Modifiers

 

e	Evaluate the replacement side as an expression
i	Turn off case sensitivity
m	Treat a string as multuple lines. Let ^ and $ match next to embedded \n
o	Compile pattern only once. Used to optimize the search
s	Treat string as single line when newline is embedded. Let . match newline
x	Allows whitespace and comments whithin the regex
g	Replace globally, i.e. find all occurrences
gc	Alows continued search after failed /g match

 

-  e  -
1.	1 while $line =~ s/\t/' ' x (8 - $-[0] % 8)/e;
2.	$var=121; $var =~ s/2/2*4/e;	# 181
3.	$var=121; $c=4; $var =~ s/2/" $c*2 "/e;	# 1 4*2 3
4.	$var=121; $c=4; $var =~ s/2/" $c*2 "/ee;	# 181

 

-  i  -
	$word="AbCdeF";
1.	print "$word\n" if $word =~ /abcd|ABCD/;	#
2.	print "$word\n" if $word =~ /abcd|ABCD/i;	# AbCdeF

 

-  m  -
1.	$str= "1. Smith\n\tJey \n\tAn\n2. Shevchenko\n\tTaras \n";
	while ( $str =~ /(^\d.*$)/gm {
	print "$1\n";	# 1. Smith
	}	# 2. Shevchenko

 

-  x  -
	$a = "ABC"; $b = "WWW"; $c = "--($a)--($b)--";
1.	$c =~ s/
	\( # left parenthese
	(\w+) # capture any word
	\) # right parenthese
	/ $1 /xg;	# -- ABC -- WWW --

 

-  s  -
	$str = "12\n34";
1.	$str =~ s/./+/g;	# ++
		# ++
2.	$str =~ s/./+/sg;	# +++++

 

-  g  -
	$name = "anatoliy";
1.	$name = s/(\w)/uc($1)/e;	# Anatoliy
2.	$name = s/(\w)/uc($1)/eg;	# ANATOLIY

 

-  gc  -
	$_ = "123456abc7x"; $num = "\d\d\d"; $let = qr/[a-zA-Z]{3}/;
1.	while (1) {
	if (m/($num)/g) { print "NUM: $1\n"; }
	elsif (m/($let)/g) { print "LET: $1\n"; }
	else { print "pos = " . pos() "\n" and last; }
	}
	# infinitive loop
2.	while (1) {
	if (m/\G($num)/g) { print "NUM: $1\n"; }
	elsif (m/\G($let)/g) { print "LET: $1\n"; }
	else { print "pos = " . pos() "\n" and last; }
	}
	# NUM: 123
	# NUM: 456
	# Use of uninitialized value in concatenation ...
	# pos =
3.	while (1) {
	if (m/\G($num)/gc) { print "NUM: $1\n"; }
	elsif (m/\G($let)/gc) { print "LET: $1\n"; }
	else { print "pos = " . pos() "\n" and last; }
	}
	# NUM: 123
	# NUM: 456
	# LET: abc
	# pos = 9