Perl string functions - concatenate substring and split

Mar 31, 2013 by David Farrell

Perl has many string functions, let’s take a look at a some of the most common ones: concatenate, substring and split.

Concatenate

Concatenate strings by inserting a fullstop (.) operator between them. Perl will automatically ‘stringify’ scalar variables that were initialised as a number.

# declare and concatenate two strings
my $joke = 'A horse walks ' . 'into a bar.'; # A horse walks into a bar.
# Concatenate two scalars
my $meat  = 'ham';
my $bread = 'sandwich';
my $lunch = $meat . $bread; # hamsandwich

# Concatenate scalars initialised as numbers
my $hour        = 6;
my $minutes     = 30;
my $time_string = $hour . ':' . $minutes; # 6:30

Substring

Substring extracts and returns a sub-set of an existing string. It takes up to four arguments: the expression to substring, the offset from where to start the substring, the length of the substring and a replacement string. If the length is omitted the substring will run to the end of input expression.

# substr(expression, offset, [length], [replacement])
my $joke            = 'A horse walks into a bar.';
my $animal          = substr($joke, 2, 5); # horse
my $favourite_place = substr($joke, -4); # bar.

# Extract a substring and replace the substring in the original string
my $verb        = substr($joke, 8, 5, 'runs'); # walks
print $joke; # A horse runs into a bar.

The perldoc page for substr has many more useful examples.

Split

The split function divides an input string into a list of substrings using a split pattern, and an (optional) limit on the number of split fields. If the input expression is omitted, Perl will use $_.

# split(pattern, [expression], [number_of_fields])
my $sentence       = 'A horse walks into a bar.';
my @words          = split(' ', $sentence); # A,horse,walks,into,a,bar

my $fullname       = 'Mr Stephen Doyle';

# Limit the split to two fields
my @title_and_name = split(' ', $fullname, 2); # Mr,Stephen Doyle