bash redirect stderr to stdout — 2>&1 and &>

Q: Pipe both output streams into another command

A pipe normally forwards stdout only. Put 2>&1 on the command before the pipe when stderr should be processed too. ``` # Send stdout and stderr to grep command 2>&1 | grep -i "error" # Keep the pipeline status meaningful when an earlier command fails set -o pipefail ```

Quick Answer

# Redirect stderr to stdout (combine both streams)
command 2>&1

# Redirect both stdout and stderr to a file
command > output.log 2>&1
# Short form (bash 4+)
command &> output.log

# Suppress all output (stdout + stderr)
command &> /dev/null

Usage

Stderr is separate from stdout. If you pipe a command, error messages are not captured unless you redirect stderr.

Other causes & fixes

Order matters — 2>&1 must come after >

# CORRECT — redirect stdout to file, then stderr to wherever stdout goes
command > file.log 2>&1

# WRONG — redirects stderr to the terminal (original stdout), then stdout to file
command 2>&1 > file.log

Capture only stderr (discard stdout)

# Redirect stdout to /dev/null, keep stderr visible
command 2>&1 1>/dev/null
# Short: redirect stdout to /dev/null, stderr to stdout
command 1>/dev/null

Append both streams to a log file

command >> output.log 2>&1

Capture command output into a variable

output=$(command 2>&1)
echo "Got: $output"

Pipe both output streams into another command

A pipe normally forwards stdout only. Put 2>&1 on the command before the pipe when stderr should be processed too.

# Send stdout and stderr to grep
command 2>&1 | grep -i "error"

# Keep the pipeline status meaningful when an earlier command fails
set -o pipefail

Keep stdout and stderr in separate files

Use separate file descriptors when a log consumer needs normal output and errors independently.

command > output.log 2> error.log

# Append instead of replacing existing logs
command >> output.log 2>> error.log