Perl: I/O examples

README

http://gist.github.com/2122

Examples of I/O in Perl.

pack.pl

#!/usr/bin/perl 
use strict; use warnings;

print STDERR "USAGE: <integer> on STDIN\nExample: 1008813135\n\n";

select STDOUT; $| = 1;  # immediately flush any output

my $in = <STDIN>;
print STDOUT pack("N", int($in)), "\n";

PackTest.java

import java.io.DataOutputStream;

public class PackTest {
    public static void main (String[] args) throws Exception {
        DataOutputStream out = new DataOutputStream(System.out);
        out.writeInt(11351);
        out.flush();
    }
}

stdio_redirect.pl

#!/usr/bin/perl 
use strict; use warnings;

open my $oldout, ">&", \*STDOUT     or die "Can't dup STDOUT: $!";
open OLDERR,     ">&", \*STDERR or die "Can't dup STDERR: $!";

#open STDERR, '>', "foo.out" or die "Can't redirect STDOUT: $!";
open STDOUT, ">&STDERR"     or die "Can't dup STDOUT: $!";

select STDERR; $| = 1;  # make unbuffered
select STDOUT; $| = 1;  # make unbuffered

print STDOUT "stdout 1\n";  # this works for
print STDERR "stderr 1\n";  # subprocesses too

print $oldout "stdout 2\n";  # this works for
print OLDERR "stderr 2\n";  # subprocesses too

open my $in, "<&", \*STDIN or die "Can't dup STDIN: $!";
open STDIN, "</dev/null" or die "Can't dup STDIN: $!";

my $i = <$in>;
print STDOUT $i;

$i = <STDIN>;
print STDOUT "STDIN gets nothing!\n" unless $i;

unpack.pl

#!/usr/bin/perl 
use strict; use warnings;

print STDERR "USAGE: <packed-integer> on STDIN\nExample: <!DO\n\n";

binmode STDIN, ':bytes';    # set to read bytes
read STDIN, my $bytes, 4;

print STDOUT unpack('N', $bytes), "\n";