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@(#)newcsh.1 4.1 (Berkeley) 04/29/85
"Jobs."
The most important new feature in this shell is the control of jobs. A job is associated with each pipeline, where a pipeline is either a simple command like ``date'', or a pipeline like ``who | wc''. The shell keeps a table of current jobs, and assigns them small integer numbers. When you start a job in the background, the shell prints a line which looks like:
[1] 1234
this indicating that the job which was started asynchronously with ``&'' is job number 1 and has one (top-level) process, whose process id is 1234. The set of current jobs is listed by the jobs command.
If you are running a job and wish to do something else you may hit the key ^Z (control-Z) which sends a stop signal to the current job. The shell will then normally indicate that the job has been ``Stopped'', and print another prompt. You can then put the job in the background with the command ``bg'', or run some other commands and then return the job to the foreground with ``fg''. A ^Z takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed. There is another special key ^Y which does not generate a stop signal until a program attempts to read (2) it. This can usefully be typed ahead when you have prepared some commands for a job which you wish to stop after it has read them.
A job being run in the background will stop if it tries to read from the terminal. Background jobs are normally allowed to produce output, but this can be disabled by doing ``stty tostop''. If you set this tty option, then background jobs will stop when they try to produce output like they do when they try to read input.
There are several ways to refer to jobs in the shell. The character ``%'' introduces a job name. If you wish to refer to job number 1, you can name it as ``%1''. Just naming a job brings it to the foreground; thus ``%1'' is a synonym for ``fg %1'', bringing job 1 back into the foreground. Similarly saying ``%1 &'' resumes job 1 in the background. Jobs can also be named by prefixes of the string typed in to start them, if these prefixes are unambiguous, thus ``%ex'' would normally restart a suspended ex (1) job, if there were only one suspended job whose name began with the string ``ex''. It is also possible to say ``%?string'' which specifies a job whose text contains string, if there is only one such job.
The shell also maintains a notion of the current and previous jobs. In output pertaining to jobs, the current job is marked with a ``+'' and the previous job with a ``-''. The abbreviation ``%+'' refers to the current job and ``%-'' refers to the previous job. For close analogy with the history mechanism, ``%%'' is also a synonym for the current job.
"Status reporting."
This shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work. If, however, you set the shell variable notify, the shell will notify you immediately of changes of status in background jobs. There is also a shell command notify which marks a single process so that its status changes will be immediately reported. By default notify marks the current process; simply say ``notify'' after starting a background job to mark it.
When you try to leave the shell while jobs are stopped, you will be warned that ``You have stopped jobs.'' You may use the ``jobs'' command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a second time, and the suspended jobs will be unmercifully terminated.
"New builtin commands."
5 bg
.ns
5 bg %job ...
Puts the current or specified jobs into the background, continuing them if they were stopped.
5 fg
.ns
5 fg %job ...
Brings the current or specified jobs into the foreground, continuing them if they were stopped.
5 jobs
.ns
5 "jobs -l"
Lists the active jobs; given the -l options lists process id's in addition to the normal information.
5 kill %job
.ns
5 kill -sig %job ...
.ns
5 kill pid
.ns
5 kill -sig pid ...
.ns
5 kill -l
Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in /usr/include/signal.h, stripped of the prefix ``SIG''). The signal names are listed by ``kill -l''. There is no default, saying just `kill' does not send a signal to the current job. If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process will be sent a CONT (continue) signal as well.
5 notify
.ns
5 notify %job ...
Causes the shell to notify the user asynchronously when the status of the current or specified jobs changes; normally notification is presented before a prompt. All jobs are marked ``notify'' if the shell variable ``notify'' is set.
5 stop %job ...
Stops the specified job which is executing in the background.
5 %job
Brings the specified job into the foreground.
5 %job &
Continues the specified job in the background.
"Process limitations."
The shell provides access to an experimental facility for limiting the consumption by a single process of system resources. The following commands control this facility:
5 limit resource maximum-use
5 limit resource
.ns
limit
Limits the consumption by the current process and each process it creates to not individually exceed maximum-use on the specified resource. If no maximum-use is given, then the current limit is printed; if no resource is given, then all limitations are given.
Resources controllable currently include cputime (the maximum number of cpu-seconds to be used by each process), filesize (the largest single file which can be created), datasize (the maximum growth of the data+stack region via sbrk (2) beyond the end of the program text), stacksize (the maximum size of the automatically-extended stack region), and coredumpsize (the size of the largest core dump that will be created). The maximum-use may be given as a (floating point or integer) number followed by a scale factor. For all limits other than cputime the default scale is ``k'' or ``kilobytes'' (1024 bytes); a scale factor of ``m'' or ``megabytes'' may also be used. For cputime the default scaling is ``seconds'', while ``m'' for minutes or ``h'' for hours, or a time of the form ``mm:ss'' giving minutes and seconds may be used. For both resource names and scale factors, unambiguous prefixes of the names suffice.5 unlimit resource
.ns
5 unlimit
Removes the limitation on resource. If no resource is specified, then all resource limitations are removed.
"Directory stack."
This shell now keeps track of the current directory (which is kept in the variable cwd) and also maintains a stack of directories, which is printed by the command dirs. You can change to a new directory and push down the old directory stack by using the command pushd which is otherwise like the chdir command, changing to its argument. You can pop the directory stack by saying popd. Saying pushd with no arguments exchanges the top two elements of the directory stack. The elements of the directory stack are numbered from 1 starting at the top. Saying pushd with a argument ``+n'' rotates the directory stack to make that entry in the stack be at the top and changes to it. Giving popd a ``+n'' argument eliminates that argument from the directory stack.
"Miscellaneous."
This shell imports the environment variable USER into the variable user, TERM into term, and HOME into home, and exports these back into the environment whenever the normal shell variables are reset. The environment variable PATH is likewise handled; it is not necessary to worry about its setting other than in the file .cshrc as inferior csh processes will import the definition of path from the environment, and re-export it if you then change it. (It could be set once in the .login except that commands over the Berknet would not see the definition.)
There are new commands eval, which is like the eval of the Bourne shell sh (1), and useful with tset (1), and suspend which stops a shell (as though a ^Z had stopped it; since shells normally ignore ^Z signals, this command is necessary.)
There is a new variable cdpath; if set, then each directory in cdpath will be searched for a directory named in a chdir command if there is no such subdirectory of the current directory.
An unsetenv command removing environment variables has been added.
There is a new ``:'' modifier ``:e'', which yields the extension portion of a filename. Thus if ``$a'' is ``file.c'', ``$a:e'' is ``c''.
There are two new operators in shell expressions ``!~'' and ``=~'' which are like the string operations ``!='' and ``=='' except that the right hand side is a pattern (containing, e.g. ``*''s, ``?''s and instances of ``[...]'') against which the left hand operand is matched. This reduces the need for use of the switch statement in shell scripts when all that is really needed is pattern matching.
The form ``$<'' is new, and is replaced by a line from the standard input, with no further interpretation thereafter. It may therefore be used to read from the keyboard in a shell script.
Shell builtin functions are not stoppable/restartable.
Control over output is primitive; perhaps this will inspire someone to work on a good virtual terminal interface. In a virtual terminal interface much more interesting things could be done with output control.