1 while s/pattern/length($`)/e;

##</code><code>##

     1 while s/\t+/' ' x (length($&) * 8 - length($`) % 8)/e;

##</code><code>##

s/^([^ ]+) +([^ ]+)/$2 $1/;   # swap first two words
/(\w+)\s*=\s*\1/;             # match "foo = foo"
/.{80,}/;                     # match line of at least 80 chars
/^(\d+\.?\d*|\.\d+)$/;        # match valid number
if (/Time: (..):(..):(..)/) { # pull fields out of a line
        $hours   = $1;
        $minutes = $2;
        $seconds = $3;
}

##</code><code>##

$_ = <STDIN>;
s/.*(some_string).*/$1/;

##</code><code>##

s/.*(some_string).*/$1/s;
s/.*(some_string).*\n/$1/;
s/.*(some_string)[^\0]*/$1/;
s/.*(some_string)(.|\n)*/$1/;

chop; s/.*(some_string).*/$1/;
/(some_string)/ && ($_ = $1);

##</code><code>##

$pattern =~ s/(\W)/\\$1/g;

##</code><code>##

/$unquoted\Q$quoted\E$unquoted/

##</code><code>##

/^fee|fie|foe$/

##</code><code>##

/^(fee|fie|foe)$/