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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]
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 Books covering this topic
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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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