Perl Substitution Operators

(Updated: )
IT

Searching and Replacing

Operator Syntax Description
Match Operator /PATTERN/ Match the given pattern
Match Operator m/PATTERN/ Match the given pattern
Search & Replace s/PATTERN/REPLACE/ Search and replace the pattern
Char. S&R tr/searchlist/replacelist/ Character search and replace
Split split(/PATTERN/, $line) Split on regex pattern

The Substitution Operator (s///)

  • The substitution operator (s///) is used to change strings

IMPORTANT* : **looks like the original text is replaced, and actually the $result simply stores the NUMBER of substitutions made, not the actual result. **

1
2
3
4
5
6
7
8
9
10
$needToReplace = "bbb";
$replacementText = "1234567890";

$_ = "AAA bbb AAA";

$result = s/$needToReplace/$replacementText/; 

print $_; print "\n";

print $result; # notice how this is '1'. why? 
1
2
AAA 1234567890 AAA
1

Options for Substitution Operator

Option Description
e Forces Perl to evaluate the replacement pattern as an expression
g Replaces all occurrences of the pattern in the string
i Ignores the case of characters in a string
m Treats string as multiple lines (any \n will be the end of a single match)
s Treats string as a single line (treats \n as any other character)
o Compiles pattern only once
x Allows for extended regular expressions (ignores white spaces within the / /) 
1
2
3
4
$_ = "home, sweet home!"; 
s/home/cave/g; #no target results to default target

print "$_\n"; # output: cave, sweet cave!
1
cave, sweet cave!

removing excessive whitespaces

1
2
3
4
5
6
7
8
9
10
11
12
$_ = "   Input    data\t may have      extra whitespace. "; 
print "$_\n";

s/\s+/ /g;

# replaces all white space with a single whitespace
print "$_\n"; # output: " Input data may have extra whitespace."

# remove the whitespace in the beginning
s/^\s+//; # replaces 1 or more leading whitespaces with nothing 

print "$_\n";
1
2
3
   Input    data         may have      extra whitespace. 
 Input data may have extra whitespace.
Input data may have extra whitespace.