How to grep for tabs without using literal tabs and why does \t not work?

grep is using regular expressions as defined by POSIX. For whatever reasons POSIX have not defined \t as tab.

You have several alternatives:

• tell grep to use the regular expressions as defined by perl (perl has \t as tab):

  grep -P "\t" foo.txt
  

  the man page warns that this is an "experimental" feature. at least \t seems to work fine. but more advanced perl regex features may not.

• use printf to print a tab character for you:

  grep "$(printf '\t')" foo.txt
  

• use the literal tab character:

  grep "^V<tab>" foo.txt
  

  that is: type grep ", then press ctrl+v, then press tab, then type " foo.txt. pressing ctrl+v in the terminal causes the next key to be taken verbatim. that means the terminal will insert a tab character instead of triggering some function bound to the tab key.

• use the ansi c quoting feature of bash:

  grep $'\t' foo.txt
  

  this does not work in all shells.

• use awk:

  awk '/\t/'
  

• use sed:

  sed -n '/\t/p'
  

See the wikipedia article about regular expressions for an overview of the defined character classes in POSIX and other systems.

It is not exactly the answer you would want to hear, but a possible use of escape sequences is provided by bash

command | grep $'\t'

(do not put it into double quotes!).

awk '/\t/' is my favorite workaround:

printf 'a\t\nb' | awk '/\t/'

Output: a\t.