wait — Wait for child processes to finish

Linux / Service and process management / wait.html

A shell builtin that waits until child processes started by the shell have finished.

Basic Information

What is this command?

wait pauses a script until background children finish.

With a PID or job number it waits for that target only and returns its exit status.

What problems does it solve?

• Run the next step only after parallel jobs finish.
• Check the exit code of a background job.
• Ensure completion before cleaning temp files.
• Fan out to several hosts and collect results.

Key features

Wait for all

Without arguments it waits for all children.

• When to use: When waiting for all parallel jobs
• What you get: Execution continues after all children end
• Limitations: The status reflects the last target

Wait for a PID

A PID waits for that process only.

• When to use: When one job must complete
• What you get: That process exit status
• Limitations: An unknown PID fails immediately

Collecting exit codes

Use $? to read the result after each wait.

• When to use: When failures must be distinguished
• What you get: Per-job success or failure
• Limitations: Waiting on many keeps only the last status

Installation and usage

Check whether it is installed

help wait

man bash # wait is a shell builtin

Real-world examples

Wait for all

Wait until background jobs finish.

# Wait for every background job
wait

Wait for a PID

Wait for one PID.

# Wait for a specific child
bg_pid=$!
wait $bg_pid

Synchronize parallel jobs

Start several jobs and wait for all.

# Run three jobs in parallel, then wait
for h in web1 web2 web3; do ssh $h uptime & done
wait