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

sh
current ERR and EXIT traps, as well as any flags manipulated by EXIT with
the set command; these are restored when the function finishes. The
function ends either by falling off the end of the code of the function body,
or by reaching a return statement. If the function uses typeset to declare
any variables in the function body, the variables are local to the function.
if command then command [elif command then command] ... [else command] fi
In the if statement, if the first (leftmost) command succeeds (returns a zero
exit status), sh runs the command following then. Otherwise, sh runs the
command (if any) following the elif (which is short for “else if”); if that
succeeds, sh runs the command following the next then. If neither case
succeeds, sh runs the command following the else (if any).
select variable [in word ...] do commands done
The select statement can handle menulike interactions with the user. Its
syntax is like the for statement. Each word is printed on the standard error
file, one per line, with an accompanying number. If you omit the “in word ...”
part, sh uses the positional parameters. sh then displays the value of the
variable PS3 to prompt the user to enter a numerical reply. If the reply is an
empty line, sh displays the menu again; otherwise, sh assigns the input line
to the variable REPLY, sets variable to the word selected, and then runs
the commands. sh does this over and over until the loop is ended by an
interrupt, an end-of-file, or an explicit break statement in the commands.
until command1 do command2 done
The until statement runs command1 and tests its exit status for success
(zero) or failure (nonzero). If command1 succeeds, the loop ends;
otherwise, sh runs command2 and then goes back to run and test
command1 again. break and continue commands in the commands can
affect the operation of the loop.
while command1 do command2 done
The while statement works similarly to the until statement. However, the
loop ends whenever command1 is unsuccessful (nonzero exit status).
Shell reserved words are recognized only when they are the unquoted first token of
a command. This lets you pass these reserved words as arguments to commands
run from the shell. The full list of reserved words is:
! done function while
[[ elif if
{ else select
} esac then
case fi time
do for until
Command Execution
Before running a simple command,the shell processes the command line,
performing expansion, assignments, and redirection.
First, sh examines the command line and divides it into a series of tokens, which
are either operators or words. An operator is either a control operator, which is
described in “Command Syntax” on page 551. Or it can be a redirection operator,
described in “File Descriptors and Redirection” on page 564. A word is any token
that is not an operator.
Next, the shell expands words in the following order:
1. sh performs directory substitution.
556 z/OS V1R9.0 UNIX System Services Command Reference