How do I read the contents of a small text file into a scalar in Perl?

Question

I have a small text file that I'd like to read into a scalar variable exactly as it is in the file (preserving line separators and other whitespace).

The equivalent in Python would be something like

buffer = ""

try:
    file = open("fileName", 'rU')
    try:
        buffer += file.read()
    finally:
        file.close()
except IOError:
    buffer += "The file could not be opened."

This is for simply redisplaying the contents of the file on a web page, which is why my error message is going into my file buffer.

Answer 1

You could do something like:

$data_file="somefile.txt";
open(DAT, $data_file);
@file_data = <DAT>;
close(DAT);

That'll give you the file contents in an array, that you can use for whatever you want, for example, if you wanted each individual line, you could do something like:

foreach $LINE (@file_data)
{
    dosomethingwithline($LINE);
}

For a full usage example:

my $result;
$data_file = "somefile.txt";
my $opened = open(DAT, $data_file);
if (!$opened)
{
    $result = "Error.";
}
else
{
    @lines = <DAT>;
    foreach $LINE (@lines)
    {
        $result .= $LINE;
    }
    close(DAT);
}

Then you can use $result however you need. Note: This code is untested, but it should give you an idea.

Answer 2

As an alternative to what Alex said, you can install the File::Slurp module (cpan -i File::Slurp from the command line) and use this:

use File::Slurp;
# Read data into a variable
my $buffer = read_file("fileName");
# or read data into an array
my @buffer = read_file("fileName");

Note that this dies (well... croaks, but that's just the proper way to call die from a module) on errors, so you may need to run this in an eval block to catch any errors.

Answer 3

From the Perl Cookbook:

my $filename = 'file.txt';
open( FILE, '<', $filename ) or die 'Could not open file:  ' . $!;

undef $/;
my $whole_file = <FILE>;

I would localize the changes though:

my $whole_file = '';
{
    local $/;
    $whole_file = <FILE>;
}

Answer 4

There is a discussion of the various ways to read a file here.

Answer 5

Just join all lines together into a string:

open(F, $file) or die $!;
my $content = join("", <F>); 
close F;

(It was previously suggested to use join "\n" but that will add extra newlines. Each line already has a newline at its end when it's read.)

Answer 6

If I don't have Slurp or Perl6::Slurp near by then I normally go with....

open my $fh, '<', 'file.txt' or die $!;

my $whole_file = do { local $/; <$fh> };

/I3az/

Answer 7

I don't have enough reputation to comment, so I apologize for making this another post.

@ Harold Bamford: $/ should not be an obscure variable to a Perl programmer. A beginner may not know it, but he or she should learn it. The join method is a poor choice for the reasons stated in the article linked by hackingwords above. Here's the relevant quotation from the article:

That needlessly splits the input file into lines (join provides a list context to ) and then joins up those lines again. The original coder of this idiom obviously never read perlvar and learned how to use $/ to allow scalar slurping.

Answer 8

I'd tweak draegtun's answer like this, to make it do exactly what was being asked:

my $buffer;
if ( open my $fh, '<', 'fileName' ) {
    $buffer = do { local $/; <$fh> };
    close $fh;
} else {
    $buffer = 'The file could not be opened.';
}