Output Redirection

Intermediate~20 min read

Control where output goes using redirection operators. Separate stdout from stderr, append to files, or discard noise.

Stdout and Stderr

Output

Click Run to execute your code

Note: 1> is stdout, 2> is stderr. 2>&1 merges stderr into stdout.

Pro Tip: Send diagnostic messages to stderr: echo "error" 1>&2.

Caution: Overwriting files with > is destructive. Use >> to append.

# Wrong
cmd 2>&1 > out.txt
# Correct
cmd > out.txt 2>&1

# Wrong (overwrites)
echo data > file
# Safer append
echo data >> file

Task: Run a command that writes to both stdout and stderr, saving each to separate files. Then produce a combined file with both.

Output

Click Run to execute your code

Show Solution

{ echo out; echo err 1>&2; } 1>out.txt 2>err.txt
{ echo out; echo err 1>&2; } > both.txt 2>&1

Chain commands to transform data using Pipes.