Pipes and Chaining Commands

Connecting Two Commands

The pipe operator | takes the stdout of the command on its left and feeds it as stdin to the command on its right. You can chain as many commands as you like this way.

Example: Connecting Two Commands

#!/bin/bash
printf "banana\napple\ncherry\n" | sort

Pipelines and Exit Status

By default, the exit status of a pipeline is the exit status of its last command, regardless of whether earlier commands failed. Enabling pipefail changes this so the pipeline fails if any stage fails.

Warning: Without pipefail, a broken first stage in a long pipeline can silently be ignored.

Example: Pipelines and Exit Status

#!/bin/bash
false | true
echo "default pipeline status: $?"

set -o pipefail
false | true
echo "pipefail status: $?"
set +o pipefail

Chaining with && and ||

&& runs the next command only if the previous one succeeded (exit status 0); || runs the next command only if the previous one failed (non-zero exit status). These are used constantly for lightweight conditional logic.

Example: Chaining with && and ||

#!/bin/bash
mkdir -p demo_dir && echo "directory ready"
rmdir demo_dir || echo "could not remove"

false || echo "this runs because the previous command failed"
true && echo "this runs because the previous command succeeded"

Building a Small Pipeline

Real scripts often chain several small, single-purpose tools together instead of writing one big command, which mirrors the Unix philosophy of composing simple programs.

Example: Building a Small Pipeline

#!/bin/bash
printf "3\n1\n2\n1\n3\n1\n" | sort -n | uniq -c