Advanced Bash−Scripting Guide

As is the case with for/in loops, placing the do on the same line as the condition test requires a
semicolon.
while [condition] ; do
Advanced Bash−Scripting Guide
Note that certain specialized while loops, as, for example, a getopts construct, deviate somewhat from
the standard template given here.
Example 10−14. Simple while loop
#!/bin/bash
var0=0
LIMIT=10
while [ "$var0" −lt "$LIMIT" ]
do
echo −n "$var0 " # −n suppresses newline.
var0=`expr $var0 + 1` # var0=$(($var0+1)) also works.
done
echo
exit 0
Example 10−15. Another while loop
#!/bin/bash
echo
while [ "$var1" != "end" ] # while test "$var1" != "end"
do
# also works.
echo "Input variable #1 (end to exit) "
read var1
# Not 'read $var1' (why?).
echo "variable #1 = $var1" # Need quotes because of "#".
# If input is 'end', echoes it here.
# Does not test for termination condition until top of loop.
echo
done
exit 0
A while loop may have multiple conditions. Only the final condition determines when the loop
terminates. This necessitates a slightly different loop syntax, however.
Example 10−16. while loop with multiple conditions
#!/bin/bash
var1=unset
previous=$var1
while echo "previous−variable = $previous"
Chapter 10. Loops and Branches 111