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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Finding all matches to a pattern in Perl regular expressions

A regular expression usually matches the leftmost occurrence of a pattern within an incoming (source) string.

This doesn't matter if all you're looking to do is find whether or not your source string contains something ... but if you're looking to make use of the part that matched, then it does make a difference. Consider
  $us = 'I am graham@wellho.net and you are pinkpanther@frenchdetectives.fr';
and the match
  /\S+\@\S+/

This will match graham@wellho.net every time you run it in Perl, and never pinkpanther@frenchdetectives.fr .

What if you want to match that second email address, then? You can add a modifier after the end of the regular expression - the single letter g which stands for "global".

* In a scalar content, but used in a loop, a global match carries on where the last match left off on each successive time around the loop, thus letting you loop though all valid, non-overlapping matches in the string. And when there are no more, a false result will be returned. Thus:

  while ($us =~ /\S+\@\S+/g) {
    print "Emma is $&\n";
    }


Will return each match it turn. By contrast, without the g this program would give you an infinite loop.

There are, as always, multiple ways of doing the same thing in Perl. If you use the g modifier in a list context (for example return the result of the match into a list), that list will be assigned to all non-overlapping matches. Thus:

  @gotted = $us =~ /\S+\@\S+/g;
  print "We got @gotted\n";


will output

  We got graham@wellho.net pinkpanther@frenchdetectives.fr

Complete program [here]. As taught during our Learning to program in Perl / Perl Programming training classes.

(written 2011-12-09, updated 2011-12-17)

 
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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