EXPRESSION EFFECT
open (FH, "open (FH, "+open (FH, ">filename") Opens file name for writing.
open (FH, "+>filename") Opens file name for both reading and writing.
open (FH, ">>filename") Opens file name for appending.
open (FH, "command|") Runs the command and pipes its output to the filehandle.
open (FH, "|command") Pipes the output along the filehandle to the command.
open (FH, "-") Opens STDIN.
open (FH, ">-") Opens STDOUT.
open (FH, "<&=N") Where N is a number, this performs the equivalent of C's fdopen for reading.
open (FH, ">&=N") Where N is a number, this performs the equivalent of C's fdopen for writing.