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This is an excerpt from the latest version perlfaq5.pod, which
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5.28: How can I read in an entire file all at once?

You can use the File::Slurp module to do it in one step.

use File::Slurp;

$all_of_it = read_file($filename); # entire file in scalar
@all_lines = read_file($filename); # one line per element

The customary Perl approach for processing all the lines in a file is to
do so one line at a time:

open (INPUT, $file) || die "can't open $file: $!";
while (<INPUT>) {
# do something with $_
close(INPUT) || die "can't close $file: $!";

This is tremendously more efficient than reading the entire file into
memory as an array of lines and then processing it one element at a
time, which is often--if not almost always--the wrong approach. Whenever
you see someone do this:

@lines = <INPUT>;

you should think long and hard about why you need everything loaded at
once. It's just not a scalable solution. You might also find it more fun
to use the standard Tie::File module, or the DB_File module's $DB_RECNO
bindings, which allow you to tie an array to a file so that accessing an
element the array actually accesses the corresponding line in the file.

You can read the entire filehandle contents into a scalar.

local(*INPUT, $/);
open (INPUT, $file) || die "can't open $file: $!";
$var = <INPUT>;

That temporarily undefs your record separator, and will automatically
close the file at block exit. If the file is already open, just use

$var = do { local $/; <INPUT> };

For ordinary files you can also use the read function.

read( INPUT, $var, -s INPUT );

The third argument tests the byte size of the data on the INPUT
filehandle and reads that many bytes into the buffer $var.


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