How to check if a file is empty in Bash?

[ -s file.name ] || echo "file is empty"

[ -s file ] # Checks if file has size greater than 0

[ -s diff.txt ] && echo "file has something" || echo "file is empty"

If needed, this checks all the *.txt files in the current directory; and reports all the empty file:

for file in *.txt; do if [ ! -s $file ]; then echo $file; fi; done

To check if file is empty or has only white spaces, you can use grep:

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

Easiest way for checking if file is empty or not:

if [ -s /path-to-file/filename.txt ]
then
     echo "File is not empty"
else
     echo "File is empty"
fi

You can also write it on single line:

[ -s /path-to-file/filename.txt ] && echo "File is not empty" || echo "File is empty"

While the other answers are correct, using the "-s" option will also show the file is empty even if the file does not exist.
By adding this additional check "-f" to see if the file exists first, we ensure the result is correct.

if [ -f diff.txt ]
then
  if [ -s diff.txt ]
  then
    rm -f empty.txt
    touch full.txt
  else
    rm -f full.txt
    touch empty.txt
  fi
else
  echo "File diff.txt does not exist"
fi

@geedoubleya answer is my favorite.

However, I do prefer this

if [[ -f diff.txt && -s diff.txt ]]
then
  rm -f empty.txt
  touch full.txt
elif [[ -f diff.txt && ! -s diff.txt ]]
then
  rm -f full.txt
  touch empty.txt
else
  echo "File diff.txt does not exist"
fi

[[ -f filename && ! -s filename ]] && echo "filename exists and is empty"

Many of the answers are correct but I feel like they could be more complete / simplistic etc. for example :

Example 1 : Basic if statement

# BASH4+ example on Linux :

typeset read_file="/tmp/some-file.txt"
if [ ! -s "${read_file}" ]  || [ ! -f "${read_file}" ] ;then
    echo "Error: file (${read_file}) not found.. "
    exit 7
fi

if $read_file is empty or not there stop the show with exit. More than once I have had misread the top answer here to mean the opposite.

Example 2 : As a function

# -- Check if file is missing /or empty --
# Globals: None
# Arguments: file name
# Returns: Bool
# --
is_file_empty_or_missing() {
    [[ ! -f "${1}" || ! -s "${1}" ]] && return 0 || return 1
}

Similar to @noam-manos's grep-based answer, I solved this using cat. For me, -s wasn't working because my "empty" file had >0 bytes.

if [[ ! -z $(cat diff.txt) ]] ; then
    echo "diff.txt is not empty"
else
    echo "diff.txt is empty"
fi

I came here looking for how to delete empty __init__.py files as they are implicit in Python 3.3+ and ended up using:

find -depth '(' -type f  -name __init__.py ')' -print0 |
  while IFS= read -d '' -r file; do if [[ ! -s $file ]]; then rm $file; fi; done

Also (at least in zsh) using $path as the variable also breaks your $PATH env and so it'll break your open shell. Anyway, thought I'd share!

1. (For the guys above) I'm not sure if you really want to use logical operators inside the [[ program. Probably you should use [[ expr_1 ]] && [[ expr_2 ]] instead of [[ expr_1 && expr_2 ]].
2. The expression [[ -s file.txt ]] also checks if the file exists, so I don't see any reason to use -f before that.

This a simple statement to check if a file exists, is not empty and contains 0:

if [[ ! -s ./example.txt  ]] || grep -q 0 "./example.txt"; then
  echo "example.txt doesn't exist, is empty or contains 0"
else
  echo "example.txt contains 1"

Last note: Mind that empty file isn't always empty:

• touch example.txt - this file is empty
• echo "" > example.txt - this file is NOT empty

My answer is somewhat specific for using with "virtual" file-systems like sysfs. Such kind of file-systems can give wrong results if you'll use the methods mentioned in most of answers here. Because a file can be stat'ed as having non-zero length, but if you try to read its contents you'll get nothing (or I/O error).

cat -n 1 '/path/to/file' &> /dev/null && echo true || echo false

A bit of explanation. Here we try to read the first line from the file and silently ignore its contents (send it to /dev/null). Depending on the exit status, we print "true" or "false".