How to create binary file in Perl?

Question

od -x test shows:

0000000 457f 464c 0102 0001

Now I want to use Perl to create such file.

open FH,'>','test_1';
#syswrite(FH,0x457f464c01020001); # not work
print FH 0x457f464c01020001;      # not work

How to create binary file in Perl?

For what it's worth, your code does "work", but it doesn't do what you want. It converts the hex representation to its internal number format (probably losing a bunch of bits in the conversion), then prints the decimal representation of the number. Think about it - you would hardly want print 1; to print a ctrl-A. — tripleee
– tripleee, Commented Feb 29, 2012 at 6:51

ikegami · Accepted Answer · 2012-02-29 22:30:25Z

7

To create a binary file, one uses

open (my $fh, '>:raw', $qfn)

To place

45 7f 46 4c 01 02 00 01

in that file, one can use any of the following:

# Starting with a string of those bytes.
print $fh "\x45\x7f\x46\x4c\x01\x02\x00\x01";

# Starting with a hex representation of the file.
print $fh pack('H*', '457f464c01020001');

# Starting with the bytes.
print $fh map chr, 0x45, 0x7f, 0x46, 0x4c, 0x01, 0x02, 0x00, 0x01;

# Starting with the bytes.
print $fh pack('C*', 0x45, 0x7f, 0x46, 0x4c, 0x01, 0x02, 0x00, 0x01);

edited Feb 29, 2012 at 22:30

answered Feb 29, 2012 at 7:03

ikegami

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Vikram · Accepted Answer · 2012-02-29 06:19:07Z

2

open(my $out, '>:raw', 'test_1.bin') or die "Unable to open: $!";
print $out pack('s<',255) ;
close($out);

also you can look at the perl pack functions here

answered Feb 29, 2012 at 6:19

Vikram

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1 Comment

Paul Over a year ago

Alternative to set file to binary mode: binmode(FH); It's worth understanding what 's' represents (for OP): perldoc.perl.org/functions/pack.html

William Pursell · Accepted Answer · 2012-02-29 06:24:51Z

1

print FH pack 'H*', '457f464c01020001'

answered Feb 29, 2012 at 6:24

William Pursell

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hobbs · Accepted Answer · 2012-02-29 06:31:31Z

0

print FH "\x45\x7f\x46\x4c\x01\x02\x00\x01" is another way. See Quote and Quote-like Operators in perlop for more information about escape sequences available in strings. \x works like it does in C... except that Perl has an extended syntax that goes beyond \xff.

answered Feb 29, 2012 at 6:31

hobbs

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