If you match a string to a regular expression, there are often lots of ways it can match. And if you're just saying "does this match", that's fair enough ... but if you're wanting to extract the matched data, you need to give it more thought.
A Perl match to
/-?\d+\.\d+/ in an
if statement will give the leftmost match, and the longest match from that point - so if the data is
123454_AM_by -0.48486638 1.2125003 0.20711732
you'll match -0.48486638 (and not -0.4 and not 1.2125003 ...). You can access the matched string via
$& (there are other prettier ways) if you want.
By adding a
g for global on the match, and performing the match in a
while loop, you can loop through all
non-overlapping matches:
while ($info =~ /\s-?\d+\.\d+/g) {
print "Matched in loop to $&\n";
}
giving
Matched in loop to -0.48486638
Matched in loop to 1.2125003
Matched in loop to 0.20711732
and you
could then push each matched element onto a list for later processing.
However, if you want a list of matches, there are often better ways using
split (where you specify a regular expression for the separators you
don't want) and the possibly
grep to filter our required elements:
@m2 = grep(/^-?\d+\.\d+$/,split(/\s+/,$info));
print "Matching fields: @m2\n";
Full source code example
[here], and subject covered on our
Learning to program in Perl and
Perl Programming course. More advanced delegates might like to take a look at our
Perl for larger projects course.
(written 2012-11-19, updated 2012-11-24)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
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)
[597] Storing a regular expression in a perl variable - (2006-02-09)
[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)
[1947] Perl substitute - the e modifier - (2008-12-16)
[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)
[3707] Converting codons via Amino Acids to Proteins in Perl - (2012-04-25)
[4452] Binary data handling - Python and Perl - (2015-03-09)
Some other Articles
Optional positional and named parameters in PythonReporting the full stack trace when you catch a Python exceptionMelksham Bus Issues - to be raised at First Bus Customer PanelStoring your intermediate data - what format should you you choose?First match or all matches? Perl Regular ExpressionsFiltering PHP form inputs - three ways, but which should you use?Red sky at nightThe bedrooms at Well House Manor35 minutes is only a slight delay on our railway serviceTwerp - A person regarded as insignificant and contemptible