Regular expressions and high-level string processing
Module Str
Module Str : sig end
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 following constructs are recognized:
- . Matches any character except newline.
- * (postfix) Matches the preceding expression zero, one or several times
- + (postfix) Matches the preceding expression one or several times
- ? (postfix) Matches the preceding 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. To include a ] character in a set, make it the first character of the set. To include a - character in a set, make it the first or the last character of the set.
- ^ Matches at beginning of line (either at the beginning of the matched string, or just after a newline character).
- $ Matches at end of line (either at the end of the matched string, or just before a newline character).
- \(rs| (infix) Alternative between two expressions.
- \(rs(..\(rs) Grouping and naming of the enclosed expression.
- \(rs1 The text matched by the first \(rs(...\(rs) expression ( \(rs2 for the second expression, and so on up to \(rs9 ).
- \(rsb Matches word boundaries.
- \(rs Quotes special characters. The special characters are $^\(rs.*+?[] .
Note: the argument to regexp is usually a string literal. In this case, any backslash character in the regular expression must be doubled to make it past the OCaml string parser. For example, the following expression: let r = Str.regexp hello \(rs\(rs([A-Za-z]+\(rs\(rs) in Str.replace_first r \(rs\(rs1 hello world returns the string world .
In particular, if you want a regular expression that matches a single backslash character, you need to quote it in the argument to regexp (according to the last item of the list above) by adding a second backslash. Then you need to quote both backslashes (according to the syntax of string constants in OCaml) by doubling them again, so you need to write four backslash characters: Str.regexp \(rs\(rs\(rs\(rs .
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.
val quote : string -> string
Str.quote s returns a regexp string that matches exactly s and nothing else.
val regexp_string : string -> regexp
Str.regexp_string s returns a regular expression that matches exactly s and nothing else.
val regexp_string_case_fold : string -> regexp
Str.regexp_string_case_fold is similar to Str.regexp_string , but the regexp matches in a case-insensitive way.
=== String matching and searching ===
val string_match : regexp -> string -> int -> bool
string_match r s start tests whether a substring of s that starts at position start matches 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 searches 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.
Raises Not_found if no substring matches.
val search_backward : regexp -> string -> int -> int
search_backward r s last searches the string s for a substring matching the regular expression r . The search first considers substrings that start at position last and proceeds towards the beginning of string. Return the position of the first character of the matched substring.
Raises Not_found if no substring matches.
val string_partial_match : regexp -> string -> int -> bool
Similar to Str.string_match , but also returns true if the argument string is a prefix of a string that matches. This includes the case of a true complete match.
val matched_string : string -> string
matched_string s returns the substring of s that was matched by the last call to one of the following matching or searching functions:
- Str.string_match
- Str.search_forward
- Str.search_backward
- Str.string_partial_match
- Str.global_substitute
- Str.substitute_first provided that none of the following functions was called inbetween:
- Str.global_replace
- Str.replace_first
- Str.split
- Str.bounded_split
- Str.split_delim
- Str.bounded_split_delim
- Str.full_split
- Str.bounded_full_split
Note: in the case of global_substitute and substitute_first , a call to matched_string is only valid within the subst argument, not after global_substitute or substitute_first returns.
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
match_beginning() returns the position of the first character of the substring that was matched by the last call to a matching or searching function (see Str.matched_string for details).
val match_end : unit -> int
match_end() returns the position of the character following the last character of the substring that was matched by the last call to a matching or searching function (see Str.matched_string for details).
val matched_group : int -> string -> string
matched_group n s returns the substring of s that was matched by the n th group \(rs(...\(rs) of the regular expression that was matched by the last call to a matching or searching function (see Str.matched_string for details). The user must make sure that the parameter s is the same string that was passed to the matching or searching function.
Raises Not_found if the n th group of the regular expression was not matched. This can happen with groups inside alternatives \(rs| , options ? or repetitions * . For instance, the empty string will match \(rs(a\(rs)* , but matched_group 1 will raise Not_found because the first group itself was not matched.
val group_beginning : int -> int
group_beginning n returns the position of the first character of the substring that was matched by the n th group of the regular expression that was matched by the last call to a matching or searching function (see Str.matched_string for details).
Raises
Not_found if the n th group of the regular expression was not matched.
Invalid_argument if there are fewer than n groups in the regular expression.
val group_end : int -> int
group_end n returns the position of the character following the last character of substring that was matched by the n th group of the regular expression that was matched by the last call to a matching or searching function (see Str.matched_string for details).
Raises
Not_found if the n th group of the regular expression was not matched.
Invalid_argument if there are fewer than n groups in the regular expression.
=== Replacement ===
val global_replace : regexp -> string -> string -> string
global_replace regexp templ s returns a string identical to s , except that all substrings of s that match regexp have been replaced by templ . The replacement template templ can contain \(rs1 , \(rs2 , etc; these sequences will be replaced by the text matched by the corresponding group in the regular expression. \(rs0 stands for the text matched by the whole regular expression.
val replace_first : regexp -> string -> string -> string
Same as Str.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 Str.global_substitute , except that only the first substring matching the regular expression is replaced.
val replace_matched : string -> string -> string
replace_matched repl s returns the replacement text repl in which \(rs1 , \(rs2 , etc. have been replaced by the text matched by the corresponding groups in the regular expression that was matched by the last call to a matching or searching function (see Str.matched_string for details). s must be the same string that was passed to the matching or searching function.
=== 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 [ \(rst]+ ) s splits s into blank-separated words. An occurrence of the delimiter at the beginning or at the end of the string is ignored.
val bounded_split : regexp -> string -> int -> string list
Same as Str.split , but splits into at most n substrings, where n is the extra integer parameter.
val split_delim : regexp -> string -> string list
Same as Str.split but occurrences of the delimiter at the beginning and at the end of the string are recognized and returned as empty strings in the result. For instance, split_delim (regexp ) abc returns [""; abc ; ] , while split with the same arguments returns ["abc"] .
val bounded_split_delim : regexp -> string -> int -> string list
Same as Str.bounded_split , but occurrences of the delimiter at the beginning and at the end of the string are recognized and returned as empty strings in the result.
type split_result = | Text of string | Delim of string
val full_split : regexp -> string -> split_result list
Same as Str.split_delim , but returns the delimiters as well as the substrings contained between delimiters. The former are tagged Delim in the result list; the latter are tagged Text . For instance, full_split (regexp [{}] ) {ab} returns [Delim { ; Text ab ; Delim } ] .
val bounded_full_split : regexp -> string -> int -> split_result list
Same as Str.bounded_split_delim , but returns the delimiters as well as the substrings contained between delimiters. The former are tagged Delim in the result list; the latter are tagged Text .
=== 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 Str.string_before .
val last_chars : string -> int -> string
last_chars s n returns the last n characters of s .