| (Pipe)

command1 | command2 | command3 ...

Use xargs to pass pipe output as arguments.

command1 | xargs command2

Syntax	Description
cmd1 | cmd2	Passes the standard output of cmd1 to the standard input of cmd2.
cmd1 |& cmd2	Passes both standard output and standard error to cmd2 (Bash 4+).
cmd1 2>&1 | cmd2	Merges standard error into standard output and passes both to cmd2.
cmd1 | tee file | cmd2	Saves the output of cmd1 to a file while also passing it to cmd2.
cmd1 | xargs cmd2	Passes the output of cmd1 as arguments to cmd2 (one argument per line).
cmd1 | xargs -I{} cmd2 {}	Runs cmd2 for each line, substituting the line into the {} placeholder.
${PIPESTATUS[@]}	Returns the exit status of each command in the pipeline as an array.

The following examples use this file.

fruits.txt

cherry
apple
banana
apple
cherry

Sort the lines in a file and remove duplicates. sort orders the lines, then uniq removes consecutive duplicate lines.

cat fruits.txt | sort | uniq
apple
banana
cherry

Use grep to extract only error lines from a log file, then display the last 10.

grep "ERROR" app.log | tail -10
2026-03-06 09:15:22 ERROR: Connection refused
2026-03-06 09:18:03 ERROR: Timeout exceeded

Check running nginx processes. The key is using grep -v grep to exclude the grep process itself from the results.

ps aux | grep nginx | grep -v grep
www-data  1234  0.0  0.2  55840  4096 ?  Ss  10:00  0:00 nginx: master
www-data  1235  0.0  0.1  55840  2048 ?  S   10:00  0:00 nginx: worker

Count the number of files in the current directory.

ls | wc -l
42

Display the top 10 entries by disk usage, largest first.

du -sh * | sort -h | tail -10

Pipe standard error along with standard output, and use tee to also save everything to a log file.

make 2>&1 | tee build.log | grep -E "error|warning"

Use find to locate files and xargs to convert the results into arguments for deletion.

find . -name "*.tmp" | xargs rm

Use ${PIPESTATUS[@]} to check the exit status of each command in the pipeline.

cat fruits.txt | grep "apple" | wc -l
2
echo ${PIPESTATUS[@]}
0 0 0

A pipe (|) runs each command in a separate process in parallel, making it very efficient. However, if you assign a value to a shell variable inside a pipe, that variable is not accessible outside the pipe because each segment runs in its own subshell. To capture output into a variable, use command substitution ($()) instead.

To save output to a file while also passing it to the next command, see tee.