CODEWITHSUNDEEP
bashshell
Zenet
Zenet

Reputation: 7401

check if a line is empty using bash

I am trying to do a simple comparison to check if a line is empty using bash:

line=$(cat test.txt | grep mum )
if [ "$line" -eq "" ]
        then
        echo "mum is not there"
    fi

But it is not working, it says: [: too many arguments

Thanks a lot for your help!

Upvotes: 16

Views: 37389

Answers (7)

Thusitha Sumanadasa
Thusitha Sumanadasa

Reputation: 1761

If you want to use PHP with this,

$path_to_file='path/to/your/file';
$line = trim(shell_exec("grep 'mum' $path_to_file |wc -l"));
if($line==1){
   echo 'mum is not here';
}
else{
   echo 'mum is here';
}

Upvotes: -2

mllamazares
mllamazares

Reputation: 8166

I think the clearest solution is using regex:

if [[ "$line" =~ ^$ ]]; then
    echo "line empty"
else
    echo "line not empty"
fi

Upvotes: 2

Philipp
Philipp

Reputation: 49802

if line=$(grep -s -m 1 -e mum file.txt)
then
    echo "Found line $line"
else
    echo 'Nothing found or error occurred'
fi

Upvotes: 4

Anders
Anders

Reputation: 6218

if [ ${line:-null} = null ]; then
    echo "line is empty"
fi

or

if [ -z "${line}" ]; then
    echo "line is empty"
fi

Upvotes: 8

ghostdog74
ghostdog74

Reputation: 342283

grep "mum" file || echo "empty"

Upvotes: 4

schot
schot

Reputation: 11268

The classical sh answer that will also work in bash is

if [ x"$line" = x ]
then
    echo "empty"
fi

Your problem could also be that you are using '-eq' which is for arithmetic comparison.

Upvotes: 5

mjschultz
mjschultz

Reputation: 2026

You could also use the $? variable that is set to the return status of the command. So you'd have:

line=$(grep mum test.txt)
if [ $? -eq 1 ]
    then
    echo "mum is not there"
fi

For the grep command if there are any matches $? is set to 0 (exited cleanly) and if there are no matches $? is 1.

Upvotes: 27

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