Learning Perl: 8.9. A Pattern Test Program

 

@H_404_23@

8.9. A Pattern Test Program

When in the course of Perl events it becomes necessary for a programmer to write a regular expression,it may be difficult to tell what the pattern will do. It's normal to find that a pattern matches more than you expected,or less. Or it may match earlier in the string than you expected,or later,or not at all.

This program is useful to test out a pattern on some strings and see what it matches and where:

    #!/usr/bin/perl
    while (<>) {                   # take one input line at a time
      chomp;
      if (/YOUR_PATTERN_GOES_HERE/) {
        print "Matched: |$`<$&>$'|/n";  # the special match vars
      } else {
        print "No match: |$_|/n";
      }
    }

This pattern test program is written for programmers and not end users to use,you can tell because it doesn't have any prompts or usage @R_190_4045@ion. It will take any number of input lines and check each one against the pattern that you'll put in place of the string saying YOUR_PATTERN_GOES_HERE. For each line that matches,it uses the three special match variables ($`,$&,and $') to make a picture of where the match happened. What you'll see is this: if the pattern is /match/ and the input is beforematchafter,the output will say "|before<match>after|",using angle brackets to show you what part of the string was matched by your pattern. If your pattern matches something you didn't expect,you'll see it right away.