Global matching
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Regexp='ba[rz]', Opts='g'
  last string='foobarbaz'
  number of matches = 1
  0 - bar
Regexp='ba[rz]', Opts='g'
  last string='foobarbaz'
  number of matches = 1
  0 - baz

Global matching with back-refs
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Regexp='(ba[rz])', Opts='g'
  last string='foobarbaz'
  number of matches = 2
  0 - bar
  1 - bar
Regexp='(ba[rz])', Opts='g'
  last string='foobarbaz'
  number of matches = 2
  0 - baz
  1 - baz

Matching with nested back-refs
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Regexp='([\w\.-]+)@((\d+)\.(\d+)\.(\d+)\.(\d+))', Opts=''
  last string='matevz.tadel@137.138.170.210'
  number of matches = 7
  0 - matevz.tadel@137.138.170.210
  1 - matevz.tadel
  2 - 137.138.170.210
  3 - 137
  4 - 138
  5 - 170
  6 - 210

Split
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Regexp=':', Opts=''
  last string='root:x:0:0:root:/root:/bin/bash'
  number of matches = 7
  0 - root
  1 - x
  2 - 0
  3 - 0
  4 - root
  5 - /root
  6 - /bin/bash

Split with maxfields=5
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Regexp=':', Opts=''
  last string='root:x:0:0:root:/root:/bin/bash'
  number of matches = 5
  0 - root
  1 - x
  2 - 0
  3 - 0
  4 - root:/root:/bin/bash

Split with empty elements in the middle and at the end
maxfields=0, so trailing empty elements are dropped
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Regexp=':', Opts=''
  last string='root::0:0:root:/root::'
  number of matches = 6
  0 - root
  1 - 
  2 - 0
  3 - 0
  4 - root
  5 - /root

Split with empty elements at the beginning and end
maxfields=-1, so trailing empty elements are kept
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Regexp=':', Opts=''
  last string=':x:0:0:root::'
  number of matches = 7
  0 - 
  1 - x
  2 - 0
  3 - 0
  4 - root
  5 - 
  6 - 

Split with no pattern in string
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Regexp=':', Opts=''
  last string='A dummy line of text.'
  number of matches = 1
  0 - A dummy line of text.

Split with regexp potentially matching a null string 
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Regexp=' *', Opts=''
  last string='hi there'
  number of matches = 7
  0 - h
  1 - i
  2 - t
  3 - h
  4 - e
  5 - r
  6 - e

Split on patteren with back-refs
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Regexp='([,-])', Opts=''
  last string='1-10,20'
  number of matches = 5
  0 - 1
  1 - -
  2 - 10
  3 - ,
  4 - 20

Substitute
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Regexp='(\d+)\.(\d+)\.(\d+)\.(\d+)', Opts=''
Substitute '137.138.170.210','$4.$3.$2.$1' => '210.170.138.137'

Global substitute
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Regexp='(\w+)\.(\w+)@[\w\.-]+', Opts='g'
Substitute 'rene.brun@cern.ch, philippe.canal@fnal.gov, fons.rademakers@cern.ch','\u$1 \U$2\E' => 'Rene BRUN, Philippe CANAL, Fons RADEMAKERS'