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Is trap POSIX compliant?
Implementations may permit lowercase signal names as an extension. Trapping SIGKILL or SIGSTOP is syntactically accepted by some historical implementations, but it has no effect. Portable POSIX applications cannot attempt to trap these signals. The output format is not historical practice.
What is trap signal?
Trap allows you to catch signals and execute code when they occur. Signals are asynchronous notifications that are sent to your script when certain events occur. Most of these notifications are for events that you hope never happen, such as an invalid memory access or a bad system call.
How do I interrupt in bash?
You can press Ctrl-D to close the bash shell or open files when using cat command. You can press Ctrl-Z to suspend the current foreground process running in bash shell.
Which Posix signal is guaranteed to terminate a process?
The SIGKILL signal is sent to a process to cause it to terminate immediately (kill). In contrast to SIGTERM and SIGINT, this signal cannot be caught or ignored, and the receiving process cannot perform any clean-up upon receiving this signal.
What does the POSIX spec say about the trap?
The POSIX spec doesn’t say much about the conditions resulting in executing the EXIT trap, only about what its environment must look like when it is executed. In Busybox’s ash shell, your trap-exit test does not echo ‘TRAP’ before exiting due to either SIGINT or SIGTERM.
What should the exit status be in POSIX?
The exit status shall be n, if specified. Otherwise, the value shall be the exit value of the last command executed, or zero if no command was executed. When exit is executed in a trap action, the last command is considered to be the command that executed immediately preceding the trap action.
When to use TRAP…INT term exit?
Many examples for trap use trap INT TERM EXIT for cleanup tasks. But is it really necessary to list all the three sigspecs? If a SIGNAL_SPEC is EXIT (0) ARG is executed on exit from the shell. which I believe applies whether the script finished normally or it finished because it received SIGINT or SIGTERM.
How to keep exit status when trapping SIGINT?
# Eg 130 for SIGINT, 128 + (2 == SIGINT) echo “Doing signal-specific up” exit “$exit_status” } trap sig_handler INT HUP TERM QUIT If there is a separate EXIT trap, you can use the same methodology: immediately keep the exit status passed from the signal handler (if there is one) clean-up, then return the saved exit status.