Connect commands

This is where the command line is at its strongest. Join small tools together and build whatever you need on the spot.

The idea to hold on to is ways out and ways in. Every command has two ways out (the ordinary result, called standard output, and the errors, called standard error) and one way in (standard input).

• > — point the way out at a file (overwriting)
• >> — add to the end of a file
• 2> — split the errors off on their own
• < — pour a file into the way in
• | — wire the way out of one command to the way in of the next
• tee — show it on the screen and keep it in a file at the same time
• xargs — turn the text flowing past into arguments for the next command

> overwrites in silence. Point it at a file with something in it and the original contents are gone. This chapter has you do that once on purpose, so get the habit into your fingers.

By the time you get here, work you used to do by tapping away at a screen fits on one line.