Engry Young Men - Perl

In addition to simple matching, Perl also allows you to perform substitutions.

Take a look at our next example, which prompts you to enter a line of text, and then replaces all occurrences of the letter "a" with the letter "e".

---

#!/usr/bin/perl
# get a line of input
print "Gimme a line!\n";
$line = ;
chomp ($line);
# substitute with the substitution operator
$line =~ s/a/e/;
# and print
print $line;

---

In this case, we've used Perl's substitution operator - it looks like this:

---

s/search-pattern/replacement-pattern/

---

In the example above, the line

---

$line =~ s/a/e/;

---

simply means "substitute a with e in the scalar variable $line".

And here's the output:

---

Gimme a line!
angry young man
engry young man

---

Ummm...didn't work quite as advertised, did it? All it did was replace the first occurrence of the letter "a". How about adding the "g" operator, which does a global search-and-replace?

---

#!/usr/bin/perl
# get a line of input
print "Gimme a line!\n";
$line = ;
chomp ($line);
# substitute with the substitution operator
$line =~ s/a/e/g;
# and print
print $line;

---

And this time,

---

angry young man

---

is replaced with

---

engry young men

---

Much better! But what if your sentence contains an upper-case "a", also known as "A". Well, that's why Perl also has the case-insensitivity operator "i", which takes care of that last niggling problem:

---

#!/usr/bin/perl
# get a line of input
print "Gimme a line!\n";
$line = ;
chomp ($line);
# substitute with the substitution operator
$line =~ s/a/e/gi;
# and print
print $line;

---

And the output:

---

Gimme a line!
Angry young man
Engry young men

---

Of course, we're just scratching the tip of the regex iceberg here. Things get even more interesting when you start using patterns and metacharacters instead of actual words...

This article copyright Melonfire 2000. All rights reserved.

>>> More Perl Programming Articles          >>> More By Vikram Vaswani and Harish Kamath, (c) Melonfire

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