Match on Groups in Regular Expressions using the Standard Library
Task
Text Processing / Regular Expressions / Match on Groups in Regular Expressions
Use Regexp to parse a YYYY-MM-DD date.
No packages used
This recipe uses only the OCaml Standard Library.Code
Define a regular expression pattern to match dates in YYYY-MM-DD format
The {re|...|re} syntax lets us write the pattern without escaping slashes
The \(...\) groups capture parts of the match we want to extract later:
- First group: year (digits)
- Second group: month (digits)
- Third group: day (digits)
let regexp =
Str.regexp {re|\([0-9]+\)-\([0-9]+\)-\([0-9]+\)|re}
Extract the matched groups (year, month, day) from the string
After a successful Str.search_forward, we use
Str.matched_group to get the individual values for the matching groups.
Note: matched_group 0 would return the entire matched string
let () =
let str = "Date: 1971-01-23" in
let _index = Str.search_forward regexp str 0 in
let year = Str.matched_group 1 str
and month = Str.matched_group 2 str
and day = Str.matched_group 3 str in
Printf.printf "year=%s, month=%s, day=%s\n" year month day
Discussion
If you want to run this example in UTop, you need to run #require "str";;
in order to load the Str module into UTop.