Nighthawk: Pushed from thelinuxwiki.com.

2013-02-25T19:01:57Z

Pushed from thelinuxwiki.com.

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The -n operator checks whether the string is not null. Effectively, this will return true for every case except where the string contains no characters. ie:

VAR="hello"
if [ -n "$VAR" ]; then
echo "VAR is not empty"
fi

Similarly, the -z operator checks whether the string is null. ie:

VAR=""
if [ -z "$VAR" ]; then
echo "VAR is empty"
fi

Note the spaces around the square brackets. Bash will complain if the spaces are not there.

'''example using null check to see if a drive is mounted'''
volume="toshibaHD"
check=$(mount|grep $volume)
if [ -n "$check" ]
then
echo "\$check is NOT null"
else
echo "\$check IS null"
fi

[[category:bash]]

Bash null check - Revision history

Nighthawk: Pushed from thelinuxwiki.com.