my $file_handle = open(file.txt)
my $text;
while (read $file_handle, $buff, 1024) { $text = $buff }
read returns the number of characters read (0 when it's finished which will end the loop). I don't know of any generic "read" function, so it's up to you to define how many characters at a time and give the $buffer scalar to read into. it's just a different way of doing things
norkakn is a better resource than this comment
my $text = do { local( @ARGV, $/ ) = $file ; <> } ;
For the record, the do() block defines @ARGV (which normally holds the command-line arguments) to contain the value of the $file (presumably a file name), and sets $/ (which is the input record separator) to an undefined value. In Perl, <> is synonymous to <STDIN> which makes it read from stdin. Since @ARGV now contains a file name, Perl will open this file for reading. Since $/ is undefined, Perl will enter in "slurp" mode, and will gobble up the whole file in one shot. Since this is the last statement in the do() block, it will be returned as its value, and stored in $text.
Lots of Perl magic happening here. I advise you against using such shortcuts.
or
my $txt = do { local $/; <$file>; };
are as I know the preferred ways to do it. As a previous comment explained, $/ is the record separator and when you localize it it's value is set to undef. Which means we read the whole filehandle (the second part). As a do block evaluates to the value of the last expression, the contents of the file is the result of the whole expression.
If you're serious about Perl I recommend Modern Perl which is a 250 page really good introduction for the language, intended for programmers.
open( my $fh, '<', $file ) or die "cannot open $file\n";
my $text = do { local( $/ ) ; <$fh> } ;
http://perldoc.perl.org/perlopentut.html
http://perldoc.perl.org/functions/do.html
http://perldoc.perl.org/functions/local.html
http://perldoc.perl.org/perlop.html#I%2fO-Operators