onSignalReceived

Trap OS signals

Description

onSignalReceived events are triggered by OS signals.

The following quote from Wikipedia explains what signals are:

Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling. They are a limited form of inter-process communication (IPC), typically used in Unix, Unix-like, and other POSIX-compliant operating systems.

A signal is an asynchronous notification sent to a process or to a specific thread within the same process to notify it of an event. Common uses of signals are to interrupt, suspend, terminate or kill a process.

This event is designed to be used in shell scripts. While this event can be used with the shell in interactive mode (ie from the REPL prompt), this might result in unexpected behaviour. Thus it is only recommended to use onSignalReceived for shell scripts.

Usage

event onSignalReceived name=SIGNAL { code block }

!event onSignalReceived [SIGNAL]name

Valid Interrupts

• SIGHUP"Signal hangup" -- triggered when a controlling terminal is closed (eg the terminal emulator closed)
• SIGINT"Signal interrupt" -- triggered when a user interrupts a process, typically via ctrl+c
• SIGQUIT"Signal quit" -- when the user requests that the process quits and performs a core dump
• SIGTERM"Signal terminate" -- triggered by a request for a processes termination. Similar to SIGINT
• SIGUSR1"Signal user 1" -- user defined
• SIGUSR2"Signal user 2" -- user defined
• SIGWINCH"Signal window change" -- triggered when the TTY (eg terminal emulator) is resized

Payload

The following payload is passed to the function via STDIN:

{
    "Name": "",
    "Interrupt": {
        "Name": "",
        "Signal": ""
    }
}

Name

This is the namespaced name -- ie the name and operation.

Interrupt/Name

This is the name you specified when defining the event.

Signal

This is the signal you specified when defining the event.

Valid interrupt operation values are specified below. All interrupts / signals are UPPERCASE strings.

Examples

Interrupt 'SIGINT':

event onSignalReceived example=SIGINT {
    out "SIGINT received, not quitting"
}

Detail

The interrupts listed above are a subset of what is supported on each operating system. Please consult your operating systems docs for details on each signal and what their function is.

Windows Support

While Windows doesn't officially support signals, the following POSIX signals are emulated:

var interrupts = map[string]syscall.Signal{
	"SIGHUP":  syscall.SIGHUP,
	"SIGINT":  syscall.SIGINT,
	"SIGQUIT": syscall.SIGQUIT,
	"SIGILL":  syscall.SIGILL,
	"SIGTRAP": syscall.SIGTRAP,
	"SIGABRT": syscall.SIGABRT,
	"SIGBUS":  syscall.SIGBUS,
	"SIGFPE":  syscall.SIGFPE,
	"SIGKILL": syscall.SIGKILL,
	"SIGSEGV": syscall.SIGSEGV,
	"SIGPIPE": syscall.SIGPIPE,
	"SIGALRM": syscall.SIGALRM,
	"SIGTERM": syscall.SIGTERM,
}

Plan 9 Support

Plan 9 is not supported.

Stdout

Stdout is written to the terminal. So this can be used to provide multiple additional lines to the prompt since readline only supports one line for the prompt itself and three extra lines for the hint text.

Order of execution

Interrupts are run in alphabetical order. So an event named "alfa" would run before an event named "zulu". If you are writing multiple events and the order of execution matters, then you can prefix the names with a number, eg 10_jump

Namespacing

The onSignalReceived event differs a little from other events when it comes to the namespacing of interrupts. Typically you cannot have multiple interrupts with the same name for an event. However with onPrompt their names are further namespaced by the interrupt name. In layman's terms this means example=SIGINT wouldn't overwrite example=SIGQUIT.

The reason for this namespacing is because, unlike other events, you might legitimately want the same name for different interrupts.

See Also

• Interactive Shell: What's different about Murex's interactive shell?
• Terminal Hotkeys: A list of all the terminal hotkeys and their uses
• event: Event driven programming for shell scripts
• onCommandCompletion: Trigger an event upon a command's completion
• onPrompt: Events triggered by changes in state of the interactive shell
• signal: Sends a signal RPC

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This document was generated from builtins/events/onSignalReceived/signaltrap_doc.yaml.