--- name: "Str" section: "3o" platform: "linux" package: "ocaml" version: "5.5.0-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/Str" --- # Str(3o) Regular expressions and high-level string processing ## NAME Str - Regular expressions and high-level string processing ## Module Module Str ## Documentation Module **Str**\ : **sig end** Regular expressions and high-level string processing ### Regular expressions The **Str** library provides regular expressions on sequences of bytes. It is, in general, unsuitable to match Unicode characters. *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 '\\n' character. \- **$** Matches at end of line: either at the end of the matched string, or just before a '\\n' character. \- **\\\|** (infix) Alternative between two expressions. \- **\\(..\\)** Grouping and naming of the enclosed expression. \- **\\1** The text matched by the first **\\(...\\)** expression ( **\\2** for the second expression, and so on up to **\\9** ). \- **\\b** Matches word boundaries. \- **\\** Quotes special characters. The special characters are **$^\\.\*+?\[\]** . In regular expressions you will often use backslash characters; it's easier to use a quoted string literal **{\|...\|}** to avoid having to escape backslashes. For example, the following expression: ``` let r = Str.regexp {|hello \([A-Za-z]+\)|} in Str.replace_first r {|\1|} "hello world" ``` returns the string **"world"** . If you want a regular expression that matches a literal backslash character, you need to double it: **Str.regexp {\|\\\\\|}** . You can use regular string literals **"..."** too, however you will have to escape backslashes. The example above can be rewritten with a regular string literal as: ``` let r = Str.regexp "hello \\([A-Za-z]+\\)" in Str.replace_first r "\\1" "hello world" ``` And the regular expression for matching a backslash becomes a quadruple backslash: **Str.regexp "\\\\\\\\"** . *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 in between: \- **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 **\\(...\\)** of the regular expression that was matched by the last call to a matching or searching function (see **Str.matched\_string** for details). When **n** is **0** , it returns the substring matched by the whole regular expression. 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 **\\\|** , options **?** or repetitions **\*** . For instance, the empty string will match **\\(a\\)\*** , 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. **Raises 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. **Raises 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 **\\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 **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 **\\1** , **\\2** , 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 "\[ \\t\]+") 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** .