I am trying to use grep to find the string "crk" in a file. I know the string exists in a c source file in the form

kop.crk_op = CRK_MOD_EXP;

However, when I search using

 grep -rnw --include '*.c' '.' -e "crk"

I get an empty result. The line

 grep -rnw --include '*.c' '.' -e "crk_op"

works just fine, but that really isn't helpful to me. I assume the '_' character is somehow messing up my search. How can I modify my approach to match all strings of which "crk" is a substring, even when the '_' character is present, or any other character for that matter?

Edit: It seems I got a bit trigger happy on this post. The command

grep -rnw --include '*.c' '.' -e "[^ ]*crk[^ ]*"

seems to work. Alternatively, can someone explain why the extra wildcards are needed?

1 Answer 1


The -w option makes grep look for words, so it will show crk when surrounded by non-word characters. From man grep:

-w, --word-regexp
      Select  only  those  lines  containing  matches  that form whole
      words.  The test is that the matching substring must  either  be
      at  the  beginning  of  the  line,  or  preceded  by  a non-word
      constituent character.  Similarly, it must be either at the  end
      of  the  line  or  followed by a non-word constituent character.
      Word-constituent  characters  are  letters,  digits,   and   the

_ is a word character, so crk_op will not match crk with -w.

The convoluted regex "[^ ]*crk[^ ]*" works because it allows any number of non-space characters between the word boundaries that grep requires.

Just do:

grep -rn --include '*.c' . -e crk

You don't need to qoute . for the current directory there.

  • Hmmm, so '_' is a word character but '[', for example, is not. How odd...
    – Aroto
    Apr 5, 2017 at 5:43
  • @user3813122 not particularly so, if you know a but of programming history. _ has been allowed in variable names since around the time grep was created (at least), and it's only natural to see a variable name as a word.
    – muru
    Apr 5, 2017 at 5:45

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