An octal number is preceded by a 0 and contains digits from 0 to 7 only. By calling the oct function, there are two particular cases here – the expression will be interpreted as a hexadecimal string if begins wit 0x and as a binary string if it begins with 0b. If you want to convert numbers in or from a binary, octal or hexadecimal format you need to write them as literals, otherwise no automatic conversion will take place. The leading white spaces from the expression string will be omitted.

The syntax of the Perl oct function looks like this:

oct EXPR
oct

If the expression is omitted, the $_ is used instead.

Please notice that the Perl oct function can convert a binary, octal or hexadecimal number into a decimal format, whereas the hex function converts only hexadecimal numbers, with or without the prepended 0x.

#!/usr/local/bin/perl

use strict;
use warnings;

print oct(77), "\n";        # it prints 63

print oct('77'), "\n";      # it prints 63

print oct('077'), "\n";     # it prints 63

print oct(077), "\n";       # it prints 51
# because 077 is an octal number, first it will
# be converted to a decimal number, i.e. 63 and next
# oct(63) means 51

print oct('2382'), "\n";    # it prints 19
# this statement will throw a warning error
# because 8 is not a digit in the octal base; however, 
# the rest of digits starting with 8 will be ignored and the oct
# function will convert the octal number 23 in decimal 

print oct('0x77'), "\n";    # it prints 119
# '   0x77' is considered the hexadecimal number 77; 
# converted in decimal this means 119; 
# the leading spaces are ignored

print oct('0b101'), "\n";   # it prints 5
# '0b101' is considered the binary number 101; 
# converted in decimal this means 5

For example, if you want to assign the 644 permission to a file (which means that owner can read and write and other people only read) you can use any of the two following lines of code:

chmod(0664, $file);
chmod(oct(664), $file);

In the following, I remind you how to use the octal syntax notation in connection with the file permission.

The first digit of the octal number 664 is for the owner, the second for the group and the last for others. The permission could be r (for reading), w (for writing), x (for executing) and – (no permission).

Each digit of the permission number can have one of the following values:

So 664 means the following permissions:

rw-rw-r-- (the owner and the group can read and write, the other people only read)

Please click here to download the Perl oct script with all the above examples included.