meaning of trap "" HUP

[jaigs_27]

I am a beginner in scripting and following is written on the top of my script

trap "" HUP
Can an one help me in understanding this?

Thanks

[wowbag1]

trap is a builtin command used for specifying the actions to take on receipt of signals.
so:
trap HUP means Hang up; usually sent when a terminal goes off line, or a user logs out.

Hope this helps.

[wje_lf]

This means "In this script, ignore the hangup signal."

For an introduction to signals, and a list of signals, see this.

You could also have spelled this as

trap "" SIGHUP

bash scripts normally stop running and emit "Hangup" to the screen and stop running when they receive a hangup signal. The statement you asked about causes this signal to be ignored. You can put something between the quotes if you wish; that will be a bash statement to execute upon receiving the hangup signal. It can be as simple as printing the content of some variables, or it can be the invocation of some other script, or it can be almost anything.

In addition to signals, you can also say things like

trap "somethingsomething" EXIT

to run some command upon exit from your script.

Hope this helps.

[jaigs_27]

Thanks, now understood