How to check if file is empty or it has only blank characters?

This will notify us if the file is empty:

[[ ! -s $file ]] && echo "hello there I am empty file !!!"

But how to check if a file has blank spaces (spaces or tabs)?

• empty file can include empty spaces / TAB

Answers:

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Method 1

Just grep for a character other than space:

grep -q '[^[:space:]]' < "$file" &&
  printf '%sn' "$file contains something else than whitespace characters"

Method 2

Similar to the other answers but using a negated grep -q

if ! grep -q '[^[:space:]]' "$file"; then
    echo "file is empty"
else
    echo "File has data"
fi

Method 3

If you want to check for empty file content within an if condition [[ ... ]], then surround the grep with -z $( grep ... ) (without -q):

if [[ -z $(grep '[^[:space:]]' $file) ]] ; then
  echo "Empty file" 
  ...
fi

I had to use this, in order to avoid following error when running:

$ [[ grep -q '[^[:space:]]' $file ]]

-bash: conditional binary operator expected

-bash: syntax error near `-q’

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0