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Available inall subroutines.

Replaces the first occurrence of pattern (a Perl-compatible regular expression) in input with replacement. If no match is found, no replacement is made. Calls to regsub do not set re.group.*.

Groups captured in pattern can be inserted into the replacement string with \1 through \9, which correspond to their re.group.* counterparts. Following numeric literals are not interpreted. Captures can also be specified as \{1} through \{19} which will allow you to specify ones higher than 9. It is advisable to use non-capturing groups with (?:) if the sub-pattern is not used in a backreference.

Errors

This function may fail to make a replacement if the regular expression recurses too heavily. Such a situation may occur with lookahead and lookbehind assertions, or other recursing non-regular expressions. In this case, fastly.error is set to EREGRECUR.

Example

The following example deletes the query string portion of the request URL (equivalent to req.url.path):

set req.url = regsub(req.url, "\?.*$", "");

This replaces the last two digits of an HTTP status code to 00 for grouping purposes. Note that the 00 remains as a literal "00" in the substitution:

set var.response_code_type = regsub(beresp.status, "^([1-5])..", "\100"); # capture group \1 followed by literal 00

This will reverse the first 15 characters of a header:

set var.reversed = regsub(req.http.longheader, "(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)", "\{15}\{14}\{13}\{12}\{11}\{10}\9\8\7\6\5\4\3\2\1");

Try it out

regsub is used in the following code examples. Examples apply VCL to real-world use cases and can be deployed as they are, or adapted for your own service. See the full list of code examples for more inspiration.

Click RUN on a sample below to provision a Fastly service, execute the code on Fastly, and see how the function behaves.