BASH > Variable checking

BASH> Variable checking

Check the variable is a whole number

if [ $VARIABLE -eq $VARIABLE 2> /dev/null ]; then
echo $VARIABLE is a number
else
echo $VARIABLE is not a number
fi

Check the variable is not empty

if [ $VARIABLE != "" ] ; then
<code_to_execute>
else
echo "Error: VARIABLE is empty"
fi

or as provided by solstice:

if [ -z "$VARIABLE" ] ; then
echo “VARIABLE is empty”
else
echo “VARIABLE is not empty”
fi

or -n to test if it”s not null

if [ -n "$VARIABLE" ] ; then
echo “VARIABLE is not empty”
else
echo “VARIABLE is empty”
fi

Check the variable is alpha only

if [[ "$VARIABLE" =~ ^[a-zA-Z]+$ ]] ; then
echo "Variable contains letters only"
else
echo "Error"
fi

Posted in BASH

solstice

November 21, 2010 at 12:24 pm

to check for an empty variable, you can use -z
if [ -z “$VARIABLE” ] ; then
echo “$VARIABLE is empty”
else
echo “$VARIABLE is not empty”
fi

or -n to test if it”s not null
if [ -n “$VARIABLE” ] ; then
echo “$VARIABLE is not empty”
else
echo “$VARIABLE is empty”
fi

-n can be confusing so I stick with -z only.
scottro

November 22, 2010 at 8:07 pm

Thanks soltstice, I’ll add when I’m back at my desk 😉

BASH> Variable checking