Regular Expressions

(This help text is largely from TinyMUSH 2.2.4, with permission)

SharpMUSH regular expressions use the .NET engine. When porting PennMUSH code, check regexp syntax and regexp classes for PCRE and POSIX syntax differences.

The majority of matching in MUSH is done with wildcard (“globbing”) patterns. There is a second type of matching, using regular expressions, that is available in certain circumstances.

For attributes that are $-commands or ^-listen-patterns, setting that attribute “regexp” (with ‘@set <object>/<attribute>=regexp’) causes patterns to be matched using regular expressions rather than globbing. In addition, the function regmatch() performs regular expression matching.

In a REGEXP command or listen match, the substring of the string which matched the regexp pattern is %0; %1 through %9 are the substrings of the string which matched parenthesized expressions within the regexp pattern.

Data validation examples

Regular expressions are extremely useful when you want to enforce a data type. For example, if you have a command where you want a player to enter a string and a number (‘+setnum <player>=<number>’, for example), you might do it like this:

    > &DO_NUM Command Object=$^\+setnum (.+)=([0-9]+)$: @va me=Data: %1 = %2
    > @set Command Object/DO_NUM=regexp

Then, ‘+setnum cookies=30’ would set VA to “Data: cookies = 30”. This eliminates your having to check to see if the player entered a number, since the regular expression matches only numbers. Furthermore, the ’+’ guarantees that there needs to be at least one character there, so a player can’t enter ‘+setnum cookies=’ or ‘+setnum =10’ or similarly malformed input.

The ’+’ sign in the command has to be escaped out, or it is taken as a regexp token. Furthermore, the pattern-match has to be anchored with ^ and $, or something like ‘try +setnum cookies=30 now’ would also match.

However, keep in mind that players who attempt to use the command and give invalid input (such as “+setnum cookies=thirty”) will receive the normal, non-descriptive Huh? message. Using a broader match and validating the input in softcode, so you can give more descriptive error messages, may be desirable.

Regular expression syntax is explained in regexp syntax.