Open System Services Shell and Utilities Reference Manual (G06.28+, H06.05+)

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User Commands (k - l) ksh(1)

You can augment the environment for any simple command or function by preﬁxing it with one

or more parameter assignments. A parameter assignment argument is a word of the form

identiﬁer=value.

Thus, the following two expressions are equivalent (as far as the execution of command is con-

cerned):

TERM=450 command argument ...

(export TERM; TERM=450; command argument ...)

Functions

The function reserved word is used to deﬁne shell functions. Shell functions are read in and

stored internally. Alias names are resolved when the function is read. Functions are executed

like commands with the arguments passed as positional parameters. (See Execution.)

Functions execute in the same process as the caller and share all

ﬁles and the present working

directory with the caller. Traps caught by the caller are reset to their default action inside the

function. A trap condition that is not caught or ignored by the function causes the function to ter-

minate and the condition to be passed on to the caller. A trap on EXIT set inside a function is

executed after the function completes in the environment of the caller. Ordinarily, variables are

shared between the calling program and the function. However, the special command typeset

used within a function deﬁnes local variables whose scope includes the current function and all

functions it calls.

The special command return is used to return from function calls. Errors within functions return

control to the caller.

Function identiﬁers can be listed with the -f or +f option of the typeset special command. The

text of functions is also listed with -f. Functions can be undeﬁned with the -f option of the unset

special command.

Ordinarily, functions are unset when the shell executes a shell script. The -xf option of the

typeset command allows a function to be exported to scripts that are executed without a separate

invocation of the shell. Functions that need to be deﬁned across separate invocations of the shell

should be speciﬁed in the ENV ﬁle with the -xf option of typeset.

Jobs

If the monitor option of the set command is turned on, an interactive shell associates a job with

each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them

small integer numbers. When a job is started asynchronously with &, the shell prints a line that

looks like:

[1] 1234

This line indicates that the job, which was started asynchronously, was job number 1 and had one

(top-level) process, whose process ID was 1234.

If you are running a job and want to do something else, you can enter the Suspend key sequence

(normally <Ctrl-z>), which sends a SIGTSTP signal to the current job. The shell then normally

indicates that the job has been stopped, and it prints another prompt. You can then manipulate

the state of this job, putting it in the background with the bg command, or run some other com-

mands and then eventually bring the job back into the foreground with the foreground command

fg. The job suspension takes effect immediately, and corresponds to the Interrupt key sequence

in that pending output and unread input are discarded. A special key sequence, <Ctrl-y>, does

not generate a SIGTSTP signal until a program attempts to read it. (See the read(2) reference

page for more information.) This key sequence can usefully be typed ahead when you have

prepared some commands for a job that you wish to stop after it has read them.

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