trap - Trap signals

trap [ action condition ... ]

trap -p [ condition ... ]

trap -l

Description

The trap utility sets the action for qsh to take when a condition arises. qsh expands action once when running trap and again when condition arises.

When the -p option is specified, trap displays the current action for the specified conditions.

When the -l option is specified, trap displays a list of all of the signal names and their corresponding numbers.

When no arguments are specified, trap displays a list of the currently defined traps.

Options

-l

Display a list of all of the signal names and their corresponding numbers.

-p

Display each trap in a re-enterable format.

Operands

For action, you can specify:

• Null to ignore condition when it arises
• Minus (-) to reset condition to its original value.
• A command to be run each time condition arises.

For condition, you can specify:

• Name or number of a signal. You can use trap -l to display a list of valid signals. For portability, you should always specify the signal name.
• 0 or EXIT. qsh runs action when the shell exits.
• ERR. qsh runs action when a command has a non-zero exit status.
• DEBUG. qsh runs action after each simple command.

If more than one condition arises at the same time, qsh runs the traps in this order:

1. DEBUG, if it is specified, then
2. ERR, if it is specified and applicable, then
3. Any other specified traps in signal number order, then
4. EXIT.

Exit Status

• 0 when successful.
• >0 when an invalid condition is specified.

Related information

• kill - Terminate or signal processes
• wait - Wait for process completion

1. Set a trap for the ERR condition:

   trap `print Command failed' ERR
   

2. Ignore the ERR condition:

   trap "" ERR
   

3. Reset the ERR condition to its original value:

   trap - ERR
   

4. Display the current action for the ERR condition:

   trap -p ERR
   

5. Display all of the currently defined traps:

   trap