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Stepping through regular expressions
More on Character Strings example from a Well House Consultants training course
More on More on Character Strings [link]

This example is described in the following article(s):
   • Object Orientation in an hour and other Perl Lectures - [link]

Source code: reg Module: P212
# Stepping through regular expressions

print ("What is your postcode ");
$pc = <STDIN> ;

# Longwinded but straightforward starting point:
if ($pc =~ /^[A-Z]{1,2}[0-9]{1,2} {1,}[0-9]{1}[A-Z]{2}$/) {
        print ("Yay\n");
} else {
        print ("Nah\n");
}

# Using capture parenthesis notation to store interesting bits
if ($pc =~ /^(([A-Z]{1,2})[0-9]{1,2}) {1,}([0-9]{1}[A-Z]{2})$/) {
        print ("Yay - $1 area $2 super, $3 outbound\n");
} else {
        print ("Nah\n");
}

# Storing results into named variables using list context
if (($area, $sup, $out) = $pc =~ /^(([A-Z]{1,2})[0-9]{1,2}) {1,}([0-9]{1}[A-Z]{2})$/) {
        print ("Yay - We have $area $sup and $out\n");
} else {
        print ("Nah\n");
}

# Also capturing the bits before and after the actual match
if (($area, $sup, $out) = $pc =~ /(([A-Z]{1,2})[0-9]{1,2}) {1,}([0-9]{1}[A-Z]{2})/) {
        print ("Yay - We have $area $sup and $out\n");
        print ("The bits are ... $& and $` and $'\n");
} else {
        print ("Nah\n");
}

# Using shortands such as \s and \d (remember \w \W \S and \D too)
if (($area, $sup, $out) = $pc =~ /(([A-Z]{1,2})\d{1,2})\s{1,}(\d{1}[A-Z]{2})/) {
        print ("Yay - We have $area $sup and $out\n");
        print ("The bits are ... $& and $` and $'\n");
} else {
        print ("Nah\n");
}

# Using posix style ... and a modifier too (x) to split regex across several lines
if (($area, $sup, $out) = $pc =~ /(([[:alpha:]]{1,2})[[:digit:]][[:alnum:]]?)
                                [[:space:]]+
                                ([[:digit:]][[:alpha:]]{2})/x) {
        print ("Yay - Longwinded We have $area $sup and $out\n");
        print ("The bits are ... $& and $` and $'\n");
} else {
        print ("Nah\n");
}
__END__

Sample Output

wizard:lf graham$ perl reg
What is your postcode SN12 6QL
Yay
Yay - SN12 area SN super, 6QL outbound
Yay - We have SN12 SN and 6QL
Yay - We have SN12 SN and 6QL
The bits are ... SN12 6QL and and

Yay - We have SN12 SN and 6QL
The bits are ... SN12 6QL and and

Yay - Longwinded We have SN12 SN and 6QL
The bits are ... SN12 6QL and and

wizard:lf graham$ perl reg
What is your postcode We are at SN12 7NY at the hotel
Nah
Nah
Nah
Yay - We have SN12 SN and 7NY
The bits are ... SN12 7NY and We are at and at the hotel

Yay - We have SN12 SN and 7NY
The bits are ... SN12 7NY and We are at and at the hotel

Yay - Longwinded We have SN12 SN and 7NY
The bits are ... SN12 7NY and We are at and at the hotel

wizard:lf graham$

Learn about this subject
This module and example are covered on the following public courses:
 * Perl Programming
 * Perl bootcamp
 * Learning to program in Perl
 * Perl Programming
Also available on on site courses for larger groups

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Other Examples
This example comes from our "More on Character Strings" training module. You'll find a description of the topic and some other closely related examples on the "More on Character Strings" module index page.

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