destroy the previous contents of the named file. |
| 282 | In this way you may accidentally overwrite a file which is valuable. |
| 283 | If you would prefer that the shell not overwrite files in this |
| 284 | way you can |
| 285 | .DS |
| 286 | set noclobber |
| 287 | .DE |
| 288 | in your |
| 289 | .I \&.login |
| 290 | file. |
| 291 | Then trying to do |
| 292 | .DS |
| 293 | date > now |
| 294 | .DE |
| 295 | would cause a diagnostic if `now' existed already. |
| 296 | You could type |
| 297 | .DS |
| 298 | date >! now |
| 299 | .DE |
| 300 | if you really wanted to overwrite the contents of `now'. |
| 301 | The `>!' is a special metasyntax indicating that clobbering the |
| 302 | file is ok.\(dg |
| 303 | .FS |
| 304 | \(dgThe space between the `!' and the word `now' is critical here, as `!now' |
| 305 | would be an invocation of the |
| 306 | .I history |
| 307 | mechanism, and have a totally different effect. |
| 308 | .FE |
| 309 | .NH 2 |
| 310 | The shell's history list |
| 311 | .PP |
| 312 | The shell can maintain a |
| 313 | .I "history list" |
| 314 | into which it places the words |
| 315 | of previous commands. |
| 316 | It is possible to use a notation to reuse commands or words |
| 317 | from commands in forming new commands. |
| 318 | This mechanism can be used to repeat previous commands or to |
| 319 | correct minor typing mistakes in commands. |
| 320 | .PP |
| 321 | The following figure gives a sample session involving typical usage of the |
| 322 | history mechanism of the shell. |
| 323 | .KF |
| 324 | .DS |
| 325 | % cat bug.c |
| 326 | main() |
| 327 | |
| 328 | { |
| 329 | printf("hello); |
| 330 | } |
| 331 | % cc !$ |
| 332 | cc bug.c |
| 333 | "bug.c", line 4: newline in string or char constant |
| 334 | "bug.c", line 5: syntax error |
| 335 | % ed !$ |
| 336 | ed bug.c |
| 337 | 29 |
| 338 | 4s/);/"&/p |
| 339 | printf("hello"); |
| 340 | w |
| 341 | 30 |
| 342 | q |
| 343 | % !c |
| 344 | cc bug.c |
| 345 | % a.out |
| 346 | hello% !e |
| 347 | ed bug.c |
| 348 | 30 |
| 349 | 4s/lo/lo\e\en/p |
| 350 | printf("hello\en"); |
| 351 | w |
| 352 | 32 |
| 353 | q |
| 354 | % !c \-o bug |
| 355 | cc bug.c \-o bug |
| 356 | % size a.out bug |
| 357 | a.out: 2784+364+1028 = 4176b = 0x1050b |
| 358 | bug: 2784+364+1028 = 4176b = 0x1050b |
| 359 | % ls \-l !* |
| 360 | ls \-l a.out bug |
| 361 | \(mirwxr\(mixr\(mix 1 bill 3932 Dec 19 09:41 a.out |
| 362 | \(mirwxr\(mixr\(mix 1 bill 3932 Dec 19 09:42 bug |
| 363 | % bug |
| 364 | hello |
| 365 | % num bug.c | spp |
| 366 | spp: Command not found. |
| 367 | % ^spp^ssp |
| 368 | num bug.c | ssp |
| 369 | 1 main() |
| 370 | 3 { |
| 371 | 4 printf("hello\en"); |
| 372 | 5 } |
| 373 | % !! | lpr |
| 374 | num bug.c | ssp | lpr |
| 375 | % |
| 376 | .DE |
| 377 | .KE |
| 378 | In this example we have a very simple C program which has a bug (or two) |
| 379 | in it in the file `bug.c', which we `cat' out on our terminal. We then |
| 380 | try to run the C compiler on it, referring to the file again as `!$', |
| 381 | meaning the last argument to the previous command. Here the `!' is the |
| 382 | history mechanism invocation metacharacter, and the `$' stands for the last |
| 383 | argument, by analogy to `$' in the editor which stands for the end of the line. |
| 384 | The shell echoed the command, as it would have been typed without use of |
| 385 | the history mechanism, and then executed it. |
| 386 | The compilation yielded error diagnostics so we now run the editor on the |
| 387 | file we were trying to compile, fix the bug, and run the C compiler again, |
| 388 | this time referring to this command simply as `!c', which repeats the last |
| 389 | command which started with the letter `c'. If there were other |
| 390 | commands starting with `c' done recently we could have said `!cc' or even |
| 391 | `!cc:p' which would have printed the last command starting with `cc' |
| 392 | without executing it. |
| 393 | .PP |
| 394 | After this recompilation, we ran the resulting `a.out' file, and then |
| 395 | noting that there still was a bug, ran the editor again. After fixing |
| 396 | the program we ran the C compiler again, but tacked onto the command |
| 397 | an extra `\-o bug' telling the compiler to place the resultant binary in |
| 398 | the file `bug' rather than `a.out'. In general, the history mechanisms |
| 399 | may be used anywhere in the formation of new commands and other characters |
| 400 | may be placed before and after the substituted commands. |
| 401 | .PP |
| 402 | We then ran the `size' command to see how large the binary program images |
| 403 | we have created were, and then an `ls \-l' command with the same argument |
| 404 | list, denoting the argument list `\!*'. |
| 405 | Finally we ran the program `bug' to see that its output is indeed correct. |
| 406 | .PP |
| 407 | To make a numbered listing of the program we ran the `num' command on the file `bug.c'. |
| 408 | In order to compress out blank lines in the output of `num' we ran the |
| 409 | output through the filter `ssp', but misspelled it as spp. To correct this |
| 410 | we used a shell substitute, placing the old text and new text between `^' |
| 411 | characters. This is similar to the substitute command in the editor. |
| 412 | Finally, we repeated the same command with `!!', but sent its output to the |
| 413 | line printer. |
| 414 | .PP |
| 415 | There are other mechanisms available for repeating commands. The |
| 416 | .I history |
| 417 | command prints out a number of previous commands with numbers by which |
| 418 | they can be referenced. There is a way to refer to a previous command |
| 419 | by searching for a string which appeared in it, and there are other, |
| 420 | less useful, ways to select arguments to include in a new command. |
| 421 | A complete description of all these mechanisms |
| 422 | is given in the C shell manual pages in the \s-2UNIX\s0 Programmer's Manual. |
| 423 | .NH 2 |
| 424 | Aliases |
| 425 | .PP |
| 426 | The shell has an |
| 427 | .I alias |
| 428 | mechanism which can be used to make transformations on input commands. |
| 429 | This mechanism can be used to simplify the commands you type, |
| 430 | to supply default arguments to commands, |
| 431 | or to perform transformations on commands and their arguments. |
| 432 | The alias facility is similar to a macro facility. |
| 433 | Some of the features obtained by aliasing can be obtained also |
| 434 | using shell command files, but these take place in another instance |
| 435 | of the shell and cannot directly affect the current shells environment |
| 436 | or involve commands such as |
| 437 | .I cd |
| 438 | which must be done in the current shell. |
| 439 | .PP |
| 440 | As an example, suppose that there is a new version of the mail program |
| 441 | on the system called `newmail' |
| 442 | you wish to use, rather than the standard mail program which is called |
| 443 | `mail'. |
| 444 | If you place the shell command |
| 445 | .DS |
| 446 | alias mail newmail |
| 447 | .DE |
| 448 | in your |
| 449 | .I \&.cshrc |
| 450 | file, the shell will transform an input line of the form |
| 451 | .DS |
| 452 | mail bill |
| 453 | .DE |
| 454 | into a call on `newmail'. |
| 455 | More generally, suppose we wish the command `ls' to always show |
| 456 | sizes of files, that is to always do `\-s'. |
| 457 | We can do |
| 458 | .DS |
| 459 | alias ls ls \-s |
| 460 | .DE |
| 461 | or even |
| 462 | .DS |
| 463 | alias dir ls \-s |
| 464 | .DE |
| 465 | creating a new command syntax `dir' |
| 466 | which does an `ls \-s'. |
| 467 | If we say |
| 468 | .DS |
| 469 | dir ~bill |
| 470 | .DE |
| 471 | then the shell will translate this to |
| 472 | .DS |
| 473 | ls \-s /mnt/bill |
| 474 | .DE |
| 475 | .PP |
| 476 | Thus the |
| 477 | .I alias |
| 478 | mechanism can be used to provide short names for commands, |
| 479 | to provide default arguments, |
| 480 | and to define new short commands in terms of other commands. |
| 481 | It is also possible to define aliases which contain multiple |
| 482 | commands or pipelines, showing where the arguments to the original |
| 483 | command are to be substituted using the facilities of the |
| 484 | history mechanism. |
| 485 | Thus the definition |
| 486 | .DS |
| 487 | alias cd \'cd \e!* ; ls \' |
| 488 | .DE |
| 489 | would do an |
| 490 | .I ls |
| 491 | command after each change directory |
| 492 | .I cd |
| 493 | command. |
| 494 | We enclosed the entire alias definition in `\'' characters to prevent |
| 495 | most substitutions from occurring and the character `;' from being |
| 496 | recognized as a metacharacter. |
| 497 | The `!' here is escaped with a `\e' to prevent it from being interpreted |
| 498 | when the alias command is typed in. |
| 499 | The `\e!*' here substitutes the entire argument list to the pre-aliasing |
| 500 | .I cd |
| 501 | command, without giving an error if there were no arguments. |
| 502 | The `;' separating commands is used here |
| 503 | to indicate that one command is to be done and then the next. |
| 504 | Similarly the definition |
| 505 | .DS |
| 506 | alias whois \'grep \e!^ /etc/passwd\' |
| 507 | .DE |
| 508 | defines a command which looks up its first argument in the password file. |
| 509 | .PP |
| 510 | .B Warning: |
| 511 | The shell currently reads the |
| 512 | .I \&.cshrc |
| 513 | file each time it starts up. If you place a large number of commands |
| 514 | there, shells will tend to start slowly. A mechanism for saving the shell |
| 515 | environment after reading the \fI\&.cshrc\fR file and quickly restoring it is |
| 516 | under development, but for now you should try to limit the number of |
| 517 | aliases you have to a reasonable number... 10 or 15 is reasonable, |
| 518 | 50 or 60 will cause a noticeable delay in starting up shells, and make |
| 519 | the system seem sluggish when you execute commands from within the editor |
| 520 | and other programs. |
| 521 | .NH 2 |
| 522 | More redirection; >> and >& |
| 523 | .PP |
| 524 | There are a few more notations useful to the terminal user |
| 525 | which have not been introduced yet. |
| 526 | .PP |
| 527 | In addition to the standard output, commands also have a |
| 528 | .I "diagnostic output" |
| 529 | which is normally directed to the terminal even when the standard output |
| 530 | is redirected to a file or a pipe. |
| 531 | It is occasionally desirable to direct the diagnostic output along with |
| 532 | the standard output. |
| 533 | For instance if you want to redirect the output of a long running command |
| 534 | into a file and wish to have a record of any error diagnostic it produces |
| 535 | you can do |
| 536 | .DS |
| 537 | command >& file |
| 538 | .DE |
| 539 | The `>&' here tells the shell to route both the diagnostic output and the |
| 540 | standard output into `file'. |
| 541 | Similarly you can give the command |
| 542 | .DS |
| 543 | command |\|& lpr |
| 544 | .DE |
| 545 | to route both standard and diagnostic output through the pipe |
| 546 | to the line printer daemon |
| 547 | .I lpr.\(dd |
| 548 | .FS |
| 549 | \(dd A command of the form |
| 550 | .br |
| 551 | .ti +5 |
| 552 | command >&! file |
| 553 | .br |
| 554 | exists, and is used when |
| 555 | .I noclobber |
| 556 | is set and |
| 557 | .I file |
| 558 | already exists. |
| 559 | .FE |
| 560 | .PP |
| 561 | Finally, it is possible to use the form |
| 562 | .DS |
| 563 | command >> file |
| 564 | .DE |
| 565 | to place output at the end of an existing file.\(dg |
| 566 | .FS |
| 567 | \(dg If |
| 568 | .I noclobber |
| 569 | is set, then an error will result if |
| 570 | .I file |
| 571 | does not exist, otherwise the shell will create |
| 572 | .I file |
| 573 | if it doesn't exist. |
| 574 | A form |
| 575 | .br |
| 576 | .ti +5 |
| 577 | command >>! file |
| 578 | .br |
| 579 | makes it not be an error for file to not exist when |
| 580 | .I noclobber |
| 581 | is set. |
| 582 | .FE |
| 583 | .NH 2 |
| 584 | Jobs; Background, Foreground, or Suspended |
| 585 | .PP |
| 586 | When one or more commands |
| 587 | are typed together as a pipeline or as a sequence of commands separated by |
| 588 | semicolons, a single |
| 589 | .I job |
| 590 | is created by the shell consisting of these commands together as a unit. |
| 591 | Single commands without pipes or semicolons create the simplest jobs. |
| 592 | Usually, every line typed to the shell creates a job. |
| 593 | Some lines that create jobs (one per line) are |
| 594 | .DS |
| 595 | sort < data |
| 596 | ls \-s | sort \-n | head \-5 |
| 597 | mail harold |
| 598 | .DE |
| 599 | .PP |
| 600 | If the metacharacter `&' is typed |
| 601 | at the end of the commands, then the job is started as a |
| 602 | .I background |
| 603 | job. This means that the shell does not wait for it to complete but |
| 604 | immediately prompts and is ready for another command. The job runs |
| 605 | .I "in the background" |
| 606 | at the same time that normal jobs, called |
| 607 | .I foreground |
| 608 | jobs, continue to be read and executed by the shell one at a time. |
| 609 | Thus |
| 610 | .DS |
| 611 | du > usage & |
| 612 | .DE |
| 613 | would run the |
| 614 | .I du |
| 615 | program, which reports on the disk usage of your working directory (as well as |
| 616 | any directories below it), put the output into the file `usage' and return |
| 617 | immediately with a prompt for the next command without out waiting for |
| 618 | .I du |
| 619 | to finish. The |
| 620 | .I du |
| 621 | program would continue executing in the background |
| 622 | until it finished, even though you can type and execute more commands in the |
| 623 | mean time. |
| 624 | When a background |
| 625 | job terminates, a message is typed by the shell just before the next prompt |
| 626 | telling you that the job has completed. |
| 627 | In the following example the |
| 628 | .I du |
| 629 | job finishes sometime during the |
| 630 | execution of the |
| 631 | .I mail |
| 632 | command and its completion is reported just before |
| 633 | the prompt after the |
| 634 | .I mail |
| 635 | job is finished. |
| 636 | .DS |
| 637 | % du > usage & |
| 638 | [1] 503 |
| 639 | % mail bill |
| 640 | How do you know when a background job is finished? |
| 641 | EOT |
| 642 | .ta 1.75i |
| 643 | [1] \- Done du > usage |
| 644 | % |
| 645 | .so tabs |
| 646 | .DE |
| 647 | If the job did not terminate normally the `Done' message might say |
| 648 | something else like `Killed'. |
| 649 | If you want the |
| 650 | terminations of background jobs to be reported at the time they occur |
| 651 | (possibly interrupting the output of other foreground jobs), you can set |
| 652 | the |
| 653 | .I notify |
| 654 | variable. In the previous example this would mean that the |
| 655 | `Done' message might have come right in the middle of the message to |
| 656 | Bill. |
| 657 | Background jobs are unaffected by any signals from the keyboard like |
| 658 | the \s-2STOP\s0, \s-2INTERRUPT\s0, or \s-2QUIT\s0 signals mentioned earlier. |
| 659 | .PP |
| 660 | Jobs are recorded in a table inside the shell until they terminate. |
| 661 | In this table, the shell remembers the command names, arguments and the |
| 662 | .I "process numbers" |
| 663 | of all commands in the job as well as the working directory where the job was |
| 664 | started. |
| 665 | Each job in the table is either running |
| 666 | .I "in the foreground" |
| 667 | with the shell waiting for it to terminate, running |
| 668 | .I "in the background," |
| 669 | or |
| 670 | .I suspended. |
| 671 | Only one job can be running in the foreground at one time, but several |
| 672 | jobs can be suspended or running in the background at once. As each job |
| 673 | is started, it is assigned a small identifying |
| 674 | number called the |
| 675 | .I "job number" |
| 676 | which can be used later to refer to the job in the commands described below. |
| 677 | Job numbers remain |
| 678 | the same until the job terminates and then are re-used. |
| 679 | .PP |
| 680 | When a job is started in the backgound using `&', its number, as well |
| 681 | as the process numbers of all its (top level) commands, is typed by the shell |
| 682 | before prompting you for another command. |
| 683 | For example, |
| 684 | .DS |
| 685 | % ls \-s | sort \-n > usage & |
| 686 | [2] 2034 2035 |
| 687 | % |
| 688 | .DE |
| 689 | runs the `ls' program with the `\-s' options, pipes this output into |
| 690 | the `sort' program with the `\-n' option which puts its output into the |
| 691 | file `usage'. |
| 692 | Since the `&' was at the end of the line, these two programs were started |
| 693 | together as a background job. After starting the job, the shell prints |
| 694 | the job number in brackets (2 in this case) followed by the process number |
| 695 | of each program started in the job. Then the shell immediates prompts for |
| 696 | a new command, leaving the job running simultaneously. |
| 697 | .PP |
| 698 | As mentioned in section 1.8, foreground jobs become |
| 699 | .I suspended |
| 700 | by typing ^Z |
| 701 | which sends a \s-2STOP\s0 signal to the currently running |
| 702 | foreground job. A background job can become suspended by using the |
| 703 | .I stop |
| 704 | command described below. When jobs are suspended they merely stop |
| 705 | any further progress until started again, either in the foreground |
| 706 | or the backgound. The shell notices when a job becomes stopped and |
| 707 | reports this fact, much like it reports the termination of background jobs. |
| 708 | For foreground jobs this looks like |
| 709 | .DS |
| 710 | % du > usage |
| 711 | ^Z |
| 712 | Stopped |
| 713 | % |
| 714 | .DE |
| 715 | `Stopped' message is typed by the shell when it notices that the |
| 716 | .I du |
| 717 | program stopped. |
| 718 | For background jobs, using the |
| 719 | .I stop |
| 720 | command, it is |
| 721 | .DS |
| 722 | % sort usage & |
| 723 | [1] 2345 |
| 724 | % stop %1 |
| 725 | .ta 1.75i |
| 726 | [1] + Stopped (signal) sort usage |
| 727 | % |
| 728 | .so tabs |
| 729 | .DE |
| 730 | Suspending foreground jobs can be very useful when you need to temporarily |
| 731 | change what you are doing (execute other commands) and then return to |
| 732 | the suspended job. Also, foreground jobs can be suspended and then |
| 733 | continued as background jobs using the |
| 734 | .I bg |
| 735 | command, allowing you to continue other work and |
| 736 | stop waiting for the foreground job to finish. Thus |
| 737 | .DS |
| 738 | % du > usage |
| 739 | ^Z |
| 740 | Stopped |
| 741 | % bg |
| 742 | [1] du > usage & |
| 743 | % |
| 744 | .DE |
| 745 | starts `du' in the foreground, stops it before it finishes, then continues |
| 746 | it in the background allowing more foreground commands to be executed. |
| 747 | This is especially helpful |
| 748 | when a foreground job ends up taking longer than you expected and you |
| 749 | wish you had started it in the backgound in the beginning. |
| 750 | .PP |
| 751 | All |
| 752 | .I "job control" |
| 753 | commands can take an argument that identifies a particular |
| 754 | job. |
| 755 | All job name arguments begin with the character `%', since some of the |
| 756 | job control commands also accept process numbers (printed by the |
| 757 | .I ps |
| 758 | command.) |
| 759 | The default job (when no argument is given) is called the |
| 760 | .I current |
| 761 | job and is identified by a `+' in the output of the |
| 762 | .I jobs |
| 763 | command, which shows you which jobs you have. |
| 764 | When only one job is stopped or running in the background (the usual case) |
| 765 | it is always the current job thus no argument is needed. |
| 766 | If a job is stopped while running in the foreground it becomes the |
| 767 | .I current |
| 768 | job and the existing current job becomes the |
| 769 | .I previous |
| 770 | job \- identified by a `\-' in the output of |
| 771 | .I jobs. |
| 772 | When the current job terminates, the previous job becomes the current job. |
| 773 | When given, the argument is either `%\-' (indicating |
| 774 | the previous job); `%#', where # is the job number; |
| 775 | `%pref' where pref is some unique prefix of the command name |
| 776 | and arguments of one of the jobs; or `%?' followed by some string found |
| 777 | in only one of the jobs. |
| 778 | .PP |
| 779 | The |
| 780 | .I jobs |
| 781 | command types the table of jobs, giving the job number, |
| 782 | commands and status (`Stopped' or `Running') of each backgound or |
| 783 | suspended job. With the `\-l' option the process numbers are also |
| 784 | typed. |
| 785 | .DS |
| 786 | % du > usage & |
| 787 | [1] 3398 |
| 788 | % ls \-s | sort \-n > myfile & |
| 789 | [2] 3405 |
| 790 | % mail bill |
| 791 | ^Z |
| 792 | Stopped |
| 793 | % jobs |
| 794 | .ta 1.75i |
| 795 | [1] \(mi Running du > usage |
| 796 | [2] Running ls \-s | sort \-n > myfile |
| 797 | [3] \(pl Stopped mail bill |
| 798 | % fg %ls |
| 799 | ls \-s | sort \-n > myfile |
| 800 | % more myfile |
| 801 | .so tabs |
| 802 | .DE |
| 803 | .PP |
| 804 | The |
| 805 | .I fg |
| 806 | command runs a suspended or background job in the foreground. It is |
| 807 | used to restart a previously suspended job or change a background job |
| 808 | to run in the foreground (allowing signals or input from the terminal). |
| 809 | In the above example we used |
| 810 | .I fg |
| 811 | to change the `ls' job from the |
| 812 | background to the foreground since we wanted to wait for it to |
| 813 | finish before looking at its output file. |
| 814 | The |
| 815 | .I bg |
| 816 | command runs a suspended job in the background. It is usually used |
| 817 | after stopping the currently running foreground job with the |
| 818 | \s-2STOP\s0 signal. The combination of the \s-2STOP\s0 signal and the |
| 819 | .I bg |
| 820 | command changes a foreground job into a background job. |
| 821 | The |
| 822 | .I stop |
| 823 | command suspends a background job. |
| 824 | .PP |
| 825 | The |
| 826 | .I kill |
| 827 | command terminates a background or suspended job immediately. |
| 828 | In addition to jobs, it may be given process numbers as arguments, |
| 829 | as printed by |
| 830 | .I ps. |
| 831 | Thus, in the example above, the running |
| 832 | .I du |
| 833 | command could have been terminated by the command |
| 834 | .DS |
| 835 | % kill %1 |
| 836 | .ta 1.75i |
| 837 | [1] Terminated du > usage |
| 838 | % |
| 839 | .so tabs |
| 840 | .DE |
| 841 | .PP |
| 842 | The |
| 843 | .I notify |
| 844 | command (not the variable mentioned earlier) indicates that the termination |
| 845 | of a specific job should be |
| 846 | reported at the time it finishes instead of waiting for the next prompt. |
| 847 | .PP |
| 848 | If a job running in the background tries to read input from the terminal |
| 849 | it is automatically stopped. When such a job is then run in the |
| 850 | foreground, input can be given to the job. If desired, the job can |
| 851 | be run in the background again until it requests input again. |
| 852 | This is illustrated in the following sequence where the `s' command in the |
| 853 | text editor might take a long time. |
| 854 | .ID |
| 855 | .nf |
| 856 | % ed bigfile |
| 857 | 120000 |
| 858 | 1,$s/thisword/thatword/ |
| 859 | ^Z |
| 860 | Stopped |
| 861 | % bg |
| 862 | [1] ed bigfile & |
| 863 | % |
| 864 | . . . some foreground commands |
| 865 | .ta 1.75i |
| 866 | [1] Stopped (tty input) ed bigfile |
| 867 | % fg |
| 868 | ed bigfile |
| 869 | w |
| 870 | 120000 |
| 871 | q |
| 872 | % |
| 873 | .so tabs |
| 874 | .DE |
| 875 | So after the `s' command was issued, the `ed' job was stopped with ^Z |
| 876 | and then put in the background using |
| 877 | .I bg. |
| 878 | Some time later when the `s' command was finished, |
| 879 | .I ed |
| 880 | tried to read another command and was stopped because jobs |
| 881 | in the backgound cannot read from the terminal. The |
| 882 | .I fg |
| 883 | command returned the `ed' job to the foreground where it could once again |
| 884 | accept commands from the terminal. |
| 885 | .PP |
| 886 | The command |
| 887 | .DS |
| 888 | stty tostop |
| 889 | .DE |
| 890 | causes all background jobs run on your terminal to stop |
| 891 | when they are about to |
| 892 | write output to the terminal. This prevents messages from background |
| 893 | jobs from interrupting foreground job output and allows you to run |
| 894 | a job in the background without losing terminal output. It also |
| 895 | can be used for interactive programs that sometimes have long |
| 896 | periods without interaction. Thus each time it outputs a prompt for more |
| 897 | input it will stop before the prompt. It can then be run in the |
| 898 | foreground using |
| 899 | .I fg, |
| 900 | more input can be given and, if necessary stopped and returned to |
| 901 | the background. This |
| 902 | .I stty |
| 903 | command might be a good thing to put in your |
| 904 | .I \&.login |
| 905 | file if you do not like output from background jobs interrupting |
| 906 | your work. It also can reduce the need for redirecting the output |
| 907 | of background jobs if the output is not very big: |
| 908 | .DS |
| 909 | % stty tostop |
| 910 | % wc hugefile & |
| 911 | [1] 10387 |
| 912 | % ed text |
| 913 | \&. . . some time later |
| 914 | q |
| 915 | .ta 1.75i |
| 916 | [1] Stopped (tty output) wc hugefile |
| 917 | % fg wc |
| 918 | wc hugefile |
| 919 | 13371 30123 302577 |
| 920 | % stty \-tostop |
| 921 | .so tabs |
| 922 | .DE |
| 923 | Thus after some time the `wc' command, which counts the lines, words |
| 924 | and characters in a file, had one line of output. When it tried to |
| 925 | write this to the terminal it stopped. By restarting it in the |
| 926 | foreground we allowed it to write on the terminal exactly when we were |
| 927 | ready to look at its output. |
| 928 | Programs which attempt to change the mode of the terminal will also |
| 929 | block, whether or not |
| 930 | .I tostop |
| 931 | is set, when they are not in the foreground, as |
| 932 | it would be very unpleasant to have a background job change the state |
| 933 | of the terminal. |
| 934 | .PP |
| 935 | Since the |
| 936 | .I jobs |
| 937 | command only prints jobs started in the currently executing shell, |
| 938 | it knows nothing about background jobs started in other login sessions |
| 939 | or within shell files. The |
| 940 | .I ps |
| 941 | can be used in this case to find out about background jobs not started |
| 942 | in the current shell. |
| 943 | .NH 2 |
| 944 | Working Directories |
| 945 | .PP |
| 946 | As mentioned in section 1.6, the shell is always in a particular |
| 947 | .I "working directory." |
| 948 | The `change directory' command |
| 949 | .I chdir |
| 950 | (its |
| 951 | short form |
| 952 | .I cd |
| 953 | may also be used) |
| 954 | changes the working directory of the shell, |
| 955 | that is, changes the directory you |
| 956 | are located in. |
| 957 | .PP |
| 958 | It is useful to make a directory for each project you wish to work on |
| 959 | and to place all files related to that project in that directory. |
| 960 | The `make directory' command, |
| 961 | .I mkdir, |
| 962 | creates a new directory. |
| 963 | The |
| 964 | .I pwd |
| 965 | (`print working directory') command |
| 966 | reports the absolute pathname of the working directory of the shell, |
| 967 | that is, the directory you are |
| 968 | located in. |
| 969 | Thus in the example below: |
| 970 | .DS |
| 971 | % pwd |
| 972 | /usr/bill |
| 973 | % mkdir newpaper |
| 974 | % chdir newpaper |
| 975 | % pwd |
| 976 | /usr/bill/newpaper |
| 977 | % |
| 978 | .DE |
| 979 | the user has created and moved to the |
| 980 | directory |
| 981 | .I newpaper. |
| 982 | where, for example, he might |
| 983 | place a group of related files. |
| 984 | .PP |
| 985 | No matter where you have moved to in a directory hierarchy, |
| 986 | you can return to your `home' login directory by doing just |
| 987 | .DS |
| 988 | cd |
| 989 | .DE |
| 990 | with no arguments. |
| 991 | The name `..' always means the directory above the current one in |
| 992 | the hierarchy, thus |
| 993 | .DS |
| 994 | cd .. |
| 995 | .DE |
| 996 | changes the shell's working directory to the one directly above the |
| 997 | current one. |
| 998 | The name `..' can be used in any |
| 999 | pathname, thus, |
| 1000 | .DS |
| 1001 | cd ../programs |
| 1002 | .DE |
| 1003 | means |
| 1004 | change to the directory `programs' contained in the directory |
| 1005 | above the current one. |
| 1006 | If you have several directories for different |
| 1007 | projects under, say, your home directory, |
| 1008 | this shorthand notation |
| 1009 | permits you to switch easily between them. |
| 1010 | .PP |
| 1011 | The shell always remembers the pathname of its current working directory in |
| 1012 | the variable |
| 1013 | .I cwd. |
| 1014 | The shell can also be requested to remember the previous directory when |
| 1015 | you change to a new working directory. If the `push directory' command |
| 1016 | .I pushd |
| 1017 | is used in place of the |
| 1018 | .I cd |
| 1019 | command, the shell saves the name of the current working directory |
| 1020 | on a |
| 1021 | .I "directory stack" |
| 1022 | before changing to the new one. |
| 1023 | You can see this list at any time by typing the `directories' |
| 1024 | command |
| 1025 | .I dirs. |
| 1026 | .ID |
| 1027 | .nf |
| 1028 | % pushd newpaper/references |
| 1029 | ~/newpaper/references ~ |
| 1030 | % pushd /usr/lib/tmac |
| 1031 | /usr/lib/tmac ~/newpaper/references ~ |
| 1032 | % dirs |
| 1033 | /usr/lib/tmac ~/newpaper/references ~ |
| 1034 | % popd |
| 1035 | ~/newpaper/references ~ |
| 1036 | % popd |
| 1037 | ~ |
| 1038 | % |
| 1039 | .DE |
| 1040 | The list is printed in a horizontal line, reading left to right, |
| 1041 | with a tilde (~) as |
| 1042 | shorthand for your home directory\(emin this case `/usr/bill'. |
| 1043 | The directory stack is printed whenever there is more than one |
| 1044 | entry on it and it changes. |
| 1045 | It is also printed by a |
| 1046 | .I dirs |
| 1047 | command. |
| 1048 | .I Dirs |
| 1049 | is usually faster and more informative than |
| 1050 | .I pwd |
| 1051 | since it shows the current working directory as well as any |
| 1052 | other directories remembered in the stack. |
| 1053 | .PP |
| 1054 | The |
| 1055 | .I pushd |
| 1056 | command with no argument |
| 1057 | alternates the current directory with the first directory in the |
| 1058 | list. |
| 1059 | The `pop directory' |
| 1060 | .I popd |
| 1061 | command without an argument returns you to the directory you were in prior to |
| 1062 | the current one, discarding the previous current directory from the |
| 1063 | stack (forgetting it). |
| 1064 | Typing |
| 1065 | .I popd |
| 1066 | several times in a series takes you backward through the directories |
| 1067 | you had been in (changed to) by |
| 1068 | .I pushd |
| 1069 | command. |
| 1070 | There are other options to |
| 1071 | .I pushd |
| 1072 | and |
| 1073 | .I popd |
| 1074 | to manipulate the contents of the directory stack and to change |
| 1075 | to directories not at the top of the stack; see the |
| 1076 | .I csh |
| 1077 | manual page for details. |
| 1078 | .PP |
| 1079 | Since the shell remembers the working directory in which each job |
| 1080 | was started, it warns you when you might be confused by restarting |
| 1081 | a job in the foreground which has a different working directory than the |
| 1082 | current working directory of the shell. Thus if you start a background |
| 1083 | job, then change the shell's working directory and then cause the |
| 1084 | background job to run in the foreground, the shell warns you that the |
| 1085 | working directory of the currently running foreground job is different |
| 1086 | from that of the shell. |
| 1087 | .DS |
| 1088 | % dirs \-l |
| 1089 | /mnt/bill |
| 1090 | % cd myproject |
| 1091 | % dirs |
| 1092 | ~/myproject |
| 1093 | % ed prog.c |
| 1094 | 1143 |
| 1095 | ^Z |
| 1096 | Stopped |
| 1097 | % cd .. |
| 1098 | % ls |
| 1099 | myproject |
| 1100 | textfile |
| 1101 | % fg |
| 1102 | ed prog.c (wd: ~/myproject) |
| 1103 | .DE |
| 1104 | This way the shell warns you when there |
| 1105 | is an implied change of working directory, even though no cd command was |
| 1106 | issued. In the above example the `ed' job was still in `/mnt/bill/project' |
| 1107 | even though the shell had changed to `/mnt/bill'. |
| 1108 | A similar warning is given when such a foreground job |
| 1109 | terminates or is suspended (using the \s-2STOP\s0 signal) since |
| 1110 | the return to the shell again implies a change of working directory. |
| 1111 | .DS |
| 1112 | % fg |
| 1113 | ed prog.c (wd: ~/myproject) |
| 1114 | . . . after some editing |
| 1115 | q |
| 1116 | (wd now: ~) |
| 1117 | % |
| 1118 | .DE |
| 1119 | These messages are sometimes confusing if you use programs that change |
| 1120 | their own working directories, since the shell only remembers which |
| 1121 | directory a job is started in, and assumes it stays there. |
| 1122 | The `\-l' option of |
| 1123 | .I jobs |
| 1124 | will type the working directory |
| 1125 | of suspended or background jobs when it is different |
| 1126 | from the current working directory of the shell. |
| 1127 | .NH 2 |
| 1128 | Useful built-in commands |
| 1129 | .PP |
| 1130 | We now give a few of the useful built-in commands of the shell describing |
| 1131 | how they are used. |
| 1132 | .PP |
| 1133 | The |
| 1134 | .I alias |
| 1135 | command described above is used to assign new aliases and to show the |
| 1136 | existing aliases. |
| 1137 | With no arguments it prints the current aliases. |
| 1138 | It may also be given only one argument such as |
| 1139 | .DS |
| 1140 | alias ls |
| 1141 | .DE |
| 1142 | to show the current alias for, e.g., `ls'. |
| 1143 | .PP |
| 1144 | The |
| 1145 | .I echo |
| 1146 | command prints its arguments. |
| 1147 | It is often used in |
| 1148 | .I "shell scripts" |
| 1149 | or as an interactive command |
| 1150 | to see what filename expansions will produce. |
| 1151 | .PP |
| 1152 | The |
| 1153 | .I history |
| 1154 | command will show the contents of the history list. |
| 1155 | The numbers given with the history events can be used to reference |
| 1156 | previous events which are difficult to reference using the |
| 1157 | contextual mechanisms introduced above. |
| 1158 | There is also a shell variable called |
| 1159 | .I prompt. |
| 1160 | By placing a `!' character in its value the shell will there substitute |
| 1161 | the number of the current command in the history list. |
| 1162 | You can use this number to refer to this command in a history substitution. |
| 1163 | Thus you could |
| 1164 | .DS |
| 1165 | set prompt=\'\e! % \' |
| 1166 | .DE |
| 1167 | Note that the `!' character had to be |
| 1168 | .I escaped |
| 1169 | here even within `\'' characters. |
| 1170 | .PP |
| 1171 | The |
| 1172 | .I limit |
| 1173 | command is used to restrict use of resources. |
| 1174 | With no arguments it prints the current limitations: |
| 1175 | .DS |
| 1176 | .ta 1i |
| 1177 | cputime unlimited |
| 1178 | filesize unlimited |
| 1179 | datasize 5616 kbytes |
| 1180 | stacksize 512 kbytes |
| 1181 | coredumpsize unlimited |
| 1182 | .so tabs |
| 1183 | .DE |
| 1184 | Limits can be set, e.g.: |
| 1185 | .DS |
| 1186 | limit coredumpsize 128k |
| 1187 | .DE |
| 1188 | Most reasonable units abbreviations will work; see the |
| 1189 | .I csh |
| 1190 | manual page for more details. |
| 1191 | .PP |
| 1192 | The |
| 1193 | .I logout |
| 1194 | command can be used to terminate a login shell which has |
| 1195 | .I ignoreeof |
| 1196 | set. |
| 1197 | .PP |
| 1198 | The |
| 1199 | .I rehash |
| 1200 | command causes the shell to recompute a table of where commands are |
| 1201 | located. This is necessary if you add a command to a directory |
| 1202 | in the current shell's search path and wish the shell to find it, |
| 1203 | since otherwise the hashing algorithm may tell the shell that the |
| 1204 | command wasn't in that directory when the hash table was computed. |
| 1205 | .PP |
| 1206 | The |
| 1207 | .I repeat |
| 1208 | command can be used to repeat a command several times. |
| 1209 | Thus to make 5 copies of the file |
| 1210 | .I one |
| 1211 | in the file |
| 1212 | .I five |
| 1213 | you could do |
| 1214 | .DS |
| 1215 | repeat 5 cat one >> five |
| 1216 | .DE |
| 1217 | .PP |
| 1218 | The |
| 1219 | .I setenv |
| 1220 | command can be used |
| 1221 | to set variables in the environment. |
| 1222 | Thus |
| 1223 | .DS |
| 1224 | setenv TERM adm3a |
| 1225 | .DE |
| 1226 | will set the value of the environment variable \s-2TERM\s0 |
| 1227 | to |
| 1228 | `adm3a'. |
| 1229 | A user program |
| 1230 | .I printenv |
| 1231 | exists which will print out the environment. |
| 1232 | It might then show: |
| 1233 | .DS |
| 1234 | % printenv |
| 1235 | HOME=/usr/bill |
| 1236 | SHELL=/bin/csh |
| 1237 | PATH=:/usr/ucb:/bin:/usr/bin:/usr/local |
| 1238 | TERM=adm3a |
| 1239 | USER=bill |
| 1240 | % |
| 1241 | .DE |
| 1242 | .PP |
| 1243 | The |
| 1244 | .I source |
| 1245 | command can be used to force the current shell to read commands from |
| 1246 | a file. |
| 1247 | Thus |
| 1248 | .DS |
| 1249 | source .cshrc |
| 1250 | .DE |
| 1251 | can be used after editing in a change to the |
| 1252 | .I \&.cshrc |
| 1253 | file which you wish to take effect right away. |
| 1254 | .PP |
| 1255 | The |
| 1256 | .I time |
| 1257 | command can be used to cause a command to be timed no matter how much |
| 1258 | \s-2CPU\s0 time it takes. |
| 1259 | Thus |
| 1260 | .DS |
| 1261 | % time cp /etc/rc /usr/bill/rc |
| 1262 | 0.0u 0.1s 0:01 8% 2+1k 3+2io 1pf+0w |
| 1263 | % time wc /etc/rc /usr/bill/rc |
| 1264 | 52 178 1347 /etc/rc |
| 1265 | 52 178 1347 /usr/bill/rc |
| 1266 | 104 356 2694 total |
| 1267 | 0.1u 0.1s 0:00 13% 3+3k 5+3io 7pf+0w |
| 1268 | % |
| 1269 | .DE |
| 1270 | indicates that the |
| 1271 | .I cp |
| 1272 | command used a negligible amount of user time (u) |
| 1273 | and about 1/10th of a system time (s); the elapsed time was 1 second (0:01), |
| 1274 | there was an average memory usage of 2k bytes of program space and 1k |
| 1275 | bytes of data space over the cpu time involved (2+1k); the program |
| 1276 | did three disk reads and two disk writes (3+2io), and took one page fault |
| 1277 | and was not swapped (1pf+0w). |
| 1278 | The word count command |
| 1279 | .I wc |
| 1280 | on the other hand used 0.1 seconds of user time and 0.1 seconds of system |
| 1281 | time in less than a second of elapsed time. |
| 1282 | The percentage `13%' indicates that over the period when it was active |
| 1283 | the command `wc' used an average of 13 percent of the available \s-2CPU\s0 |
| 1284 | cycles of the machine. |
| 1285 | .PP |
| 1286 | The |
| 1287 | .I unalias |
| 1288 | and |
| 1289 | .I unset |
| 1290 | commands can be used |
| 1291 | to remove aliases and variable definitions from the shell, and |
| 1292 | .I unsetenv |
| 1293 | removes variables from the environment. |
| 1294 | .NH 2 |
| 1295 | What else? |
| 1296 | .PP |
| 1297 | This concludes the basic discussion of the shell for terminal users. |
| 1298 | There are more features of the shell to be discussed here, and all |
| 1299 | features of the shell are discussed in its manual pages. |
| 1300 | One useful feature which is discussed later is the |
| 1301 | .I foreach |
| 1302 | built-in command which can be used to run the same command |
| 1303 | sequence with a number of different arguments. |
| 1304 | .PP |
| 1305 | If you intend to use \s-2UNIX\s0 a lot you should look through |
| 1306 | the rest of this document and the csh manual pages (section1) to become familiar |
| 1307 | with the other facilities which are available to you. |
| 1308 | .bp |