I used the below command but it doesn't work.

grep "^@^@^@" *

migrated from stackoverflow.com Nov 18 '12 at 12:02

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You can grep for any characters including control/non-printable characters in perl-regexp mode (-P) by its hex code:

grep -Pa '\x00' ...
  • 5
    You might want to add -a option, otherwise grep thinks it is binary data and won't display the matching lines. – mpy Jun 26 '13 at 15:19
  • I can't find a way to check if file contains only ASCII=0 bytes... grep -Pv '\x00' file does not work in Cygwin... – pbies Aug 16 '18 at 12:51

^@ is not a carat ^ and at-sign @, it's one character. It's how some programs display the NUL character—ASCII value 0, also known as \0 in C.

Here I've created a file with a NUL byte in it. Notice that I use cat -v to show non-printing characters.

$ cat -v blah
$ hexdump -C blah
00000000  68 65 6c 6c 6f 0a 6e 75  6c 6c 00 0a 68 69 0a     |hello.null..hi.|

Grep has trouble finding NULs since they're used to terminate strings in C. Sed, however, can do the job:

$ sed -n '/\x0/p' blah
$ sed -n '/\x0/p' blah | cat -v

In vi, in insert mode press Ctrl-V, Ctrl-Shift-@ to insert a null byte.


If grep -P doesn't work (e.g. on OS X), try this:

grep -E '\x00' ...
  • Are you sure that this works? I does not with my version: grep (GNU grep) 2.14 – guettli Nov 20 '17 at 7:19
  • 3
    This answer is for BSD grep, try the top answer for GNU grep: grep -Pa '\x00' ... – robinst Nov 22 '17 at 3:18

In bash you can add special characters when prefixed with C-q or C-v. So you can, for example

grep 'Ctrl-vCtrl-a' file.txt

The search string should be read as control key + character v, followed by control key + character a, which searches for ASCII value SOH (01). Unfortunately this doesn't work for the NUL character.

  • Presumably you don't actually mean that such a character sequence should be written out literally, but instead entered on the keyboard logically? – Lightness Races in Orbit Nov 17 '12 at 22:10
  • Yes, of course. This is control key held down, press v, then hold down Control key, press a. – Olaf Dietsche Nov 17 '12 at 22:12
  • I think that's unclear in your answer. – Lightness Races in Orbit Nov 17 '12 at 22:13
  • @LightnessRacesinOrbit Thanks for the hint. I tried to clarify in the answer. – Olaf Dietsche Nov 17 '12 at 22:15
  • @JohnKugelman Thanks for the edit. Seems I should have looked into the help more closely. – Olaf Dietsche Nov 17 '12 at 22:18

^@ is the NUL character. What do you want to do with the lines of your files containing it ?

You could have a look at https://stackoverflow.com/questions/2398393/identifying-and-removing-null-characters-in-unix which deals with a similar issue.


Character ^@ is the NUL char, so I'm afraid that it cannot be grepped directly.

Your best option would be probably to write a simple program that searches for this sequence of bytes.

Alternatively you may try to convert it into some form of hexadecimal dump (od, xxd or so) and grep into the output of it. But frankly speaking, it would be tricky to get it right.

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