johngg has asked for the wisdom of the Perl Monks concerning the following question:
When writing the script posted in this reply I originally tried to use unpack to extract each line after sorting but it mashed the output into a single line with no line feeds. (I went with substr instead). The documentation states that unpack does the reverse of pack but using the 'A' template seems to lose trailing newline characters when unpacking. Embedded newlines are preserved. Using the 'a' template instead works as expected.
use strict; use warnings; use feature qw{ say }; use List::Util qw{ max }; my $string = qq{abc\n}; my $packed = pack q{A*}, $string; my $unpacked = unpack q{A*}, $packed; say $string eq $packed ? q{OK - original and packed are the same} : q{Not OK - original and packed differ}; sideBySide( $string, $packed ); say $string eq $unpacked ? q{OK - original and unpacked are the same} : q{Not OK - original and unpacked differ}; sideBySide( $string, $unpacked ); say q{=} x 50; $string .= qq{def\n}; $packed = pack q{A*}, $string; $unpacked = unpack q{A*}, $packed; say $string eq $packed ? q{OK - original and packed are the same} : q{Not OK - original and packed differ}; sideBySide( $string, $packed ); say $string eq $unpacked ? q{OK - original and unpacked are the same} : q{Not OK - original and unpacked differ}; sideBySide( $string, $unpacked ); sub sideBySide { my( $original, $modified ) = @_; my @origChars = map { sprintf q{%#02x}, ord } split m{}, $original +; my @modChars = map { sprintf q{%#02x}, ord } split m{}, $modified +; my $nRows = max scalar( @origChars ), scalar( @modChars ); for ( 1 .. $nRows ) { printf qq{%8s%8s\n}, scalar @origChars ? shift @origChars : q{}, scalar @modChars ? shift @modChars : q{}; } }
The output.
OK - original and packed are the same 0x61 0x61 0x62 0x62 0x63 0x63 0xa 0xa Not OK - original and unpacked differ 0x61 0x61 0x62 0x62 0x63 0x63 0xa ================================================== OK - original and packed are the same 0x61 0x61 0x62 0x62 0x63 0x63 0xa 0xa 0x64 0x64 0x65 0x65 0x66 0x66 0xa 0xa Not OK - original and unpacked differ 0x61 0x61 0x62 0x62 0x63 0x63 0xa 0xa 0x64 0x64 0x65 0x65 0x66 0x66 0xa
My questions: is this a bugette, a feature, or am I having a senior moment?
Cheers,
JohnGG
|
---|
Replies are listed 'Best First'. | |
---|---|
Re: Problem with pack/unpack asymmetry
by Eily (Monsignor) on Jun 19, 2019 at 14:53 UTC | |
by johngg (Canon) on Jun 19, 2019 at 16:31 UTC | |
by shmem (Chancellor) on Jun 21, 2019 at 11:38 UTC | |
Re: Problem with pack/unpack asymmetry
by shmem (Chancellor) on Jun 19, 2019 at 14:49 UTC |
Back to
Seekers of Perl Wisdom