Most people think the Bourne shell's while loop ( 44.10 ) looks like this, with a single command controlling the loop:
whilecommand
do ...whatever done
But
command
can actually be a
list
of commands. The exit status of the last command controls the loop. This is handy for prompting users and reading answers - when the user types an empty answer, the
read
command returns "false" and the loop ends:
while echo "Enter command or CTRL-d to quit: \c" read command do ...process$command
done
Here's a loop that runs
who
and does a quick search on its output. If the
grep
returns non-zero status (because it doesn't find
$who
in
$tempfile
), the loop quits - otherwise, the loop does lots of processing:
while who > $tempfile grep "$who" $tempfile >/dev/null do ...process $tempfile... done
-