Practice 3. Regular Expressions: Matching and Substitution(Transformation)

A. Patern Matching : Operator "=~/ /"
A-1) Standard form
$result = "I love cat and dog." =~/dog/ ;
if ($result)
{ print "Match ! \n";
} else {
print "No Match ! \n";
}

A-2) Practical form: using "$_"
$_ = "I love cat and dog." ;
if (/dog/)
{ print "Match ! \n";
} else {
print "No Match ! \n";
}

A-3) Matching Rules
=~/dog/ : standard
=~/d.g/ : arb. one letter for "o"
=~/d?g/ : 0 or 1 time repreat of "d"
=~/d*g/ : 0 or more of "d" (ex: dg, dddg,..)
=~/d+g/ : 1 or more of "d"
... (See the reference table.)



---


B. Substitution: Operator "=~s/ / /"
B-1) Standard form
$str = "I like dog." ;
$result = $str =~ s/dog/cat/ ;

B-2) Practical form: using "$_"
$_ = "I like dog." ;
$result = s/dog/cat/ ; <--"$_=~" can be omitted.

B-3) Substition vs. Transformation: "=~tr/ / /"
$_ = "I like dog." ;
$result = tr/abcd/ABCD/ ; <--Exchanging ONE BY ONE.