watch Command in Linux: Executing Commands Periodically

Imagine you want to monitor a situation by running a command periodically.

You can use bash history and manually run the program as many times as needed, or use the watch command in Linux.

The watch command in Linux executes a command periodically, allowing you to observe how the program's output changes over time.

If no interval is specified, watch uses 2 seconds by default.

The most common options are:

• -d        Shows the differences between updates;
• -n X    Sets the interval to X seconds;
• -t        Disables the header;
• -g       Exits when the command output changes;

In this example watch can be used to monitor TCP connections:

$ watch -n 1 ss -tEvery 1,0s: ss -t          Sun Sep 15 21:37:32 2019State   Local Address:Port         Peer Address:PortESTA        127.0.0.1:http            127.0.0.1:39608ESTAB       127.0.0.1:39608           127.0.0.1:http

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