(m4) Index

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(m4) Regexp

 
 Searching for substrings
 ========================
 
    Searching for substrings is done with `index':
 
      index(STRING, SUBSTRING)
 
 which 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'.
 
      index(`gnus, gnats, and armadillos', `nat')
      =>7
      index(`gnus, gnats, and armadillos', `dag')
      =>-1
 
    The builtin macro `index' is recognized only when given arguments.
 

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