Info Catalog m4: Len m4: Text handling m4: Regexp

m4: Index macro

 
 11.2 Searching for substrings
 =============================
 
 Searching for substrings is done with 'index':
 
  -- Builtin: index (STRING, SUBSTRING)
      Expands to the index of the first occurrence of SUBSTRING in
      STRING.  The first character in STRING has index 0.  If SUBSTRING
      does not occur in STRING, 'index' expands to '-1'.
 
      The macro 'index' is recognized only with parameters.
 
      index(`gnus, gnats, and armadillos', `nat')
      =>7
      index(`gnus, gnats, and armadillos', `dag')
      =>-1
 
    Omitting SUBSTRING evokes a warning, but still produces output;
 contrast this with an empty SUBSTRING.
 
      index(`abc')
      error->m4:stdin:1: Warning: too few arguments to builtin `index'
      =>0
      index(`abc', `')
      =>0
      index(`abc', `b')
      =>1
 

Info Catalog m4: Len m4: Text handling m4: Regexp