In addition to Mumps 95 pattern matching using the '?' operator, it is also possible to perform pattern matching against Perl regular expressions via the perlmatch function. Support for this functionality is provided by the Perl-Compatible Regular Expressions library (PCRE), which supports a majority of the functionality found in Perl's regular expression engine.

The perlmatch function works in a somewhat similar fashion to the '?' operator. It is provided with a subject string and a Perl pattern against which to match the subject. The result of the function is boolean and may be used in boolean expression contexts such as the "If" statement.

1. A Mumps match expects that the pattern will match against the entire subject string, in that successful matching implies that no characters are left unmatched even if the pattern matched against an initial segment of the subject string. Using perlmatch, it is sufficient that the entire Perl pattern matches an initial segment of the subject string to return a successful match.

2. The perlmatch function has the side effect of creating variables in the local symbol table to hold backreferences, the equivalent concept of $1, $2, $3, ... in Perl. Up to nine backreferences are currently supported, and can be accessed through the same naming scheme as Perl ($1 through $9). These variables remain defined up to a subsequent call to perlmatch , at which point they are replaced by the backreferences captured from that invocation. Undefined backreferences are cleared between invocations; that is, if a match operation captured five backreferences, then $6 through $9 will contain the null string.

Examples

This program asks the user to input a telephone number. If the data entered looks like a valid telephone number, it extracts and prints the area code portion using a backreference; otherwise, it prints a failure message and exits.

   Zmain

   Write "Please enter a telephone number:",!
   Read phonenum

   If $$^perlmatch(phonenum,"^(1-)?(\(?\d{3}\)?)?(-| )?\d{3}-?\d{4}$") Do
   . Write "+++ This looks like a phone number.",!
   . Write "The area code is: ",$2,!
   Else  Do
   . Write "--- This didn't look like a phone number.",!

   Halt

The output of several sample runs of the program follows:

Please enter a telephone number:
1-123-555-4567
+++ This looks like a phone number.
The area code is: 123


Please enter a telephone number:
(123)-555-1234
+++ This looks like a phone number.
The area code is: (123)


Please enter a telephone number:
(123) 555-0987
+++ This looks like a phone number.
The area code is: (123)

As in Perl, sections of the regular expression contained in parentheses define what is contained in the backreferences following a match operation. The backreference variables are named in a left-to-right order with respect to the expression, meaning that $1 is assigned the portion matched against the leftmost parenthesized section of the regular expression, with further references assigned names in increasing order. For a much more in-depth treatment of the subject of Perl regular expressions, refer to the perlre manpage distributed with the Perl language (also widely available online).