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diff --git a/bin/csh/USD.doc/csh.2 b/bin/csh/USD.doc/csh.2 new file mode 100644 index 000000000000..610105c829fa --- /dev/null +++ b/bin/csh/USD.doc/csh.2 @@ -0,0 +1,1305 @@ +.\" Copyright (c) 1980, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" This product includes software developed by the University of +.\" California, Berkeley and its contributors. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" @(#)csh.2 8.1 (Berkeley) 6/8/93 +.\" +.nr H1 1 +.NH +Details on the shell for terminal users +.NH 2 +Shell startup and termination +.PP +When you login, the shell is started by the system in your +.I home +directory and begins by reading commands from a file +.I \&.cshrc +in this directory. +All shells which you may start during your terminal session will +read from this file. +We will later see what kinds of commands are usefully placed there. +For now we need not have this file and the shell does not complain about +its absence. +.PP +A +.I "login shell" , +executed after you login to the system, +will, after it reads commands from +.I \&.cshrc, +read commands from a file +.I \&.login +also in your home directory. +This file contains commands which you wish to do each time you login +to the \s-2UNIX\s0 system. +My +.I \&.login +file looks something like: +.DS +set ignoreeof +set mail=(/usr/spool/mail/bill) +echo "${prompt}users" ; users +alias ts \e + \'set noglob ; eval \`tset \-s \-m dialup:c100rv4pna \-m plugboard:?hp2621nl \!*\`\'; +ts; stty intr ^C kill ^U crt +set time=15 history=10 +msgs \-f +if (\-e $mail) then + echo "${prompt}mail" + mail +endif +.DE +.PP +This file contains several commands to be executed by \s-2UNIX\s0 +each time I login. +The first is a +.I set +command which is interpreted directly by the shell. It sets the shell +variable +.I ignoreeof +which causes the shell to not log me off if I hit ^D. Rather, +I use the +.I logout +command to log off of the system. +By setting the +.I mail +variable, I ask the shell to watch for incoming mail to me. Every 5 minutes +the shell looks for this file and tells me if more mail has arrived there. +An alternative to this is to put the command +.DS +biff y +.DE +in place of this +.I set; +this will cause me to be notified immediately when mail arrives, and to +be shown the first few lines of the new message. +.PP +Next I set the shell variable `time' to `15' causing the shell to automatically +print out statistics lines for commands which execute for at least 15 seconds +of \s-2CPU\s+2 time. The variable `history' is set to 10 indicating that +I want the shell to remember the last 10 commands I type in its +.I "history list" , +(described later). +.PP +I create an +.I alias +``ts'' which executes a +\fItset\fR\|(1) command setting up the modes of the terminal. +The parameters to +.I tset +indicate the kinds of terminal which I usually use when not on a hardwired +port. I then execute ``ts'' and also use the +.I stty +command to change the interrupt character to ^C and the line kill +character to ^U. +.PP +I then run the `msgs' program, which provides me with any +system messages which I have not seen before; the `\-f' option here prevents +it from telling me anything if there are no new messages. +Finally, if my mailbox file exists, then I run the `mail' program to +process my mail. +.PP +When the `mail' and `msgs' programs finish, the shell will finish +processing my +.I \&.login +file and begin reading commands from the terminal, prompting for each with +`% '. +When I log off (by giving the +.I logout +command) the shell +will print `logout' and execute commands from the file `.logout' +if it exists in my home directory. +After that the shell will terminate and \s-2UNIX\s0 will log +me off the system. +If the system is not going down, I will receive a new login message. +In any case, after the `logout' message the shell is committed to terminating +and will take no further input from my terminal. +.NH 2 +Shell variables +.PP +The shell maintains a set of +.I variables. +We saw above the variables +.I history +and +.I time +which had values `10' and `15'. +In fact, each shell variable has as value an array of +zero or more +.I strings. +Shell variables may be assigned values by the set command. It has +several forms, the most useful of which was given above and is +.DS +set name=value +.DE +.PP +Shell variables may be used to store values which are to +be used in commands later through a substitution mechanism. +The shell variables most commonly referenced are, however, those which the +shell itself refers to. +By changing the values of these variables one can directly affect the +behavior of the shell. +.PP +One of the most important variables is the variable +.I path. +This variable contains a sequence of directory names where the shell +searches for commands. +The +.I set +command with no arguments +shows the value of all variables currently defined (we usually say +.I set) +in the shell. +The default value for path will be shown by +.I set +to be +.DS +% set +.ta .75i +argv () +cwd /usr/bill +home /usr/bill +path (. /usr/ucb /bin /usr/bin) +prompt % +shell /bin/csh +status 0 +term c100rv4pna +user bill +% +.so tabs +.DE +This output indicates that the variable path points to the current +directory `.' and then `/usr/ucb', `/bin' and `/usr/bin'. +Commands which you may write might be in `.' (usually one of +your directories). +Commands developed at Berkeley, live in `/usr/ucb' +while commands developed at Bell Laboratories live in `/bin' and `/usr/bin'. +.PP +A number of locally developed programs on the system live in the directory +`/usr/local'. +If we wish that all shells which we invoke to have +access to these new programs we can place the command +.DS +set path=(. /usr/ucb /bin /usr/bin /usr/local) +.DE +in our file +.I \&.cshrc +in our home directory. +Try doing this and then logging out and back in and do +.DS +set +.DE +again to see that the value assigned to +.I path +has changed. +.FS \(dg +Another directory that might interest you is /usr/new, which contains +many useful user-contributed programs provided with Berkeley Unix. +.FE +.PP +One thing you should be aware of is that the shell examines each directory +which you insert into your path and determines which commands are contained +there. Except for the current directory `.', which the shell treats specially, +this means that if commands are added to a directory in your search path after +you have started the shell, they will not necessarily be found by the shell. +If you wish to use a command which has been added in this way, you should +give the command +.DS +rehash +.DE +to the shell, which will cause it to recompute its internal table of command +locations, so that it will find the newly added command. +Since the shell has to look in the current directory `.' on each command, +placing it at the end of the path specification usually works equivalently +and reduces overhead. +.PP +Other useful built in variables are the variable +.I home +which shows your home directory, +.I cwd +which contains your current working directory, +the variable +.I ignoreeof +which can be set in your +.I \&.login +file to tell the shell not to exit when it receives an end-of-file from +a terminal (as described above). +The variable `ignoreeof' +is one of several variables which the shell does not care about the +value of, only whether they are +.I set +or +.I unset. +Thus to set this variable you simply do +.DS +set ignoreeof +.DE +and to unset it do +.DS +unset ignoreeof +.DE +These give the variable `ignoreeof' no value, but none is desired or required. +.PP +Finally, some other built-in shell variables of use are the +variables +.I noclobber +and +.I mail. +The metasyntax +.DS +> filename +.DE +which redirects the standard output of a command +will overwrite and destroy the previous contents of the named file. +In this way you may accidentally overwrite a file which is valuable. +If you would prefer that the shell not overwrite files in this +way you can +.DS +set noclobber +.DE +in your +.I \&.login +file. +Then trying to do +.DS +date > now +.DE +would cause a diagnostic if `now' existed already. +You could type +.DS +date >! now +.DE +if you really wanted to overwrite the contents of `now'. +The `>!' is a special metasyntax indicating that clobbering the +file is ok.\(dg +.FS +\(dgThe space between the `!' and the word `now' is critical here, as `!now' +would be an invocation of the +.I history +mechanism, and have a totally different effect. +.FE +.NH 2 +The shell's history list +.PP +The shell can maintain a +.I "history list" +into which it places the words +of previous commands. +It is possible to use a notation to reuse commands or words +from commands in forming new commands. +This mechanism can be used to repeat previous commands or to +correct minor typing mistakes in commands. +.PP +The following figure gives a sample session involving typical usage of the +history mechanism of the shell. +.KF +.DS +% cat bug.c +main() + +{ + printf("hello); +} +% cc !$ +cc bug.c +"bug.c", line 4: newline in string or char constant +"bug.c", line 5: syntax error +% ed !$ +ed bug.c +29 +4s/);/"&/p + printf("hello"); +w +30 +q +% !c +cc bug.c +% a.out +hello% !e +ed bug.c +30 +4s/lo/lo\e\en/p + printf("hello\en"); +w +32 +q +% !c \-o bug +cc bug.c \-o bug +% size a.out bug +a.out: 2784+364+1028 = 4176b = 0x1050b +bug: 2784+364+1028 = 4176b = 0x1050b +% ls \-l !* +ls \-l a.out bug +\(mirwxr\(mixr\(mix 1 bill 3932 Dec 19 09:41 a.out +\(mirwxr\(mixr\(mix 1 bill 3932 Dec 19 09:42 bug +% bug +hello +% num bug.c | spp +spp: Command not found. +% ^spp^ssp +num bug.c | ssp + 1 main() + 3 { + 4 printf("hello\en"); + 5 } +% !! | lpr +num bug.c | ssp | lpr +% +.DE +.KE +In this example we have a very simple C program which has a bug (or two) +in it in the file `bug.c', which we `cat' out on our terminal. We then +try to run the C compiler on it, referring to the file again as `!$', +meaning the last argument to the previous command. Here the `!' is the +history mechanism invocation metacharacter, and the `$' stands for the last +argument, by analogy to `$' in the editor which stands for the end of the line. +The shell echoed the command, as it would have been typed without use of +the history mechanism, and then executed it. +The compilation yielded error diagnostics so we now run the editor on the +file we were trying to compile, fix the bug, and run the C compiler again, +this time referring to this command simply as `!c', which repeats the last +command which started with the letter `c'. If there were other +commands starting with `c' done recently we could have said `!cc' or even +`!cc:p' which would have printed the last command starting with `cc' +without executing it. +.PP +After this recompilation, we ran the resulting `a.out' file, and then +noting that there still was a bug, ran the editor again. After fixing +the program we ran the C compiler again, but tacked onto the command +an extra `\-o bug' telling the compiler to place the resultant binary in +the file `bug' rather than `a.out'. In general, the history mechanisms +may be used anywhere in the formation of new commands and other characters +may be placed before and after the substituted commands. +.PP +We then ran the `size' command to see how large the binary program images +we have created were, and then an `ls \-l' command with the same argument +list, denoting the argument list `\!*'. +Finally we ran the program `bug' to see that its output is indeed correct. +.PP +To make a numbered listing of the program we ran the `num' command on the file `bug.c'. +In order to compress out blank lines in the output of `num' we ran the +output through the filter `ssp', but misspelled it as spp. To correct this +we used a shell substitute, placing the old text and new text between `^' +characters. This is similar to the substitute command in the editor. +Finally, we repeated the same command with `!!', but sent its output to the +line printer. +.PP +There are other mechanisms available for repeating commands. The +.I history +command prints out a number of previous commands with numbers by which +they can be referenced. There is a way to refer to a previous command +by searching for a string which appeared in it, and there are other, +less useful, ways to select arguments to include in a new command. +A complete description of all these mechanisms +is given in the C shell manual pages in the \s-2UNIX\s0 Programmer's Manual. +.NH 2 +Aliases +.PP +The shell has an +.I alias +mechanism which can be used to make transformations on input commands. +This mechanism can be used to simplify the commands you type, +to supply default arguments to commands, +or to perform transformations on commands and their arguments. +The alias facility is similar to a macro facility. +Some of the features obtained by aliasing can be obtained also +using shell command files, but these take place in another instance +of the shell and cannot directly affect the current shells environment +or involve commands such as +.I cd +which must be done in the current shell. +.PP +As an example, suppose that there is a new version of the mail program +on the system called `newmail' +you wish to use, rather than the standard mail program which is called +`mail'. +If you place the shell command +.DS +alias mail newmail +.DE +in your +.I \&.cshrc +file, the shell will transform an input line of the form +.DS +mail bill +.DE +into a call on `newmail'. +More generally, suppose we wish the command `ls' to always show +sizes of files, that is to always do `\-s'. +We can do +.DS +alias ls ls \-s +.DE +or even +.DS +alias dir ls \-s +.DE +creating a new command syntax `dir' +which does an `ls \-s'. +If we say +.DS +dir ~bill +.DE +then the shell will translate this to +.DS +ls \-s /mnt/bill +.DE +.PP +Thus the +.I alias +mechanism can be used to provide short names for commands, +to provide default arguments, +and to define new short commands in terms of other commands. +It is also possible to define aliases which contain multiple +commands or pipelines, showing where the arguments to the original +command are to be substituted using the facilities of the +history mechanism. +Thus the definition +.DS +alias cd \'cd \e!* ; ls \' +.DE +would do an +.I ls +command after each change directory +.I cd +command. +We enclosed the entire alias definition in `\'' characters to prevent +most substitutions from occurring and the character `;' from being +recognized as a metacharacter. +The `!' here is escaped with a `\e' to prevent it from being interpreted +when the alias command is typed in. +The `\e!*' here substitutes the entire argument list to the pre-aliasing +.I cd +command, without giving an error if there were no arguments. +The `;' separating commands is used here +to indicate that one command is to be done and then the next. +Similarly the definition +.DS +alias whois \'grep \e!^ /etc/passwd\' +.DE +defines a command which looks up its first argument in the password file. +.PP +.B Warning: +The shell currently reads the +.I \&.cshrc +file each time it starts up. If you place a large number of commands +there, shells will tend to start slowly. A mechanism for saving the shell +environment after reading the \fI\&.cshrc\fR file and quickly restoring it is +under development, but for now you should try to limit the number of +aliases you have to a reasonable number... 10 or 15 is reasonable, +50 or 60 will cause a noticeable delay in starting up shells, and make +the system seem sluggish when you execute commands from within the editor +and other programs. +.NH 2 +More redirection; >> and >& +.PP +There are a few more notations useful to the terminal user +which have not been introduced yet. +.PP +In addition to the standard output, commands also have a +.I "diagnostic output" +which is normally directed to the terminal even when the standard output +is redirected to a file or a pipe. +It is occasionally desirable to direct the diagnostic output along with +the standard output. +For instance if you want to redirect the output of a long running command +into a file and wish to have a record of any error diagnostic it produces +you can do +.DS +command >& file +.DE +The `>&' here tells the shell to route both the diagnostic output and the +standard output into `file'. +Similarly you can give the command +.DS +command |\|& lpr +.DE +to route both standard and diagnostic output through the pipe +to the line printer daemon +.I lpr.\(dd +.FS +\(dd A command of the form +.br +.ti +5 +command >&! file +.br +exists, and is used when +.I noclobber +is set and +.I file +already exists. +.FE +.PP +Finally, it is possible to use the form +.DS +command >> file +.DE +to place output at the end of an existing file.\(dg +.FS +\(dg If +.I noclobber +is set, then an error will result if +.I file +does not exist, otherwise the shell will create +.I file +if it doesn't exist. +A form +.br +.ti +5 +command >>! file +.br +makes it not be an error for file to not exist when +.I noclobber +is set. +.FE +.NH 2 +Jobs; Background, Foreground, or Suspended +.PP +When one or more commands +are typed together as a pipeline or as a sequence of commands separated by +semicolons, a single +.I job +is created by the shell consisting of these commands together as a unit. +Single commands without pipes or semicolons create the simplest jobs. +Usually, every line typed to the shell creates a job. +Some lines that create jobs (one per line) are +.DS +sort < data +ls \-s | sort \-n | head \-5 +mail harold +.DE +.PP +If the metacharacter `&' is typed +at the end of the commands, then the job is started as a +.I background +job. This means that the shell does not wait for it to complete but +immediately prompts and is ready for another command. The job runs +.I "in the background" +at the same time that normal jobs, called +.I foreground +jobs, continue to be read and executed by the shell one at a time. +Thus +.DS +du > usage & +.DE +would run the +.I du +program, which reports on the disk usage of your working directory (as well as +any directories below it), put the output into the file `usage' and return +immediately with a prompt for the next command without out waiting for +.I du +to finish. The +.I du +program would continue executing in the background +until it finished, even though you can type and execute more commands in the +mean time. +When a background +job terminates, a message is typed by the shell just before the next prompt +telling you that the job has completed. +In the following example the +.I du +job finishes sometime during the +execution of the +.I mail +command and its completion is reported just before +the prompt after the +.I mail +job is finished. +.DS +% du > usage & +[1] 503 +% mail bill +How do you know when a background job is finished? +EOT +.ta 1.75i +[1] \- Done du > usage +% +.so tabs +.DE +If the job did not terminate normally the `Done' message might say +something else like `Killed'. +If you want the +terminations of background jobs to be reported at the time they occur +(possibly interrupting the output of other foreground jobs), you can set +the +.I notify +variable. In the previous example this would mean that the +`Done' message might have come right in the middle of the message to +Bill. +Background jobs are unaffected by any signals from the keyboard like +the \s-2STOP\s0, \s-2INTERRUPT\s0, or \s-2QUIT\s0 signals mentioned earlier. +.PP +Jobs are recorded in a table inside the shell until they terminate. +In this table, the shell remembers the command names, arguments and the +.I "process numbers" +of all commands in the job as well as the working directory where the job was +started. +Each job in the table is either running +.I "in the foreground" +with the shell waiting for it to terminate, running +.I "in the background," +or +.I suspended. +Only one job can be running in the foreground at one time, but several +jobs can be suspended or running in the background at once. As each job +is started, it is assigned a small identifying +number called the +.I "job number" +which can be used later to refer to the job in the commands described below. +Job numbers remain +the same until the job terminates and then are re-used. +.PP +When a job is started in the backgound using `&', its number, as well +as the process numbers of all its (top level) commands, is typed by the shell +before prompting you for another command. For example, +.DS +% ls \-s | sort \-n > usage & +[2] 2034 2035 +% +.DE +runs the `ls' program with the `\-s' options, pipes this output into +the `sort' program with the `\-n' option which puts its output into the +file `usage'. +Since the `&' was at the end of the line, these two programs were started +together as a background job. After starting the job, the shell prints +the job number in brackets (2 in this case) followed by the process number +of each program started in the job. Then the shell immediates prompts for +a new command, leaving the job running simultaneously. +.PP +As mentioned in section 1.8, foreground jobs become +.I suspended +by typing ^Z +which sends a \s-2STOP\s0 signal to the currently running +foreground job. A background job can become suspended by using the +.I stop +command described below. When jobs are suspended they merely stop +any further progress until started again, either in the foreground +or the backgound. The shell notices when a job becomes stopped and +reports this fact, much like it reports the termination of background jobs. +For foreground jobs this looks like +.DS +% du > usage +^Z +Stopped +% +.DE +`Stopped' message is typed by the shell when it notices that the +.I du +program stopped. +For background jobs, using the +.I stop +command, it is +.DS +% sort usage & +[1] 2345 +% stop %1 +.ta 1.75i +[1] + Stopped (signal) sort usage +% +.so tabs +.DE +Suspending foreground jobs can be very useful when you need to temporarily +change what you are doing (execute other commands) and then return to +the suspended job. Also, foreground jobs can be suspended and then +continued as background jobs using the +.I bg +command, allowing you to continue other work and +stop waiting for the foreground job to finish. Thus +.DS +% du > usage +^Z +Stopped +% bg +[1] du > usage & +% +.DE +starts `du' in the foreground, stops it before it finishes, then continues +it in the background allowing more foreground commands to be executed. +This is especially helpful +when a foreground job ends up taking longer than you expected and you +wish you had started it in the backgound in the beginning. +.PP +All +.I "job control" +commands can take an argument that identifies a particular +job. +All job name arguments begin with the character `%', since some of the +job control commands also accept process numbers (printed by the +.I ps +command.) +The default job (when no argument is given) is called the +.I current +job and is identified by a `+' in the output of the +.I jobs +command, which shows you which jobs you have. +When only one job is stopped or running in the background (the usual case) +it is always the current job thus no argument is needed. +If a job is stopped while running in the foreground it becomes the +.I current +job and the existing current job becomes the +.I previous +job \- identified by a `\-' in the output of +.I jobs. +When the current job terminates, the previous job becomes the current job. +When given, the argument is either `%\-' (indicating +the previous job); `%#', where # is the job number; +`%pref' where pref is some unique prefix of the command name +and arguments of one of the jobs; or `%?' followed by some string found +in only one of the jobs. +.PP +The +.I jobs +command types the table of jobs, giving the job number, +commands and status (`Stopped' or `Running') of each backgound or +suspended job. With the `\-l' option the process numbers are also +typed. +.DS +% du > usage & +[1] 3398 +% ls \-s | sort \-n > myfile & +[2] 3405 +% mail bill +^Z +Stopped +% jobs +.ta 1.75i +[1] \(mi Running du > usage +[2] Running ls \-s | sort \-n > myfile +[3] \(pl Stopped mail bill +% fg %ls +ls \-s | sort \-n > myfile +% more myfile +.so tabs +.DE +.PP +The +.I fg +command runs a suspended or background job in the foreground. It is +used to restart a previously suspended job or change a background job +to run in the foreground (allowing signals or input from the terminal). +In the above example we used +.I fg +to change the `ls' job from the +background to the foreground since we wanted to wait for it to +finish before looking at its output file. +The +.I bg +command runs a suspended job in the background. It is usually used +after stopping the currently running foreground job with the +\s-2STOP\s0 signal. The combination of the \s-2STOP\s0 signal and the +.I bg +command changes a foreground job into a background job. +The +.I stop +command suspends a background job. +.PP +The +.I kill +command terminates a background or suspended job immediately. +In addition to jobs, it may be given process numbers as arguments, +as printed by +.I ps. +Thus, in the example above, the running +.I du +command could have been terminated by the command +.DS +% kill %1 +.ta 1.75i +[1] Terminated du > usage +% +.so tabs +.DE +.PP +The +.I notify +command (not the variable mentioned earlier) indicates that the termination +of a specific job should be +reported at the time it finishes instead of waiting for the next prompt. +.PP +If a job running in the background tries to read input from the terminal +it is automatically stopped. When such a job is then run in the +foreground, input can be given to the job. If desired, the job can +be run in the background again until it requests input again. +This is illustrated in the following sequence where the `s' command in the +text editor might take a long time. +.ID +.nf +% ed bigfile +120000 +1,$s/thisword/thatword/ +^Z +Stopped +% bg +[1] ed bigfile & +% + . . . some foreground commands +.ta 1.75i +[1] Stopped (tty input) ed bigfile +% fg +ed bigfile +w +120000 +q +% +.so tabs +.DE +So after the `s' command was issued, the `ed' job was stopped with ^Z +and then put in the background using +.I bg. +Some time later when the `s' command was finished, +.I ed +tried to read another command and was stopped because jobs +in the backgound cannot read from the terminal. The +.I fg +command returned the `ed' job to the foreground where it could once again +accept commands from the terminal. +.PP +The command +.DS +stty tostop +.DE +causes all background jobs run on your terminal to stop +when they are about to +write output to the terminal. This prevents messages from background +jobs from interrupting foreground job output and allows you to run +a job in the background without losing terminal output. It also +can be used for interactive programs that sometimes have long +periods without interaction. Thus each time it outputs a prompt for more +input it will stop before the prompt. It can then be run in the +foreground using +.I fg, +more input can be given and, if necessary stopped and returned to +the background. This +.I stty +command might be a good thing to put in your +.I \&.login +file if you do not like output from background jobs interrupting +your work. It also can reduce the need for redirecting the output +of background jobs if the output is not very big: +.DS +% stty tostop +% wc hugefile & +[1] 10387 +% ed text +\&. . . some time later +q +.ta 1.75i +[1] Stopped (tty output) wc hugefile +% fg wc +wc hugefile + 13371 30123 302577 +% stty \-tostop +.so tabs +.DE +Thus after some time the `wc' command, which counts the lines, words +and characters in a file, had one line of output. When it tried to +write this to the terminal it stopped. By restarting it in the +foreground we allowed it to write on the terminal exactly when we were +ready to look at its output. +Programs which attempt to change the mode of the terminal will also +block, whether or not +.I tostop +is set, when they are not in the foreground, as +it would be very unpleasant to have a background job change the state +of the terminal. +.PP +Since the +.I jobs +command only prints jobs started in the currently executing shell, +it knows nothing about background jobs started in other login sessions +or within shell files. The +.I ps +can be used in this case to find out about background jobs not started +in the current shell. +.NH 2 +Working Directories +.PP +As mentioned in section 1.6, the shell is always in a particular +.I "working directory." +The `change directory' command +.I chdir +(its +short form +.I cd +may also be used) +changes the working directory of the shell, +that is, changes the directory you +are located in. +.PP +It is useful to make a directory for each project you wish to work on +and to place all files related to that project in that directory. +The `make directory' command, +.I mkdir, +creates a new directory. +The +.I pwd +(`print working directory') command +reports the absolute pathname of the working directory of the shell, +that is, the directory you are +located in. +Thus in the example below: +.DS +% pwd +/usr/bill +% mkdir newpaper +% chdir newpaper +% pwd +/usr/bill/newpaper +% +.DE +the user has created and moved to the +directory +.I newpaper. +where, for example, he might +place a group of related files. +.PP +No matter where you have moved to in a directory hierarchy, +you can return to your `home' login directory by doing just +.DS +cd +.DE +with no arguments. +The name `..' always means the directory above the current one in +the hierarchy, thus +.DS +cd .. +.DE +changes the shell's working directory to the one directly above the +current one. +The name `..' can be used in any +pathname, thus, +.DS +cd ../programs +.DE +means +change to the directory `programs' contained in the directory +above the current one. +If you have several directories for different +projects under, say, your home directory, +this shorthand notation +permits you to switch easily between them. +.PP +The shell always remembers the pathname of its current working directory in +the variable +.I cwd. +The shell can also be requested to remember the previous directory when +you change to a new working directory. If the `push directory' command +.I pushd +is used in place of the +.I cd +command, the shell saves the name of the current working directory +on a +.I "directory stack" +before changing to the new one. +You can see this list at any time by typing the `directories' +command +.I dirs. +.ID +.nf +% pushd newpaper/references +~/newpaper/references ~ +% pushd /usr/lib/tmac +/usr/lib/tmac ~/newpaper/references ~ +% dirs +/usr/lib/tmac ~/newpaper/references ~ +% popd +~/newpaper/references ~ +% popd +~ +% +.DE +The list is printed in a horizontal line, reading left to right, +with a tilde (~) as +shorthand for your home directory\(emin this case `/usr/bill'. +The directory stack is printed whenever there is more than one +entry on it and it changes. +It is also printed by a +.I dirs +command. +.I Dirs +is usually faster and more informative than +.I pwd +since it shows the current working directory as well as any +other directories remembered in the stack. +.PP +The +.I pushd +command with no argument +alternates the current directory with the first directory in the +list. +The `pop directory' +.I popd +command without an argument returns you to the directory you were in prior to +the current one, discarding the previous current directory from the +stack (forgetting it). +Typing +.I popd +several times in a series takes you backward through the directories +you had been in (changed to) by +.I pushd +command. +There are other options to +.I pushd +and +.I popd +to manipulate the contents of the directory stack and to change +to directories not at the top of the stack; see the +.I csh +manual page for details. +.PP +Since the shell remembers the working directory in which each job +was started, it warns you when you might be confused by restarting +a job in the foreground which has a different working directory than the +current working directory of the shell. Thus if you start a background +job, then change the shell's working directory and then cause the +background job to run in the foreground, the shell warns you that the +working directory of the currently running foreground job is different +from that of the shell. +.DS +% dirs \-l +/mnt/bill +% cd myproject +% dirs +~/myproject +% ed prog.c +1143 +^Z +Stopped +% cd .. +% ls +myproject +textfile +% fg +ed prog.c (wd: ~/myproject) +.DE +This way the shell warns you when there +is an implied change of working directory, even though no cd command was +issued. In the above example the `ed' job was still in `/mnt/bill/project' +even though the shell had changed to `/mnt/bill'. +A similar warning is given when such a foreground job +terminates or is suspended (using the \s-2STOP\s0 signal) since +the return to the shell again implies a change of working directory. +.DS +% fg +ed prog.c (wd: ~/myproject) + . . . after some editing +q +(wd now: ~) +% +.DE +These messages are sometimes confusing if you use programs that change +their own working directories, since the shell only remembers which +directory a job is started in, and assumes it stays there. +The `\-l' option of +.I jobs +will type the working directory +of suspended or background jobs when it is different +from the current working directory of the shell. +.NH 2 +Useful built-in commands +.PP +We now give a few of the useful built-in commands of the shell describing +how they are used. +.PP +The +.I alias +command described above is used to assign new aliases and to show the +existing aliases. +With no arguments it prints the current aliases. +It may also be given only one argument such as +.DS +alias ls +.DE +to show the current alias for, e.g., `ls'. +.PP +The +.I echo +command prints its arguments. +It is often used in +.I "shell scripts" +or as an interactive command +to see what filename expansions will produce. +.PP +The +.I history +command will show the contents of the history list. +The numbers given with the history events can be used to reference +previous events which are difficult to reference using the +contextual mechanisms introduced above. +There is also a shell variable called +.I prompt. +By placing a `!' character in its value the shell will there substitute +the number of the current command in the history list. +You can use this number to refer to this command in a history substitution. +Thus you could +.DS +set prompt=\'\e! % \' +.DE +Note that the `!' character had to be +.I escaped +here even within `\'' characters. +.PP +The +.I limit +command is used to restrict use of resources. +With no arguments it prints the current limitations: +.DS +.ta 1i +cputime unlimited +filesize unlimited +datasize 5616 kbytes +stacksize 512 kbytes +coredumpsize unlimited +.so tabs +.DE +Limits can be set, e.g.: +.DS +limit coredumpsize 128k +.DE +Most reasonable units abbreviations will work; see the +.I csh +manual page for more details. +.PP +The +.I logout +command can be used to terminate a login shell which has +.I ignoreeof +set. +.PP +The +.I rehash +command causes the shell to recompute a table of where commands are +located. This is necessary if you add a command to a directory +in the current shell's search path and wish the shell to find it, +since otherwise the hashing algorithm may tell the shell that the +command wasn't in that directory when the hash table was computed. +.PP +The +.I repeat +command can be used to repeat a command several times. +Thus to make 5 copies of the file +.I one +in the file +.I five +you could do +.DS +repeat 5 cat one >> five +.DE +.PP +The +.I setenv +command can be used +to set variables in the environment. +Thus +.DS +setenv TERM adm3a +.DE +will set the value of the environment variable \s-2TERM\s0 +to +`adm3a'. +A user program +.I printenv +exists which will print out the environment. +It might then show: +.DS +% printenv +HOME=/usr/bill +SHELL=/bin/csh +PATH=:/usr/ucb:/bin:/usr/bin:/usr/local +TERM=adm3a +USER=bill +% +.DE +.PP +The +.I source +command can be used to force the current shell to read commands from +a file. +Thus +.DS +source .cshrc +.DE +can be used after editing in a change to the +.I \&.cshrc +file which you wish to take effect right away. +.PP +The +.I time +command can be used to cause a command to be timed no matter how much +\s-2CPU\s0 time it takes. +Thus +.DS +% time cp /etc/rc /usr/bill/rc +0.0u 0.1s 0:01 8% 2+1k 3+2io 1pf+0w +% time wc /etc/rc /usr/bill/rc + 52 178 1347 /etc/rc + 52 178 1347 /usr/bill/rc + 104 356 2694 total +0.1u 0.1s 0:00 13% 3+3k 5+3io 7pf+0w +% +.DE +indicates that the +.I cp +command used a negligible amount of user time (u) +and about 1/10th of a system time (s); the elapsed time was 1 second (0:01), +there was an average memory usage of 2k bytes of program space and 1k +bytes of data space over the cpu time involved (2+1k); the program +did three disk reads and two disk writes (3+2io), and took one page fault +and was not swapped (1pf+0w). +The word count command +.I wc +on the other hand used 0.1 seconds of user time and 0.1 seconds of system +time in less than a second of elapsed time. +The percentage `13%' indicates that over the period when it was active +the command `wc' used an average of 13 percent of the available \s-2CPU\s0 +cycles of the machine. +.PP +The +.I unalias +and +.I unset +commands can be used +to remove aliases and variable definitions from the shell, and +.I unsetenv +removes variables from the environment. +.NH 2 +What else? +.PP +This concludes the basic discussion of the shell for terminal users. +There are more features of the shell to be discussed here, and all +features of the shell are discussed in its manual pages. +One useful feature which is discussed later is the +.I foreach +built-in command which can be used to run the same command +sequence with a number of different arguments. +.PP +If you intend to use \s-2UNIX\s0 a lot you you should look through +the rest of this document and the csh manual pages (section1) to become familiar +with the other facilities which are available to you. +.bp |