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

You have several alternatives:

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

  
  
  

  grep -P "	" foo.txt
  
  

  
  
  

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




• use printf to print a tab character for you:

  
  
  

  grep "$(printf '	')" 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 $'	' foo.txt
  
  

  
  
  

  this does not work in all shells.




• use awk:

  
  
  

  awk '/	/'
  
  




• use sed:

  
  
  

  sed -n '/	/p'
  
  

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