Contents

1. What Is Perl? 2. Course Requisites and Goals 3. Perl References & Resources 4. State of Perl 5. Taste of Perl 6. Storing & Running Perl Programs 7. The Elements 8. Literals & Operators

9. Loops and I/O 10. Grade Book Example 11. Pipe I/O and System Calls 12. Matching 13. Parsing 14. Simple CGI 15. Testing Perl Programs 16. Common Goofs

13. Parsing

See the Perl Reference Guide section 14, Search and replace functions. When you include parenthesis ( ) in a matched string, the matching text in the parenthesis may subsequently be referenced via variables $1, $2, $3, ... for each left parenthesis encountered. These matches can also be assigned as sequential values of an array.

    #!/usr/local/bin/perl -w

    $s = 'There is 1 date 10/25/95 in here somewhere.';

    print "\$s=$s\n";

    $s =~ /(\d{1,2})\/(\d{1,2})\/(\d{2,4})/;

    print "Trick 1: \$1=$1, \$2=$2, \$3=$3,\n",

	  "         \$\`=",$`," \$\'=",$',"\n";

    

    ($mo, $day, $year) =

        ( $s =~ /(\d{1,2})\/(\d{1,2})\/(\d{2,4})/ );

    print "Trick 2: \$mo=$mo, \$day=$day, \$year=$year.\n";

    

    ($wholedate,$mo, $day, $year) =

        ( $s =~ /((\d{1,2})\/(\d{1,2})\/(\d{2,4}))/ );

    print "Trick 3: \$wholedate=$wholedate, \$mo=$mo, ",

        "\$day=$day, \$year=$year.\n";

Results of above:

    $s=There is 1 date 10/25/95 in here somewhere.

    Trick 1: $1=10, $2=25, $3=95,

             $`=There is 1 date  $'= in here somewhere.

    Trick 2: $mo=10, $day=25, $year=95.

    Trick 3: $wholedate=10/25/95, $mo=10, $day=25, $year=95.

Note that when patterns are matched in an array context as in Tricks 2 and 3, $1, $2, ..., and $`, $', and $& are not set.

Regular expressions are greedy. In the following example we try to match whatever is between "<" and ">" :

    #!/usr/local/bin/perl -w

    $s = 'Beware of <STRONG>greedy</strong> regular expressions.';

    print "\$s=$s\n";

    ($m) = ( $s =~ /<(.*)>/ );

    print "Try 1: \$m=$m\n";

    ($m) = ( $s =~ /<([^>]*)>/ );

    print "Try 2: \$m=$m\n";

This results in:

    $s=Beware of <STRONG>greedy</strong> regular expressions.

    Try 1: $m=STRONG>greedy</strong

    Try 2: $m=STRONG

Homework: Parsing and Reporting

1. See preceding "Grade Book" example. Using the same "stufile" input, print a list of students ordered by family name, with any quoted nickname listed in place of the given name, and family name last. Produce output like this:

    Student-ID  Year  Name

    357913      JR    Thomas Jefferson

    246802      SO    Abe Lincoln

    212121      SO    Teddy Roosevelt

    123456      SR    George Washington