How to Use tee in Bash: Syntax and Examples

In bash, tee reads from standard input and writes the output to both a file and standard output. Use it by piping a command's output to tee filename to save and display the output at the same time.

Syntax

The basic syntax of tee is:

• command | tee [options] filename

Here, command is any command whose output you want to capture.

tee writes the output to filename and also sends it to the screen.

Common options include -a to append to the file instead of overwriting it.

bash

command | tee filename
command | tee -a filename

Example

This example shows how to list files and save the output to files.txt while also displaying it on the screen.

bash

ls -l | tee files.txt

Output

total 8
-rw-r--r-- 1 user user  0 Apr 27 12:00 files.txt
-rw-r--r-- 1 user user  123 Apr 27 11:59 example.sh

Common Pitfalls

One common mistake is forgetting that tee overwrites files by default, which can cause data loss.

Use -a to append instead.

Also, tee only captures standard output, so errors sent to standard error won't be saved unless redirected.

bash

echo "Hello" > file.txt
# Overwrites file.txt

echo "World" | tee file.txt
# Overwrites file.txt

echo "Again" | tee -a file.txt
# Appends to file.txt

# To capture errors:
command 2>&1 | tee output.log

Quick Reference

Option	Description
filename	File to write output to
-a	Append output to the file instead of overwriting
-i	Ignore interrupt signals
-p	Force output to the terminal even if stdout is redirected

Key Takeaways

Use tee to save command output to a file and display it simultaneously.

By default, tee overwrites files; use -a to append instead.

tee captures standard output only; redirect standard error if needed.

Combine tee with pipes to log outputs in scripts easily.