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