How can I test if line is empty in shell script?

Question

I have a shell script like this:

cat file | while read line
do
    # run some commands using $line    
done

Now I need to check if the line contains any non-whitespace character ([\n\t ]), and if not, skip it. How can I do this?

Answer 1

Since read reads whitespace-delimited fields by default, a line containing only whitespace should result in the empty string being assigned to the variable, so you should be able to skip empty lines with just:

[ -z "$line" ] && continue

Answer 2

try this

while read line;
do 

    if [ "$line" != "" ]; then
        # Do something here
    fi

done < $SOURCE_FILE

Answer 3

bash:

if [[ ! $line =~ [^[:space:]] ]] ; then
  continue
fi

And use done < file instead of cat file | while, unless you know why you'd use the latter.