z/OS V1R9.0 UNIX System Services Command ... - Christian Grothoff

sh
Variables are named parameters.For details on naming and declaring variables, see
“Variables” on page 567.
The simplest way to use a parameter in a command line is to enter a dollar sign ($)
followed by the name of the parameter. For example, if you enter the command:
echo $x
sh replaces $x with the value of the parameter x and then displays the results
(because echo displays its arguments). Other ways to expand parameters are
shown in the following paragraphs.
The following parameters are built in to the shell:
$1, $2, ... $9
Expands to the d positional parameter (where d is the single digit following
the $). If there is no such parameter, $d expands to a null string.
$0 Expands to the name of the shell, the shell script, or a value assigned when
you invoked the shell.
$# Expands to the number of positional parameters.
$@ Expands to the complete list of positional parameters. If $@ is quoted, the
result is separate arguments, each quoted. This means that:
"$@"
is equivalent to:
"$1" "$2" ...
$* Expands to the complete list of positional parameters. If $* is quoted, the
result is concatenated into a single argument, with parameters separated by
the first character of the value of IFS (see “Variables” on page 567). For
example, if the first character of IFS is a blank, then:
"$*"
is equivalent to:
"$1 $2 ..."
$– Expands to all options that are in effect from previous calls to the set
command and from options on the sh command line.
$? Expands to the exit status of the last command run.
$$ Expands to the process ID of the shell. If running in a child shell
environment (see “Shell Execution Environments” on page 567), it is the
process ID of the parent shell. Otherwise, it is the process ID of the current
shell.
$! Expands to the process number of the last asynchronous command.
These constructs are called parameters of the shell. They include the positional
parameters, but are not restricted to the positional parameters.
We have already mentioned that you can expand a parameter by putting a $ in front
of the parameter name. More sophisticated ways to expand parameters are:
${parameter}
Expands any parameter.
${number}
Expands to the positional parameter with the given number. (Remember
560 z/OS V1R9.0 UNIX System Services Command Reference