As I was just commenting in a different reply... The shell ties the prior program's (or user input to the first) output to the input of the next program. That

As I was just commenting in a different reply... The shell ties the prior program's (or user input to the first) output to the input of the next program. That's (old) stdout and (new) stdin taken care of. stderr is sent to the terminal as output by default. For reference stdin, stdout, and stderr are normally numbered 0 through 2 respectively. When you're directing input and output on the shell (usually) the default is to wire up things as they'd make sense, but (without any IFS characters) a number on either side of the redirection operator codes tells the shell to grab a different input or output. These will yield different results due to left to right parsing: echo test >/tmp/test 2>&1 echo test 2>&1 >/tmp/test In the second if there were any errors they'd be sent to the file, while in the first (assuming you can make temporary files, which normally you can) there won't be any errors printed but they would be sent as standard output on the shell. Here's a more interesting example echo test >/dev/null/test 2>/dev/null echo test 2>/dev/null >/dev/null/test The second line will silently fail (though it'll still return an exit value of 1) because the standard error output was already sent to /dev/null, while the first attempts to open a file that can't exist and prints the failure message before the error output is redirected.