topic bash and sh difference in break this while do loop in Operating System - Linux

bash and sh difference in break this while do loop

jamesps — Fri, 10 Feb 2006 13:47:37 GMT

This is an extract from /opt/VRTS/bin/vxrootmir

tfound=no
tmpdg=
mdm=
mda=

vxdisk -q list | \
while read da type dm grp state rest
do
if [ "$dm" = "$1" ]; then
tmpdg=$grp
mdm=$1
tfound=yes
break
elif [ "$da" = "$1" ]; then
if [ "$dm" != "-" ]; then
tmpdg=$grp
mdm=$dm
fi
tfound=yes
break
fi
done

if [ "$tfound" = "no" ]; then
abort "Disk $1 not found in configuration" vxvmshm:0
fi

Here's what I would like to explain: under bash (3.00.14) the tfound variable is set to "no" again after it is set to "yes" and breaks after the first if. Because of that the disk not found message is displayed and the script exits unsuccessfully.

This behavior does not happen under sh. It looks so simple but... why?

Thanks!
james

Re: bash and sh difference in break this while do loop

jamesps — Fri, 10 Feb 2006 13:52:12 GMT

I am using B.11.11, latest security patches.

Re: bash and sh difference in break this while do loop

James R. Ferguson — Fri, 10 Feb 2006 14:00:39 GMT

Hi James:

I'd use 'set -x' and perhaps add 'set -v' and trace the execution and variable setting.

Regards!

...JRF...

Re: bash and sh difference in break this while do loop

A. Clay Stephenson — Fri, 10 Feb 2006 15:00:35 GMT

I suspect that your read is the problem.

Try this very simple test:

echo "One Two Three" | read A B C
echo "A = \"${A}\""
echo "B = \"${B}\""
echo "C = \"${C}\""

I think you will find different results in the POSIX shell and bash -- at least some implementations of bash. It's one of the reasons I'm not a huge fan of bash. My shell of choice under Linix is zsh.

Re: bash and sh difference in break this while do loop

Kent Ostby — Fri, 10 Feb 2006 15:10:43 GMT

Perhaps it should be == instead of = in

if [ "$tfound" = "no" ]; then