APLawrence.com - Resources for Unix and Linux Systems, Bloggers and the self-employed

Why does this variable become blank?

Some material is very old and may be incorrect today

© July 2015 Anthony Lawrence

Anonymous asks:

Why does this variable become blank? It's obviously set in the first part, but it goes away.

who am i | if grep tony > /dev/null  2>&1
 then
 echo "Setting source directory to /usr1/src"
 export src_path=/usr1/src
 echo $src_path
 else
 src_path=/usr2/src
fi
echo -e "src_path= $src_path"

What happens here is actually very simple, although it may seem baffling at first. Yes, the "if then" block sets the variable to either /usr1/src or /usr2/src, so it surprised you to find it blank in the last line which echoed "src_path= $src_path".

What you missed is that piping "who am i" to that "if" block caused the creation of a new shell for everything in the block. Variables changed in a new shell don't change the values in the calling shell, so $src_path was still blank.

Something like this will work much better:

IAM=`who am i | cut -d" " -f1`

if [ $IAM == "tony" ]
 then
 ..

brinan White noted that the script will work in ksh

If you found something useful today, please consider a small donation.