diff options
Diffstat (limited to 'share/doc/usd/04.csh/csh.1')
| -rw-r--r-- | share/doc/usd/04.csh/csh.1 | 1009 |
1 files changed, 1009 insertions, 0 deletions
diff --git a/share/doc/usd/04.csh/csh.1 b/share/doc/usd/04.csh/csh.1 new file mode 100644 index 000000000000..5ae17b76650b --- /dev/null +++ b/share/doc/usd/04.csh/csh.1 @@ -0,0 +1,1009 @@ +.\"- +.\" 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. 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. +.\" +.EH 'USD:4-%''An Introduction to the C shell' +.OH 'An Introduction to the C shell''USD:4-%' +.\".RP +.TL +An Introduction to the C shell +.AU +William Joy +(revised for 4.3BSD by Mark Seiden) +.AI +Computer Science Division +.br +Department of Electrical Engineering and Computer Science +.br +University of California, Berkeley +.br +Berkeley, California 94720 +.AB +.I Csh +is a new command language interpreter for +.UX +systems. +It incorporates good features of other shells and a +.I history +mechanism similar to the +.I redo +of \s-2INTERLISP\s0. +While incorporating many features of other shells which make +writing shell programs (shell scripts) easier, +most of the features unique to +.I csh +are designed more for the interactive \s-2UNIX\s0 user. +.PP +\s-2UNIX\s0 +users who have read a general introduction to the system +will find a valuable basic explanation of the shell here. +Simple terminal interaction with +.I csh +is possible after reading just the first section of this document. +The second section describes the shell's capabilities which you can +explore after you have begun to become acquainted with the shell. +Later sections introduce features which are useful, but not necessary +for all users of the shell. +.PP +Additional information includes an appendix listing special characters of the shell +and a glossary of terms and commands introduced in this manual. +.AE +.SH +.if n .ND +Introduction +.PP +A +.I shell +is a command language interpreter. +.I Csh +is the name of one particular command interpreter on +\s-2UNIX\s0. +The primary purpose of +.I csh +is to translate command lines typed at a terminal into +system actions, such as invocation of other programs. +.I Csh +is a user program just like any you might write. +Hopefully, +.I csh +will be a very useful program for you +in interacting with the \s-2UNIX\s0 system. +.PP +In addition to this document, you will want to refer to a copy +of the \s-2UNIX\s0 User Reference Manual. +The +.I csh +documentation in section 1 of the manual provides a full description of all +features of the shell and is the definitive reference for questions +about the shell. +.PP +Many words in this document are shown in +.I italics. +These are important words; +names of commands, and words which have special meaning in discussing +the shell and \s-2UNIX\s0. +Many of the words are defined in a glossary at the end of this document. +If you don't know what is meant by a word, you should look +for it in the glossary. +.SH +Acknowledgements +.PP +Numerous people have provided good input about previous versions +of +.I csh +and aided in its debugging and in the debugging of its documentation. +I would especially like to thank Michael Ubell +who made the crucial observation that history commands could be +done well over the word structure of input text, and implemented +a prototype history mechanism in an older version of the shell. +Eric Allman has also provided a large number of useful comments on the +shell, helping to unify those concepts which are present and to identify +and eliminate useless and marginally useful features. +Mike O'Brien suggested the pathname hashing +mechanism which speeds command execution. +Jim Kulp added the job control and directory stack primitives and +added their documentation to this introduction. +.br +.bp +.NH +Terminal usage of the shell +.NH 2 +The basic notion of commands +.PP +A +.I shell +in +\s-2UNIX\s0 +acts mostly as a medium through which other +.I programs +are invoked. +While it has a set of +.I builtin +functions which it performs directly, +most commands cause execution of programs that are, in fact, +external to the shell. +The shell is thus distinguished from the command interpreters of other +systems both by the fact that it is just a user program, and by the fact +that it is used almost exclusively as a mechanism for invoking other programs. +.PP +.I Commands +in the \s-2UNIX\s0 system consist of a list of strings or +.I words +interpreted as a +.I "command name" +followed by +.I arguments. +Thus the command +.DS +mail bill +.DE +consists of two words. +The first word +.I mail +names the command to be executed, in this case the +mail program which sends messages to other users. +The shell uses the name of the command in attempting to execute it for you. +It will look in a number of +.I directories +for a file with the name +.I mail +which is expected to contain the mail program. +.PP +The rest of the words of the command are given as +.I arguments +to the command itself when it is executed. +In this case we specified also the argument +.I bill +which is interpreted by the +.I mail +program to be the name of a user to whom mail is to be sent. +In normal terminal usage we might use the +.I mail +command as follows. +.DS +% mail bill +I have a question about the csh documentation. +My document seems to be missing page 5. +Does a page five exist? + Bill +EOT +% +.DE +.PP +Here we typed a message to send to +.I bill +and ended this message with a ^D which sent an end-of-file to +the mail program. +(Here and throughout this document, the notation ``^\fIx\fR'' +is to be read ``control-\fIx\fR'' and represents the striking of the \fIx\fR +key while the control key is held down.) +The mail program +then echoed the characters `EOT' and transmitted our message. +The characters `% ' were printed before and after the mail command +by the shell to indicate that input was needed. +.PP +After typing the `% ' prompt the shell was reading command input from +our terminal. +We typed a complete command `mail bill'. +The shell then executed the +.I mail +program with argument +.I bill +and went dormant waiting for it to complete. +The mail program then read input from our terminal until we signalled +an end-of-file via typing a ^D after which the shell noticed +that mail had completed +and signaled us that it was ready to read from the terminal again by +printing another `% ' prompt. +.PP +This is the essential pattern of all interaction with \s-2UNIX\s0 +through the shell. +A complete command is typed at the terminal, the shell executes +the command and when this execution completes, it prompts for a new command. +If you run the editor for an hour, the shell will patiently wait for +you to finish editing and obediently prompt you again whenever you finish +editing. +.PP +An example of a useful command you can execute now is the +.I tset +command, which sets the default +.I erase +and +.I kill +characters on your terminal \- the erase character erases the last +character you typed and the kill character erases the entire line you +have entered so far. +By default, the erase character is the delete key (equivalent to `^?') +and the kill character is `^U'. Some people prefer to make the erase character +the backspace key (equivalent to `^H'). +You can make this be true by typing +.DS +tset \-e +.DE +which tells the program +.I tset +to set the erase character to tset's default setting for this character +(a backspace). +.NH 2 +Flag arguments +.PP +A useful notion in \s-2UNIX\s0 is that of a +.I flag +argument. +While many arguments to commands specify file names or user names, +some arguments rather specify an optional capability of the command +which you wish to invoke. +By convention, such arguments begin with the character `\-' (hyphen). +Thus the command +.DS +ls +.DE +will produce a list of the files in the current +.I "working directory" . +The option +.I \-s +is the size option, and +.DS +ls \-s +.DE +causes +.I ls +to also give, for each file the size of the file in blocks of 512 +characters. +The manual section for each command in the \s-2UNIX\s0 reference manual +gives the available options for each command. +The +.I ls +command has a large number of useful and interesting options. +Most other commands have either no options or only one or two options. +It is hard to remember options of commands which are not used very +frequently, so most \s-2UNIX\s0 utilities perform only one or two functions +rather than having a large number of hard to remember options. +.NH 2 +Output to files +.PP +Commands that normally read input or write output on the terminal +can also be executed with this input and/or output done to +a file. +.PP +Thus suppose we wish to save the current date in a file called `now'. +The command +.DS +date +.DE +will print the current date on our terminal. +This is because our terminal is the default +.I "standard output" +for the date command and the date command prints the date on its +standard output. +The shell lets us +.I redirect +the +.I "standard output" +of a command through a +notation using the +.I metacharacter +`>' and the name of the file where output is to be placed. +Thus the command +.DS +date > now +.DE +runs the +.I date +command such that its standard output is +the file `now' rather than the terminal. +Thus this command places the current date and time into the file `now'. +It is important to know that the +.I date +command was unaware that its output was going to a file rather than +to the terminal. +The shell performed this +.I redirection +before the command began executing. +.PP +One other thing to note here is that the file `now' +need not have existed before the +.I date +command was executed; the shell would have created the file if it did +not exist. +And if the file did exist? +If it had existed previously these previous contents would have been discarded! +A shell option +.I noclobber +exists to prevent this from happening accidentally; +it is discussed in section 2.2. +.PP +The system normally keeps files which you create with `>' and all other files. +Thus the default is for files to be permanent. If you wish to create a file +which will be removed automatically, you can begin its name with a `#' +character, this `scratch' character denotes the fact that the file will +be a scratch file.* +.FS +*Note that if your erase character is a `#', you will have to precede the +`#' with a `\e'. The fact that the `#' character is the old (pre-\s-2CRT\s0) +standard erase character means that it seldom appears in a file name, and +allows this convention to be used for scratch files. If you are using a +\s-2CRT\s0, your erase character should be a ^H, as we demonstrated +in section 1.1 how this could be set up. +.FE +The system will remove such files after a couple of days, +or sooner if file space becomes very tight. +Thus, in running the +.I date +command above, we don't really want to save the output forever, so we +would more likely do +.DS +date > #now +.DE +.NH 2 +Metacharacters in the shell +.PP +The shell has a large number of +special characters (like `>') +which indicate special functions. +We say that these notations have +.I syntactic +and +.I semantic +meaning to the shell. +In general, most characters which are neither letters nor digits +have special meaning to the shell. +We shall shortly learn a means of +.I quotation +which allows us to use +.I metacharacters +without the shell treating them in any special way. +.PP +Metacharacters normally have effect only when the shell is reading +our input. +We need not worry about placing shell metacharacters in a letter +we are sending via +.I mail, +or when we are typing in text or data to some other program. +Note that the shell is only reading input when it has prompted with +`% ' (although we can type our input even before it prompts). +.NH 2 +Input from files; pipelines +.PP +We learned above how to +.I redirect +the +.I "standard output" +of a command +to a file. +It is also possible to redirect the +.I "standard input" +of a command from a file. +This is not often necessary since most commands will read from +a file whose name is given as an argument. +We can give the command +.DS +sort < data +.DE +to run the +.I sort +command with standard input, where the command normally +reads its input, from the file +`data'. +We would more likely say +.DS +sort data +.DE +letting the +.I sort +command open the file +`data' +for input itself since this is less to type. +.PP +We should note that if we just typed +.DS +sort +.DE +then the sort program would sort lines from its +.I "standard input." +Since we did not +.I redirect +the standard input, it would sort lines as we typed them on the terminal +until we typed a ^D to indicate an end-of-file. +.PP +A most useful capability is the ability to combine the standard output +of one command with the standard input of another, i.e. to run the +commands in a sequence known as a +.I pipeline. +For instance the command +.DS +ls \-s +.DE +normally produces a list of the files in our directory with the size +of each in blocks of 512 characters. +If we are interested in learning which of our files is largest we +may wish to have this sorted by size rather than by name, which is +the default way in which +.I ls +sorts. +We could look at the many options of +.I ls +to see if there was an option to do this but would eventually discover +that there is not. +Instead we can use a couple of simple options of the +.I sort +command, combining it with +.I ls +to get what we want. +.PP +The +.I \-n +option of sort specifies a numeric sort rather than an alphabetic sort. +Thus +.DS +ls \-s | sort \-n +.DE +specifies that the output of the +.I ls +command run with the option +.I \-s +is to be +.I piped +to the command +.I sort +run with the numeric sort option. +This would give us a sorted list of our files by size, but with the +smallest first. +We could then use the +.I \-r +reverse sort option and the +.I head +command in combination with the previous command doing +.DS +ls \-s | sort \-n \-r | head \-5 +.DE +Here we have taken a list of our files sorted alphabetically, +each with the size in blocks. +We have run this to the standard input of the +.I sort +command asking it to sort numerically in reverse order (largest first). +This output has then been run into the command +.I head +which gives us the first few lines. +In this case we have asked +.I head +for the first 5 lines. +Thus this command gives us the names and sizes of our 5 largest files. +.PP +The notation introduced above is called the +.I pipe +mechanism. +Commands separated by `\||\|' characters are connected together by the +shell and the standard output of each is run into the standard input of the +next. +The leftmost command in a pipeline will normally take its standard +input from the terminal and the rightmost will place its standard +output on the terminal. +Other examples of pipelines will be given later when we discuss the +history mechanism; +one important use of pipes which is illustrated there is in the +routing of information to the line printer. +.NH 2 +Filenames +.PP +Many commands to be executed will need the names of files as arguments. +\s-2UNIX\s0 +.I pathnames +consist of a number of +.I components +separated by `/'. +Each component except the last names a directory in which the next +component resides, in effect specifying the +.I path +of directories to follow to reach the file. +Thus the pathname +.DS +/etc/motd +.DE +specifies a file in the directory +`etc' +which is a subdirectory of the +.I root +directory `/'. +Within this directory the file named is `motd' which stands +for `message of the day'. +A +.I pathname +that begins with a slash is said to be an +.I absolute +pathname since it is specified from the absolute top of the entire +directory hierarchy of the system (the +.I root ). +.I Pathnames +which do not begin with `/' are interpreted as starting in the current +.I "working directory" , +which is, by default, your +.I home +directory and can be changed dynamically by the +.I cd +change directory command. +Such pathnames are said to be +.I relative +to the working directory since they are found by starting +in the working directory and descending to lower levels of directories +for each +.I component +of the pathname. If the pathname contains no slashes at all then the +file is contained in the working directory itself and the pathname is merely +the name of the file in this directory. +Absolute pathnames have no relation +to the working directory. +.PP +Most filenames consist of a number of alphanumeric characters and +`.'s (periods). +In fact, all printing characters except `/' (slash) may appear in filenames. +It is inconvenient to have most non-alphabetic characters in filenames +because many of these have special meaning to the shell. +The character `.' (period) is not a shell-metacharacter and is often used +to separate the +.I extension +of a file name from the base of the name. +Thus +.DS +prog.c prog.o prog.errs prog.output +.DE +are four related files. +They share a +.I base +portion of a name +(a base portion being that part of the name that is left when a trailing +`.' and following characters which are not `.' are stripped off). +The file +`prog.c' +might be the source for a C program, +the file `prog.o' the corresponding object file, +the file +`prog.errs' the errors resulting from a compilation of the program +and the file +`prog.output' the output of a run of the program. +.PP +If we wished to refer to all four of these files in a command, we could +use the notation +.DS +prog.* +.DE +This expression is expanded by the shell, before the command to which it is +an argument is executed, into a list of names which begin with `prog.'. +The character `*' here matches any sequence (including the empty sequence) +of characters in a file name. +The names which match are alphabetically sorted and placed in the +.I "argument list" +of the command. +Thus the command +.DS +echo prog.* +.DE +will echo the names +.DS +prog.c prog.errs prog.o prog.output +.DE +Note that the names are in sorted order here, and a different +order than we listed them above. +The +.I echo +command receives four words as arguments, even though we only typed +one word as an argument directly. +The four words were generated by +.I "filename expansion" +of the one input word. +.PP +Other notations for +.I "filename expansion" +are also available. +The character `?' matches any single character in a filename. +Thus +.DS +echo ? \|?? \|??? +.DE +will echo a line of filenames; first those with one character names, +then those with two character names, and finally those with three +character names. +The names of each length will be independently sorted. +.PP +Another mechanism consists of a sequence of characters between `[' and `]'. +This metasequence matches any single character from the enclosed set. +Thus +.DS +prog.[co] +.DE +will match +.DS +prog.c prog.o +.DE +in the example above. +We can also place two characters around a `\-' in this notation to denote +a range. +Thus +.DS +chap.[1\-5] +.DE +might match files +.DS +chap.1 chap.2 chap.3 chap.4 chap.5 +.DE +if they existed. +This is shorthand for +.DS +chap.[12345] +.DE +and otherwise equivalent. +.PP +An important point to note is that if a list of argument words to +a command (an +.I "argument list)" +contains filename expansion syntax, and if this filename expansion syntax +fails to match any existing file names, then the shell considers this +to be an error and prints a diagnostic +.DS +No match. +.DE +and does not execute the command. +.PP +Another very important point is that files with the character `.' at the +beginning are treated specially. +Neither `*' or `?' or the `[' `]' mechanism will match it. +This prevents accidental matching of the filenames `.' and `..' +in the working directory which have special meaning to the system, +as well as other files such as +.I \&.cshrc +which are not normally +visible. +We will discuss the special role of the file +.I \&.cshrc +later. +.PP +Another filename expansion mechanism gives access to the pathname of +the +.I home +directory of other users. +This notation consists of the character `~' (tilde) followed by another user's +login name. +For instance the word `~bill' would map to the pathname `/usr/bill' +if the home directory for `bill' was `/usr/bill'. +Since, on large systems, users may have login directories scattered over +many different disk volumes with different prefix directory names, +this notation provides a convenient way of accessing the files +of other users. +.PP +A special case of this notation consists of a `~' alone, e.g. `~/mbox'. +This notation is expanded by the shell into the file `mbox' in your +.I home +directory, i.e. into `/usr/bill/mbox' for me on Ernie Co-vax, the UCB +Computer Science Department VAX machine, where this document was prepared. +This can be very useful if you have used +.I cd +to change to another directory and have found a file you wish to +copy using +.I cp. +If I give the command +.DS +cp thatfile ~ +.DE +the shell will expand this command to +.DS +cp thatfile /usr/bill +.DE +since my home directory is /usr/bill. +.PP +There also exists a mechanism using the characters `{' and `}' for +abbreviating a set of words which have common parts but cannot +be abbreviated by the above mechanisms because they are not files, +are the names of files which do not yet exist, +are not thus conveniently described. +This mechanism will be described much later, +in section 4.2, +as it is used less frequently. +.NH 2 +Quotation +.PP +We have already seen a number of metacharacters used by the shell. +These metacharacters pose a problem in that we cannot use them directly +as parts of words. +Thus the command +.DS +echo * +.DE +will not echo the character `*'. +It will either echo a sorted list of filenames in the +current +.I "working directory," +or print the message `No match' if there are +no files in the working directory. +.PP +The recommended mechanism for placing characters which are neither numbers, +digits, `/', `.' or `\-' in an argument word to a command is to enclose +it with single quotation characters `\'', i.e. +.DS +echo \'*\' +.DE +There is one special character `!' which is used by the +.I history +mechanism of the shell and which cannot be +.I escaped +by placing it within `\'' characters. +It and the character `\'' itself can be preceded by a single `\e' +to prevent their special meaning. +Thus +.DS +echo \e\'\e! +.DE +prints +.DS +\'! +.DE +These two mechanisms suffice to place any printing character into a word +which is an argument to a shell command. They can be combined, as in +.DS +echo \e\'\'*\' +.DE +which prints +.DS +\'* +.DE +since the first `\e' escaped the first `\'' and the `*' was enclosed +between `\'' characters. +.NH 2 +Terminating commands +.PP +When you are executing a command and the shell is +waiting for it to complete there are several ways +to force it to stop. +For instance if you type the command +.DS +cat /etc/passwd +.DE +the system will print a copy of a list of all users of the system +on your terminal. +This is likely to continue for several minutes unless you stop it. +You can send an +\s-2INTERRUPT\s0 +.I signal +to the +.I cat +command by typing ^C on your terminal.* +.FS +*On some older Unix systems the \s-2DEL\s0 or \s-2RUBOUT\s0 key +has the same effect. "stty all" will tell you the INTR key value. +.FE +Since +.I cat +does not take any precautions to avoid or otherwise handle this signal +the +\s-2INTERRUPT\s0 +will cause it to terminate. +The shell notices that +.I cat +has terminated and prompts you again with `% '. +If you hit \s-2INTERRUPT\s0 again, the shell will just +repeat its prompt since it handles \s-2INTERRUPT\s0 signals +and chooses to continue to execute commands rather than terminating +like +.I cat +did, which would have the effect of logging you out. +.PP +Another way in which many programs terminate is when they get an end-of-file +from their standard input. +Thus the +.I mail +program in the first example above was terminated when we typed a ^D +which generates an end-of-file from the standard input. +The shell also terminates when it gets an end-of-file printing `logout'; +\s-2UNIX\s0 then logs you off the system. +Since this means that typing too many ^D's can accidentally log us off, +the shell has a mechanism for preventing this. +This +.I ignoreeof +option will be discussed in section 2.2. +.PP +If a command has its standard input redirected from a file, then it will +normally terminate when it reaches the end of this file. +Thus if we execute +.DS +mail bill < prepared.text +.DE +the mail command will terminate without our typing a ^D. +This is because it read to the end-of-file of our file +`prepared.text' in which we placed a message for `bill' with an editor program. +We could also have done +.DS +cat prepared.text \||\| mail bill +.DE +since the +.I cat +command would then have written the text through the pipe to the +standard input of the mail command. +When the +.I cat +command completed it would have terminated, +closing down the pipeline +and the +.I mail +command would have received an end-of-file from it and terminated. +Using a pipe here is more complicated than redirecting input +so we would more likely use the first form. +These commands could also have been stopped by sending an \s-2INTERRUPT\s0. +.PP +Another possibility for stopping a command is to suspend its execution +temporarily, with the possibility of continuing execution later. This is +done by sending a \s-2STOP\s0 signal via typing a ^Z. +This signal causes all commands running on the terminal +(usually one but more if a pipeline is executing) to become suspended. +The shell notices that the command(s) have been suspended, types +`Stopped' and then prompts for a new command. +The previously executing command has been suspended, but otherwise +unaffected by the \s-2STOP\s0 signal. Any other commands can be executed +while the original command remains suspended. The suspended command can +be continued using the +.I fg +command with no arguments. The shell will then retype the command +to remind you which command is being continued, and cause the command +to resume execution. Unless any input files in use by the suspended +command have been changed in the meantime, the suspension has no effect +whatsoever on the execution of the command. This feature can be very useful +during editing, when you need to look at another file before continuing. +An +example of command suspension follows. +.DS +% mail harold +Someone just copied a big file into my directory and its name is +^Z +Stopped +% ls +funnyfile +prog.c +prog.o +% jobs +.ta 1.75i +[1] + Stopped mail harold +% fg +mail harold +funnyfile. Do you know who did it? +EOT +% +.so tabs +.DE +In this example someone was sending a message to Harold and forgot the +name of the file he wanted to mention. The mail command was suspended +by typing ^Z. When the shell noticed that the mail program was +suspended, it typed `Stopped' and prompted for a new command. Then the +.I ls +command was typed to find out the name of the file. The +.I jobs +command was run to find out which command was suspended. +At this time the +.I fg +command was typed to continue execution of the mail program. Input +to the mail program was then continued and ended with a ^D +which indicated the end of the message at which time the mail +program typed EOT. The +.I jobs +command will show which commands are suspended. +The ^Z should only be typed at the beginning of a line since +everything typed on the current line is discarded when a signal is sent +from the keyboard. This also happens on \s-2INTERRUPT\s0, and \s-2QUIT\s0 +signals. More information on +suspending jobs and controlling them is given in +section 2.6. +.PP +If you write or run programs which are not fully debugged then it may +be necessary to stop them somewhat ungracefully. +This can be done by sending them a \s-2QUIT\s0 +signal, sent by typing a ^\e. +This will usually provoke the shell to produce a message like: +.DS +Quit (Core dumped) +.DE +indicating that a file +`core' has been created containing information about the running program's +state when it terminated due to the \s-2QUIT\s0 signal. +You can examine this file yourself, or forward information to the +maintainer of the program telling him/her where the +.I "core file" +is. +.PP +If you run background commands (as explained in section 2.6) then these +commands will ignore \s-2INTERRUPT\s0 and \s-2QUIT\s0 signals at the +terminal. To stop them you must use the +.I kill +command. See section 2.6 for an example. +.PP +If you want to examine the output of a command without having it move +off the screen as the output of the +.DS +cat /etc/passwd +.DE +command will, you can use the command +.DS +more /etc/passwd +.DE +The +.I more +program pauses after each complete screenful and types `\-\-More\-\-' +at which point you can hit a space to get another screenful, a return +to get another line, a `?' to get some help on other commands, or a `q' to end the +.I more +program. You can also use more as a filter, i.e. +.DS +cat /etc/passwd | more +.DE +works just like the more simple more command above. +.PP +For stopping output of commands not involving +.I more +you can use the +^S key to stop the typeout. The typeout will resume when you +hit ^Q or any other key, but ^Q is normally used because +it only restarts the output and does not become input to the program +which is running. This works well on low-speed terminals, but at 9600 +baud it is hard to type ^S and ^Q fast enough to paginate +the output nicely, and a program like +.I more +is usually used. +.PP +An additional possibility is to use the ^O flush output +character; when this character is typed, all output from the current +command is thrown away (quickly) until the next input read occurs +or until the next shell prompt. This can be used to allow a command +to complete without having to suffer through the output on a slow +terminal; ^O is a toggle, so flushing can be turned off by +typing ^O again while output is being flushed. +.NH 2 +What now? +.PP +We have so far seen a number of mechanisms of the shell and learned a lot +about the way in which it operates. +The remaining sections will go yet further into the internals of the +shell, but you will surely want to try using the +shell before you go any further. +To try it you can log in to \s-2UNIX\s0 and type the following +command to the system: +.DS +chsh myname /bin/csh +.DE +Here `myname' should be replaced by the name you typed to +the system prompt of `login:' to get onto the system. +Thus I would use `chsh bill /bin/csh'. +.B +You only have to do this once; it takes effect at next login. +.R +You are now ready to try using +.I csh. +.PP +Before you do the `chsh' command, the shell you are using when +you log into the system is `/bin/sh'. +In fact, much of the above discussion is applicable to `/bin/sh'. +The next section will introduce many features particular to +.I csh +so you should change your shell to +.I csh +before you begin reading it. +.bp |