scope of variable in pipe

Question

The following shell scrip will check the disk space and change the variable diskfull to 1 if the usage is more than 10% The last echo always shows

Answer 1

When using pipes the shell seams to use sub-shells to do the work. As $diskfull is not known to these sub-shells the value is never changed.

See: http://www.nucleardonkey.net/blog/2007/08/variable_scope_in_bash.html

I modified your script as follows. It works for me and should work on your system too.

#!/bin/sh
diskfull=0

ALERT=10
stats=`df -HP | grep -vE '^Filesystem|tmpfs|cdrom|none|udev' | awk '{ print $5 "_" $1 }'`
for output in $stats
do
  usep=$(echo $output | awk '{ print $1}' | cut -d'%' -f1  )
  partition=$(echo $output | sed s/.*_// )
  #echo $partition -  $usep
  if [ $usep -le $ALERT ]; then
     diskfull=1
     break
  fi
done
echo $diskfull