deconstruction:

{
    # set $go and $/ to undef
    $go=$/=$go;

    # grab the data into $_
    $_=<DATA>;

    # ignore the "BAR" - this converts 'O' to '1' and 'F' to '0'
    y!FOO!01BAR!;

    # remove whitespace (so $_ just contains a big binary string)
    s! |\n!!go;
}
{
    # pack each 7 bit binary sequence into a character and
    # append to $go
    $go.=pack C,oct"0b$1" while s<(.{7})><>;
    
    # assign $_ the contents of $go
    $_=$go
}
{
    # this does nothing (but is funny)
    $go,$go,$go and 

    # sort character pairs then print the second char of each pair
    # seems familiar ;o)
    print map{m<.(.)>}sort m<..>go
}
 __DATA__

OOFFOOOOOFOO      OFOO       OOFFFOOOFFO    FOOO    FFOO    OFFO
FFFOOFOOOFOF    OFFFFOOF     OFFFOOFOOOOO   OFOO    FOFO    FFFF
    FOOO      FOOF    OOFO   FOOO    OFOF   OOOO    FFOF    OOOF
    OFOF      OOFO    FFFO   OFFF    OOOO   OFFO    OOOF    FFFO
    OFFO      FOFOOOFFOFFO   FFFFFOOOFOFF   OOFFFFOOOFFO    FFOO
    OFOF      FOOFFOFOFOFF   FFFOOFFOOFO    FFFFFOOOOFOF    OOOF
    FFOO      OOOF    FFOO   OFOO           FFOO    OFFF    FOOO
FF  OFOO      FOOO    OOOF   FOFO           OOFO    OFFO        
OOFFOFOO      FFFO    FOOO   FOFO           OOFO    FFOO    OOFO
 FFOOOF       OOOO    OFFO   FOOO           OOFF    OFOF    FFFO
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