The str library: regular expressions and string processing

The str library provides high-level string processing functions, some based on regular expressions. It is intended to support the kind of file processing that is usually performed with scripting languages such as awk, perl or sed.

Unix:

Programs that use the str library must be linked in ``custom runtime'' mode, as follows:

        ocamlc -custom other options str.cma other files -cclib -lstr
        ocamlopt other options str.cmxa other files -cclib -lstr

For interactive use of the str library, do:

        ocamlmktop -custom -o mytop str.cma -cclib -lstr
        ./mytop

Windows:

Programs that use the str library must be linked in ``custom runtime'' mode, as follows:

        ocamlc -custom other options str.cma other files %CAMLLIB%/libstr.lib
        ocamlopt other options str.cmxa other files %CAMLLIB%/libstr.lib

For interactive use of the str library, do:

        ocamlmktop -custom -o mytop.exe str.cma %CAMLLIB%/libstr.lib
        ./mytop.exe

Module Str: regular expressions and high-level string processing

Regular expressions

type regexp

The type of compiled regular expressions.

val regexp: string -> regexp

Compile a regular expression. The syntax for regular expressions is the same as in Gnu Emacs. The special characters are $^.*+?[]]. The following constructs are recognized: \\\verb. ` matches any character except newline
* (postfix) matches the previous expression zero, one or several times
+ (postfix) matches the previous expression one or several times
? (postfix) matches the previous expression once or not at all
[..] character set; ranges are denoted with -, as in a-z; an initial ^, as in ^0-9, complements the set
^ matches at beginning of line
$ matches at end of line
\| (infix) alternative between two expressions
\(..\) grouping and naming of the enclosed expression
\1 the text matched by the first \(...\) expression (\2 for the second expression, etc)
\b matches word boundaries
\ quotes special characters.

val regexp_case_fold: string -> regexp

Same as regexp, but the compiled expression will match text in a case-insensitive way: uppercase and lowercase letters will be considered equivalent.

String matching and searching

val string_match: regexp -> string -> int -> bool

string_match r s start tests whether the characters in s starting at position start match the regular expression r. The first character of a string has position 0, as usual.

val search_forward: regexp -> string -> int -> int

search_forward r s start searchs the string s for a substring matching the regular expression r. The search starts at position start and proceeds towards the end of the string. Return the position of the first character of the matched substring, or raise Not_found if no substring matches.

val search_backward: regexp -> string -> int -> int

Same as search_forward, but the search proceeds towards the beginning of the string.

val matched_string: string -> string

matched_string s returns the substring of s that was matched by the latest string_match, search_forward or search_backward. The user must make sure that the parameter s is the same string that was passed to the matching or searching function.

val match_beginning: unit -> int
val match_end: unit -> int

match_beginning() returns the position of the first character of the substring that was matched by string_match, search_forward or search_backward. match_end() returns the position of the character following the last character of the matched substring.

val matched_group: int -> string -> string

matched_group n s returns the substring of s that was matched by the nth group \(...\) of the regular expression during the latest string_match, search_forward or search_backward. The user must make sure that the parameter s is the same string that was passed to the matching or searching function.

val group_beginning: int -> int
val group_end: int -> int

group_beginning n returns the position of the first character of the substring that was matched by the nth group of the regular expression. group_end n returns the position of the character following the last character of the matched substring.

Replacement

val global_replace: regexp -> string -> string -> string

global_replace regexp repl s returns a string identical to s, except that all substrings of s that match regexp have been replaced by repl. The replacement text repl can contain \1, \2, etc; these sequences will be replaced by the text matched by the corresponding group in the regular expression. \0 stands for the text matched by the whole regular expression.

val replace_first: regexp -> string -> string -> string

Same as global_replace, except that only the first substring matching the regular expression is replaced.

val global_substitute: regexp -> (string -> string) -> string -> string

global_substitute regexp subst s returns a string identical to s, except that all substrings of s that match regexp have been replaced by the result of function subst. The function subst is called once for each matching substring, and receives s (the whole text) as argument.

val substitute_first: regexp -> (string -> string) -> string -> string

Same as global_substitute, except that only the first substring matching the regular expression is replaced.

Splitting

val split: regexp -> string -> string list

split r s splits s into substrings, taking as delimiters the substrings that match r, and returns the list of substrings. For instance, split (regexp "[ \t]+") s splits s into blank-separated words.

val bounded_split: regexp -> string -> int -> string list

Same as split, but splits into at most n substrings, where n is the extra integer parameter.

Extracting substrings

val string_before: string -> int -> string

string_before s n returns the substring of all characters of s that precede position n (excluding the character at position n).

val string_after: string -> int -> string

string_after s n returns the substring of all characters of s that follow position n (including the character at position n).

val first_chars: string -> int -> string

first_chars s n returns the first n characters of s. This is the same function as string_before.

val last_chars: string -> int -> string

last_chars s n returns the last n characters of s.