Haven't tested it but this should work

Using a filehandle (as you were with <FILE>) only returns a line at a time.

my ($allsource) ;
while <FILE> {

    $allsource .= $_ ;

}

# Now $allsource contains all of the lines of the file

my (@segments) = split /%{5}/, $allsource ;

# Each element in @segments is one of the segments

# Could undefine $allsource to free a little memory
undef ($allsource) ;
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