Pipe

Not the same as a redirect

A redirect sends output to a file. A pipe sends it to another command — the difference between storing the result and continuing to work on it.

Where it bites

Only the left command’s normal output travels through the pipe; its errors go somewhere else and appear on your screen while the right-hand side receives nothing. An empty result from a pipeline usually means the first command failed, not that nothing matched.

In practice

$ cat log.txt | grep ERROR

Covered in these lessons

• Finding and fixing a bug
• The pipe: joining commands together

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