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.

Programs that use the str library must be linked as follows:

        nmlc other options str.cma other files
        nmlo other options str.cmxa other files

For interactive use of the str library, do:

        ntopgen -o mytop str.cma
        ./mytop

or (if dynamic linking of C libraries is supported on your platform), start nml and type #load "str.cma";;.

Module Str

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:

. 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.

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 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 Str.search_forward, but the search proceeds towards the beginning of the string.

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

Similar to Str.string_match, but succeeds whenever 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 latest Str.string_match, Str.search_forward or Str.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

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

val match_end : unit -> int

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

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 Str.string_match, Str.search_forward or Str.search_backward. The user must make sure that the parameter s is the same string that was passed to the matching or searching function. matched_group n s raises Not_found if the nth 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 nth group of the regular expression.
Raises Not_found if the nth group of the regular expression was not matched.

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 nth group of the regular expression.
Raises Not_found if the nth group of the regular expression was not matched.

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 most recent matching operation. s must be the same string that was matched during this matching operation.

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 and 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. For instance, split_delim (regexp " ") " abc " returns [""; "abc"; ""], while split with the same arguments returns ["abc"].

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. For instance, full_split (regexp "[{}]") "{ab}" returns [Delim "{"; Text "ab"; Delim "}"].

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.