Stderr Redirection: 2>, 2>&1, &>

The stream that doesn't pipe by default

Pipes only carry stdout. Errors go to your screen no matter how many | stages follow. To capture, hide, or pipe errors you have to redirect stderr explicitly.

The three patterns you'll use forever

cmd 2> err.log — send stderr to a file.
cmd 2>/dev/null — silence stderr.
cmd 2>&1 — merge stderr into stdout.

Combine them: cmd 2>&1 | grep ERROR finds errors across both streams. cmd > out.log 2>&1 captures everything into one file.

Order matters

Redirection is processed left-to-right and each &1 means "wherever fd 1 currently points." Compare:

cmd > out.log 2>&1 → stdout to file, then stderr to wherever stdout is now (= the file). Both end up in out.log.
cmd 2>&1 > out.log → stderr to wherever stdout is (= terminal), then stdout to file. Errors stay on screen!

Bash 4+ shortcut: &>

cmd &> out.log redirects both streams. cmd &>> out.log appends. Cleaner than > out.log 2>&1 when you don't need to keep them separate. Doesn't work in POSIX sh, so for portable scripts use the long form.

# Find without permission spam find / -name 'todo.md' 2>/dev/null # Capture everything in one log ./long_build.sh > build.log 2>&1 # See errors only on screen, save stdout to file ./long_build.sh > build.log # Send only errors to a file ./long_build.sh 2> errors.log

Stderr Redirection: 2>, 2>&1, &>

The stream that doesn't pipe by default

The three patterns you'll use forever

Order matters

Bash 4+ shortcut: &>

Code

External links

Exercise

Progress

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