I Lied: Redirection

Shell - OS X, Windows, Linux

I lied. Twice. Well, probably more than that, but specifically about input and output.

These are really instances of input or output redirection.

We already covered that < is input redirection (I previously called this piping in from a file).

We also covered output redirection:

• > - redirect output to a file
• >> - redirect output and append to a file
• 2> - redirect standard error to a file

Sometimes I’d like both STDOUT and STDERR to end up in the same file… check this out!

grep * > outfile 2>&1

The > outfile portion is just like from before. The 2>&1 portion says take STDERR (2) and point it at STDOUT (1).

Redirecting to a black hole:

Redirect to /dev/null to send output into a black hole.

I use this when I’m running a program with lots of output that I don’t care about (outputting to the screen is slow!). Redirect it to /dev/null and it will be much faster.