Perl read file
last modified August 24, 2023
In this article we show how to read files in Perl.
To read files in Perl, we can use built-in open, read
functions or utilize external modules such as Path::Tiny or
IO::All.
sky water rock falcon cloud war nice cup wrong forest blue bottle pen chair cup
We use a simple text file.
Perl read text file I
In the first example, we read the contents of the text file with
open and a for loop.
#!/usr/bin/perl
use v5.34.0;
use warnings;
open my $fh, "<", "words.txt"
or die "cannot open file $!";
print $_ for <$fh>;
close $fh;
We read the contents of the file line by line.
open my $fh, "<", "words.txt"
or die "cannot open file $!";
With open function, we open a file handle in read-only mode to the
specified text file.
print $_ for <$fh>;
We go over the file handle with the for loop and print the contents
of the file line by line.
close $fh;
In the end, we close the handle with close.
$ ./main.pl sky water rock falcon cloud war nice cup wrong forest blue bottle pen chair
Perl read text file II
The second example uses a while loop to read a text file.
#!/usr/bin/perl
use v5.34.0;
use warnings;
open my $fh, "<", "words.txt"
or die "cannot open file $!";
while (<$fh>) {
print $_;
}
close $fh;
Using the while loop and the <> operator, we read the file
line by line.
Perl diamond operator
Perl allows to read a file without explicitly opening it.
#!/usr/bin/perl
use v5.34.0;
use warnings;
while (<>) {
print $_;
}
The diamond operator (<>) will look at the @ARGV
for files to open and process.
$ ./main.pl words.txt sky water rock falcon cloud war nice cup wrong forest blue bottle pen chair cup
We pass the file name as a parameter to the Perl program.
Perl slurp text file
For relatively small files, we can read the whole file into a variable in one step.
#!/usr/bin/perl
use v5.34.0;
use warnings;
use Path::Tiny;
my $f = path('./words.txt');
my $res = $f->slurp;
print($res);
In the example, we use the Path::Tiny module.
my $f = path('./words.txt');
We create a path object.
my $res = $f->slurp;
We read the contents into a variable with slurp.
Perl read text file into array
In the next example, we read the text file into an array.
#!/usr/bin/perl
use v5.34.0;
use warnings;
use Path::Tiny;
my $f = path('./words.txt');
my @lines = $f->lines;
print $_ for (@lines);
In the program, we use Path::Tiny and its lines member
function.
Perl head/tail example
In the next example, we create a head/tail utility.
#!/usr/bin/perl
use v5.34.0;
use warnings;
use Path::Tiny;
my $f = path('./words.txt');
my $n = shift || 5;
my @lines = $f->lines( { count => $n } );
print $_ for (@lines);
The program reads n lines from the top or bottom of the text file.
my $n = shift || 5;
We provide the number of lines to read on the command line. If we do not give any value, five lines are read from the top.
my @lines = $f->lines( { count => $n } );
The number of lines to read is given to the count option. It also
accepts negative integers.
$ ./main.pl 3 sky water rock $ ./main.pl sky water rock falcon cloud $ ./main.pl -2 chair cup
Perl read web page
In the next example, we read a remote file (a web page resource).
#!/usr/bin/perl
use v5.34.0;
use warnings;
use HTTP::Tiny;
my $url = 'http://webcode.me/small.txt';
my $r = HTTP::Tiny->new->get($url);
if ($r->{success}) {
my $content = $r->{content};
print($content);
}
To read the resource, we use the HTTP::Tiny module.
$ ./main.pl small text page
Perl read binary file
The following example reads a binary file and prints the contents in hexadecimal.
#!/usr/bin/perl
use v5.34.0;
use warnings;
open my $fh, "<:raw", "favicon.ico"
or die "cannot open file $!";
my $block_size = 1024;
my $data;
my $n = 1;
while ( read $fh, $data, $block_size ) {
my @res = split( //, $data );
foreach (@res) {
printf( "%02x ", ord($_) );
$n++;
if ( $n > 20 ) {
print("\n");
$n = 1;
}
}
}
print "\n";
close $fh;
The program reads a small icon. We utilize the open,
read, and split functions.
open my $fh, "<:raw", "favicon.ico"
or die "cannot open file $!";
We open the file for reading in raw mode.
while ( read $fh, $data, $block_size ) {
In a while loop, we read the data into the buffer by 1024 byte chunks.
my @res = split( //, $data );
foreach (@res) {
printf( "%02x ", ord($_) );
$n++;
if ( $n > 20 ) {
print("\n");
$n = 1;
}
}
We split the raw line into bytes and print them in hexadecimal format. There are 20 bytes per line.
$ ./main.pl 00 00 01 00 01 00 10 10 00 00 00 00 00 00 68 05 00 00 16 00 00 00 28 00 00 00 10 00 00 00 20 00 00 00 01 00 08 00 00 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 ff ff ff 00 4d 45 3d 00 00 00 00 00 00 00 ...
In this article we have read text and binary files in Perl.
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