# File regex2.pl
# Regular expressions(regex). String =~ /Pattern/  same as String =~ m/Pattern/
# Match (m) the String with Pattern
# Last succesful match. System variables take values:
# 	$` =  first part  $& = fit    $' = last part    
#   position where match is found length($`) -how many chars are before gives position
#	C:\myPerl>perl regex2.pl
#	Charles   Darwin wrote XXX in 1859.
#	Input regular expression (type ENTER for quit)?.
#	Pattern=.
#	before=  fit=C  after=harles   Darwin wrote XXX in 1859. position=0
#	Charles   Darwin wrote XXX in 1859.
#   Input regular expression (type ENTER for quit)?\.
#   Pattern=\.
#   before=Charles   Darwin wrote XXX in 1859  fit=.  after= position=34
#   Charles   Darwin wrote XXX in 1859.
#   Input regular expression (type ENTER for quit)?\s\s
#   Pattern=\s\s
#   before=Charles  fit=    after= Darwin wrote XXX in 1859. position=7
#   Charles   Darwin wrote XXX in 1859.
#   Input regular expression (type ENTER for quit)?[1-9]
#   Pattern=[1-9]
#   before=Charles   Darwin wrote XXX in   fit=1  after=859. position=30
#   Charles   Darwin wrote XXX in 1859.
#   Input regular expression (type ENTER for quit)?Dar
#   Pattern=Dar
#   before=Charles     fit=Dar  after=win wrote XXX in 1859. position=10
#   Charles   Darwin wrote XXX in 1859.
#   Input regular expression (type ENTER for quit)?q
#   Bye
######################
$regex = ''; 
while( true )  { 	# while regex is not q (quit)
	$seq = 'Charles   Darwin wrote XXX in 1859.';  #there are 3 spaces between Charles and Darwin
	print "\n$seq \nInput regular expression (type ENTER for quit)?";
	$regex = <STDIN>; 	chop($regex);
	if ($regex eq 'q' or $regex eq 'Q') { last}; # q means quit last=break
	if ( $seq =~ m/$regex/ ) 
		{
		print "\nPattern=$regex \n before=$`  fit=$&  after=$' position=", length($`);
		}
	else
		{
		print "\n No match! $regex in $seq" ;
		}
}
print "Bye";
exit;