# File regex0.pl
# Regular expressions(regex). String =~ m/Pattern/  same as String =~ /Pattern/
# Match (m) the String with Pattern
# Last succesful match. System variables take values:
# 	$` =  first part 	(' quote)
#   $& = fit 
#	$' = last part     (` backquote)
#   position where match is found = length($`) -  # how many chars are before gives position
#	C:\myPerl>perl regex0.pl
#	Sequence=Blaise2012   Pattern=^Bla before=  fit=Bla    after=ise2012
#	Sequence=Blaise2012   Pattern=2012 before=Blaise  fit=2012    after=
#   Position in sequence =6
#	Sequence=Blaise2012  Pattern=[0-9] before=Blaise  fit=2  after=012 position=6
#	Sequence=Blaise2012  Pattern=b before=  fit=B  after=laise2012 position=0
#	Sequence=Blaise2012  Pattern=2..2 before=Blaise  fit=2012  after= position=6
#	Sequence=Blaise2012  Pattern=[0-9].2 before=Blaise2  fit=012  after= position=7
#	no match
$seq = 'Blaise2012';
# match with pattern starting(^) with Bla: before=(nothing) fit=Bla after=ise 2012
$seq =~ m/^Bla/;
print "\nSequence=$seq   Pattern=^Bla before=$`  fit=$&    after=$' " ;
# match with pattern: find anywhere 2012: before=Blaise  fit=2012 after= (nothing)
$seq =~ m/2012/;
print "\nSequence=$seq   Pattern=2012 before=$`  fit=$&    after=$' " ;
print "\nPosition in sequence =", length($`);  
# Match first digit. [0-9] means any digit. Finds first 2 position=6
$seq =~ m/[0-9]/;
print "\nSequence=$seq  Pattern=[0-9] before=$`  fit=$&  after=$' position=", length($`);
# find first B ignore case
$seq =~ m/b/ig;
print "\nSequence=$seq  Pattern=b before=$`  fit=$&  after=$' position=", length($`);
# look for a 4 length sequence that starts with 2 and ends with 2
$seq =~ m/2..2/;
print "\nSequence=$seq  Pattern=2..2 before=$`  fit=$&  after=$' position=", length($`);
# look for a 3 length sequence that starts with a digit and ends with 2
$seq =~ m/[0-9].2/;
print "\nSequence=$seq  Pattern=[0-9].2 before=$`  fit=$&  after=$' position=", length($`);
# find first HAPPY ignore case. No match!
# carefull! variables $`,$',$& detain the last values for succes!
# you have to always check before if match works when finding position.
if ($seq =~ m/HAPPY/) 
	{print "\n match";}
else 
	{print "\n no match";}
exit;