my %modes; @modes{ qw < > >> +< +> +>>  } = ( 1, 2, 2, 128, 128, 128 );

how do I un-OR OR results, against the other flags, to get back to these basic constants?

(From MSVC header files:

#define _O_RDONLY       0x0000  /* open for reading only */
#define _O_WRONLY       0x0001  /* open for writing only */
#define _O_RDWR         0x0002  /* open for reading and writing */
#define _O_APPEND       0x0008  /* writes done at eof */
#define _O_CREAT        0x0100  /* create and open file */
#define _O_TRUNC        0x0200  /* open and truncate */
#define _O_EXCL         0x0400  /* open only if file doesn't already e
+xist */
#define _O_TEXT         0x4000  /* file mode is text (translated) */
#define _O_BINARY       0x8000  /* file mode is binary (untranslated) 
+*/
#define _O_WTEXT        0x10000 /* file mode is UTF16 (translated) */
#define _O_U16TEXT      0x20000 /* file mode is UTF16 no BOM (translat
+ed) */
#define _O_U8TEXT       0x40000 /* file mode is UTF8  no BOM (translat
+ed) */
[download]

So, assuming the variable $mode contains the OR'd values; you can check which bits are set something like:

if( $mode & 1 ) { ## _O_WRONLY
    say "File is opend WRITE only
}
[download]

But note: not all of the bits that can be set when opening a file are retained in FILE*->_flag.

---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Thumbs up for this load of code!! Thank you BrowserUk!

As I remember, I "discovered" them by writing a small C program that open files in each of the modes and then queried the numeric value using this code (from Fmode.xs):

int 
xs_fmode( FILE *stream ) {
    return stream->_flag;
}
[download]

And I discovered that incantation by finding the struct FILE definition in the C header files.

NOTE: This was done using MSVC header files; YMMV on other platforms.

---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

See also FileHandle::Fmode and Fcntl

#!/usr/bin/perl --
use strict; use warnings; use Data::Dump;
use Fcntl();
my %mode2symbol = (
#~     Fcntl::F_DUPFD()  => '&',
    Fcntl::O_RDONLY() => '<',
    Fcntl::O_RDWR()   => '+<',
    Fcntl::O_TRUNC()  => '>',
    Fcntl::O_WRONLY() => '>',
    Fcntl::O_APPEND() => '>>',
    Fcntl::O_CREAT()  => '>',
);

my %name2mode = (
#~     F_DUPFD  => Fcntl::F_DUPFD(),
    O_RDONLY => Fcntl::O_RDONLY(),
    O_RDWR   => Fcntl::O_RDWR(),
    O_TRUNC  => Fcntl::O_TRUNC(),
    O_WRONLY => Fcntl::O_WRONLY(),
    O_APPEND => Fcntl::O_APPEND(),
    O_CREAT  => Fcntl::O_CREAT(),
);

$mode2symbol{ $name2mode{O_RDWR} | $name2mode{O_APPEND} } = '+>>';
$mode2symbol{ $name2mode{O_RDONLY} | $name2mode{O_APPEND} } = '+>>';
$mode2symbol{ $name2mode{O_WRONLY} | $name2mode{O_APPEND} } = '+>>';

dd \%mode2symbol;
dd \%name2mode;
__END__
{
  "0"   => "<",
  "1"   => ">",
  "2"   => "+<",
  "8"   => "+>>",
  "9"   => "+>>",
  "10"  => "+>>",
  "256" => ">",
  "512" => ">",
}
{
  O_APPEND => 8,
  O_CREAT  => 256,
  O_RDONLY => 0,
  O_RDWR   => 2,
  O_TRUNC  => 512,
  O_WRONLY => 1,
}
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