1Str(3) OCaml library Str(3)
2
6 Str - Regular expressions and high-level string processing
7
9 Module Str
10
12 Module Str
13 : sig end
14 Regular expressions and high-level string processing
17 Regular expressions
25 type regexp
26 The type of compiled regular expressions.
29 val regexp : string -> regexp
33 Compile a regular expression. The following constructs are recognized:
35 - . Matches any character except newline.
37 - * (postfix) Matches the preceding expression zero, one or several
39 times
40 - + (postfix) Matches the preceding expression one or several times
42 - ? (postfix) Matches the preceding expression once or not at all
44 - [..] Character set. Ranges are denoted with - , as in [a-z] . An
46 initial ^ , as in [^0-9] , complements the set. To include a ] charac‐
47 ter in a set, make it the first character of the set. To include a -
48 character in a set, make it the first or the last character of the set.
49 - ^ Matches at beginning of line: either at the beginning of the
51 matched string, or just after a '\n' character.
52 - $ Matches at end of line: either at the end of the matched string, or
54 just before a '\n' character.
55 - \| (infix) Alternative between two expressions.
57 - \(..\) Grouping and naming of the enclosed expression.
59 - \1 The text matched by the first \(...\) expression ( \2 for the sec‐
61 ond expression, and so on up to \9 ).
62 - \b Matches word boundaries.
64 - \ Quotes special characters. The special characters are $^\.*+?[] .
66 In regular expressions you will often use backslash characters; it's
68 easier to use a quoted string literal {|...|} to avoid having to escape
69 backslashes.
70 For example, the following expression:
72 let r = Str.regexp {|hello \([A-Za-z]+\)|} in
73 Str.replace_first r {|\1|} "hello world"
74 returns the string "world" .
75 If you want a regular expression that matches a literal backslash char‐
77 acter, you need to double it: Str.regexp {|\\|} .
78 You can use regular string literals "..." too, however you will have
80 to escape backslashes. The example above can be rewritten with a regu‐
81 lar string literal as:
82 let r = Str.regexp "hello \\([A-Za-z]+\\)" in
83 Str.replace_first r "\\1" "hello world"
84 And the regular expression for matching a backslash becomes a quadruple
86 backslash: Str.regexp "\\\\" .
87 val regexp_case_fold : string -> regexp
91 Same as regexp , but the compiled expression will match text in a
93 case-insensitive way: uppercase and lowercase letters will be consid‐
94 ered equivalent.
95 val quote : string -> string
99 Str.quote s returns a regexp string that matches exactly s and nothing
102 else.
103 val regexp_string : string -> regexp
107 Str.regexp_string s returns a regular expression that matches exactly s
110 and nothing else.
111 val regexp_string_case_fold : string -> regexp
115 Str.regexp_string_case_fold is similar to Str.regexp_string , but the
118 regexp matches in a case-insensitive way.
119 String matching and searching
124 val string_match : regexp -> string -> int -> bool
125 string_match r s start tests whether a substring of s that starts at
128 position start matches the regular expression r . The first character
129 of a string has position 0 , as usual.
130 val search_forward : regexp -> string -> int -> int
134 search_forward r s start searches the string s for a substring matching
137 the regular expression r . The search starts at position start and pro‐
138 ceeds towards the end of the string. Return the position of the first
139 character of the matched substring.
140 Raises Not_found if no substring matches.
143 val search_backward : regexp -> string -> int -> int
147 search_backward r s last searches the string s for a substring matching
150 the regular expression r . The search first considers substrings that
151 start at position last and proceeds towards the beginning of string.
152 Return the position of the first character of the matched substring.
153 Raises Not_found if no substring matches.
156 val string_partial_match : regexp -> string -> int -> bool
160 Similar to Str.string_match , but also returns true if the argument
162 string is a prefix of a string that matches. This includes the case of
163 a true complete match.
164 val matched_string : string -> string
168 matched_string s returns the substring of s that was matched by the
171 last call to one of the following matching or searching functions:
172 - Str.string_match
174 - Str.search_forward
177 - Str.search_backward
180 - Str.string_partial_match
183 - Str.global_substitute
186 - Str.substitute_first
189 provided that none of the following functions was called in between:
191 - Str.global_replace
193 - Str.replace_first
196 - Str.split
199 - Str.bounded_split
202 - Str.split_delim
205 - Str.bounded_split_delim
208 - Str.full_split
211 - Str.bounded_full_split
214 Note: in the case of global_substitute and substitute_first , a call to
216 matched_string is only valid within the subst argument, not after
217 global_substitute or substitute_first returns.
218 The user must make sure that the parameter s is the same string that
220 was passed to the matching or searching function.
221 val match_beginning : unit -> int
225 match_beginning() returns the position of the first character of the
228 substring that was matched by the last call to a matching or searching
229 function (see Str.matched_string for details).
230 val match_end : unit -> int
234 match_end() returns the position of the character following the last
237 character of the substring that was matched by the last call to a
238 matching or searching function (see Str.matched_string for details).
239 val matched_group : int -> string -> string
243 matched_group n s returns the substring of s that was matched by the n
246 th group \(...\) of the regular expression that was matched by the last
247 call to a matching or searching function (see Str.matched_string for
248 details). When n is 0 , it returns the substring matched by the whole
249 regular expression. The user must make sure that the parameter s is
250 the same string that was passed to the matching or searching function.
251 Raises Not_found if the n th group of the regular expression was not
254 matched. This can happen with groups inside alternatives \| , options
255 ? or repetitions * . For instance, the empty string will match \(a\)*
256 , but matched_group 1 "" will raise Not_found because the first group
257 itself was not matched.
258 val group_beginning : int -> int
262 group_beginning n returns the position of the first character of the
265 substring that was matched by the n th group of the regular expression
266 that was matched by the last call to a matching or searching function
267 (see Str.matched_string for details).
268 Raises Not_found if the n th group of the regular expression was not
271 matched.
272 Raises Invalid_argument if there are fewer than n groups in the regular
275 expression.
276 val group_end : int -> int
280 group_end n returns the position of the character following the last
283 character of substring that was matched by the n th group of the regu‐
284 lar expression that was matched by the last call to a matching or
285 searching function (see Str.matched_string for details).
286 Raises Not_found if the n th group of the regular expression was not
289 matched.
290 Raises Invalid_argument if there are fewer than n groups in the regular
293 expression.
294 Replacement
299 val global_replace : regexp -> string -> string -> string
300 global_replace regexp templ s returns a string identical to s , except
303 that all substrings of s that match regexp have been replaced by templ
304 . The replacement template templ can contain \1 , \2 , etc; these se‐
305 quences will be replaced by the text matched by the corresponding group
306 in the regular expression. \0 stands for the text matched by the whole
307 regular expression.
308 val replace_first : regexp -> string -> string -> string
312 Same as Str.global_replace , except that only the first substring
314 matching the regular expression is replaced.
315 val global_substitute : regexp -> (string -> string) -> string ->
319 string
320 global_substitute regexp subst s returns a string identical to s , ex‐
323 cept that all substrings of s that match regexp have been replaced by
324 the result of function subst . The function subst is called once for
325 each matching substring, and receives s (the whole text) as argument.
326 val substitute_first : regexp -> (string -> string) -> string -> string
330 Same as Str.global_substitute , except that only the first substring
332 matching the regular expression is replaced.
333 val replace_matched : string -> string -> string
337 replace_matched repl s returns the replacement text repl in which \1 ,
340 \2 , etc. have been replaced by the text matched by the corresponding
341 groups in the regular expression that was matched by the last call to a
342 matching or searching function (see Str.matched_string for details). s
343 must be the same string that was passed to the matching or searching
344 function.
345 Splitting
350 val split : regexp -> string -> string list
351 split r s splits s into substrings, taking as delimiters the substrings
354 that match r , and returns the list of substrings. For instance, split
355 (regexp "[ \t]+") s splits s into blank-separated words. An occurrence
356 of the delimiter at the beginning or at the end of the string is ig‐
357 nored.
358 val bounded_split : regexp -> string -> int -> string list
362 Same as Str.split , but splits into at most n substrings, where n is
364 the extra integer parameter.
365 val split_delim : regexp -> string -> string list
369 Same as Str.split but occurrences of the delimiter at the beginning and
371 at the end of the string are recognized and returned as empty strings
372 in the result. For instance, split_delim (regexp " ") " abc " returns
373 [""; "abc"; ""] , while split with the same arguments returns ["abc"] .
374 val bounded_split_delim : regexp -> string -> int -> string list
378 Same as Str.bounded_split , but occurrences of the delimiter at the be‐
380 ginning and at the end of the string are recognized and returned as
381 empty strings in the result.
382 type split_result =
385 | Text of string
386 | Delim of string
387 val full_split : regexp -> string -> split_result list
393 Same as Str.split_delim , but returns the delimiters as well as the
395 substrings contained between delimiters. The former are tagged Delim
396 in the result list; the latter are tagged Text . For instance,
397 full_split (regexp "[{}]") "{ab}" returns [Delim "{"; Text "ab"; Delim
398 "}"] .
399 val bounded_full_split : regexp -> string -> int -> split_result list
403 Same as Str.bounded_split_delim , but returns the delimiters as well as
405 the substrings contained between delimiters. The former are tagged De‐
406 lim in the result list; the latter are tagged Text .
407 Extracting substrings
412 val string_before : string -> int -> string
413 string_before s n returns the substring of all characters of s that
416 precede position n (excluding the character at position n ).
417 val string_after : string -> int -> string
421 string_after s n returns the substring of all characters of s that fol‐
424 low position n (including the character at position n ).
425 val first_chars : string -> int -> string
429 first_chars s n returns the first n characters of s . This is the same
432 function as Str.string_before .
433 val last_chars : string -> int -> string
437 last_chars s n returns the last n characters of s .
440OCamldoc 2022-07-22 Str(3)