$mode = sprintf "%o", 420; # $mode = 644
chmod $mode, $file;

##</code><code>##

chmod 01204, $file; # 01204 octal == 644 decimal

##</code><code>##

# 1. octal number
chmod 0644, $file;
# 2. decimal number
chmod 420, $file;
# 3. number in a scalar
$mode = 0644;
chmod $mode, $file;
# 4. number in a scalar (from decimal)
$mode = 420;
chmod $mode, $file;
# 5. number with bitmasks
$mode = 0666 & ~022; # like umask
chmod $mode, $file;
# 6. decimal with bitmasks
$mode = 438 & ~022; # 438 == 0666
chmod $mode, $file;