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How to check if a large file contains only zero bytes ('\0') in Linux using a shell command? I can write a small program for this but this seems to be an overkill.
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You can use the find command and other options as follows. The -s option to the test builtin check to see if FILE exists and has a size greater than zero. It returns true and false values to indicate that file is empty or has some data.
If you just want to get a list of zero byte sized files, remove the -exec and -delete options. This will cause find to print out the list of empty files.
$? is the exit status of the most recently-executed command; by convention, 0 means success and anything else indicates failure. That line is testing whether the grep command succeeded. The grep manpage states: The exit status is 0 if selected lines are found, and 1 if not found.
If you're using bash, you can use read -n 1 to exit early if a non-NUL character has been found:
<your_file tr -d '\0' | read -n 1 || echo "All zeroes."
where you substitute the actual filename for your_file.
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The "file" /dev/zero returns a sequence of zero bytes on read, so a cmp file /dev/zero should give essentially what you want (reporting the first different byte just beyond the length of file).
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