watch

Execute a command every 2 seconds (default)

$ watch [command]

$ watch -n [5] [command]

$ watch -d [command]

$ watch -g [command]

$ watch -t [command]

$ watch -b [command]

$ watch -c [ls --color=always]

$ watch -e [command]

watch [options] command

watch executes a command repeatedly, displaying output in full-screen mode. This allows monitoring of changing data such as disk usage, running processes, or log files without manually re-running commands.
By default, the command runs every 2 seconds. The header displays the interval, command, and current time. Use -d to highlight what changed between updates—useful for spotting modifications in large output.
The command is passed to sh -c, so shell features like pipes and redirects work but may require quoting. Non-printing characters are stripped; use cat -v in the pipeline to see them.

-n, --interval SECS

Update interval in seconds (default: 2, min: 0.1)

Highlight differences; permanent shows all changes since start

Exit when output changes

Freeze on error and exit after key press

Beep on non-zero exit code

Interpret ANSI color sequences

Do not interpret ANSI color sequences

Hide header (interval, command, time)

Disable line wrapping

Run command at precise intervals from start time

Scroll output like tail -f instead of clearing

Pass command to exec instead of sh -c

Show help

Show version

Commands with special characters may need extra quoting due to shell interpretation. POSIX option processing stops at the first non-option argument, so flags after the command aren't processed by watch. Very fast intervals may cause high CPU usage. The -c option is needed for colored output from commands like ls --color.

The watch command was written by Tony Rems and became part of the procps package (later procps-ng) for Linux. It provides a simple alternative to writing custom loops for monitoring command output. The concept of periodically executing and displaying a command's output has been implemented in various forms across Unix systems.

tail(1), top(1), htop(1), while(1)