When you match to a regular expression in a perl program, the program has to compile the regular expression (i.e. work out what it does) before actually doing the matching. It's pretty smart about that - it stored the result of than compile so that it only has to do it once during each run. However, if the regular expression contains a variable, Perl is slowed right down as the variable could change and Perl has to recompile every time.
If the variable isn't, in fact, going to change very often during a run you can control the compiling yourself by using a scalar variable to store the compiled regular expression using
qr, as shown in this example:
$local = "TR|PL|EX|TQ|TA|SN|BA|BS|DT|BH|GL";
$pcode = qr/^\s*($local)\d\w?\s+\d[A-Z]{2}\s*$/;
@vcheck = ("SN12 6QL","G3 7XR","GLZ 7PX"," OX11 0EY","NW1 1AD");
foreach $tp (@vcheck) {
$tp =~ $pcode and print "$1\n";
}
This gave me the single result "SN" as being the only valid postcode within the areas listed in $local.
(written 2006-02-09, updated 2006-06-05)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P669 - Perl - Data Munging [1316] Filtering and altering Perl lists with grep and map - (2007-08-23)
[1509] Extracting information from a file of records - (2008-01-16)
[1947] Perl substitute - the e modifier - (2008-12-16)
[2129] Nothing beats Perl to solve a data manipulation requirement quickly - (2009-04-14)
[2702] First and last match with Regular Expressions - (2010-04-02)
[3335] Practical Extraction and Reporting - (2011-06-26)
[3707] Converting codons via Amino Acids to Proteins in Perl - (2012-04-25)
[3764] Shell, Awk, Perl of Python? - (2012-06-14)
[4620] Perl 6 - a Practical Extraction and Reporting example! - (2016-01-11)
P212 - Perl - More on Character Strings [453] Commenting Perl regular expressions - (2005-09-30)
[583] Remember to process blank lines - (2006-01-31)
[586] Perl Regular Expressions - finding the position and length of the match - (2006-02-02)
[608] Don't expose your regular expressions - (2006-02-15)
[737] Coloured text in a terminal from Perl - (2006-05-29)
[928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
[943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
[1222] Perl, the substitute operator s - (2007-06-08)
[1230] Commenting a Perl Regular Expression - (2007-06-12)
[1251] Substitute operator / modifiers in Perl - (2007-06-28)
[1305] Regular expressions made easy - building from components - (2007-08-16)
[1336] Ignore case in Regular Expression - (2007-09-08)
[1510] Handling Binary data (.gif file example) in Perl - (2008-01-17)
[1727] Equality and looks like tests - Perl - (2008-07-29)
[1735] Finding words and work boundaries (MySQL, Perl, PHP) - (2008-08-03)
[2230] Running a piece of code is like drinking a pint of beer - (2009-06-11)
[2379] Making variables persistant, pretending a database is a variable and other Perl tricks - (2009-08-27)
[2657] Want to do a big batch edit? Nothing beats Perl! - (2010-03-01)
[2801] Binary data handling with unpack in Perl - (2010-06-10)
[2834] Teaching examples in Perl - third and final part - (2010-06-27)
[2874] Unpacking a Perl string into a list - (2010-07-16)
[2877] Further more advanced Perl examples - (2010-07-19)
[2993] Arrays v Lists - what is the difference, why use one or the other - (2010-10-10)
[3059] Object Orientation in an hour and other Perl Lectures - (2010-11-18)
[3100] Looking ahead and behind in Regular Expressions - double matching - (2010-12-23)
[3322] How much has Perl (and other languages) changed? - (2011-06-10)
[3332] DNA to Amino Acid - a sample Perl script - (2011-06-24)
[3411] Single and double quotes strings in Perl - what is the difference? - (2011-08-30)
[3546] The difference between dot (a.k.a. full stop, period) and comma in Perl - (2011-12-09)
[3630] Serialsing and unserialising data for storage and transfer in Perl - (2012-02-28)
[3650] Possessive Regular Expression Matching - Perl, Objective C and some other languages - (2012-03-12)
[3927] First match or all matches? Perl Regular Expressions - (2012-11-19)
[4452] Binary data handling - Python and Perl - (2015-03-09)
Some other Articles
A fond memory of Sir FreddieIt costs nothing to say THANK YOUPerl/Tk real time displayShould we cruise around the world?Storing a regular expression in a perl variableThe magic of -textvariableAdd a friendly front end with TkTwice is a co-incidence and three times is a patternFinding where the disc space has goneNOT Gone phishing