Add isNonzeroExitCode to Processes

[sleberknight]

Processes contains the isSuccessfulExitCode method which works well when you are checking the positive case:

if (Processes.isSuccessfulExitCode(exitCode)) {
  // handle success
}

But when checking the negative case it would not be too hard to miss the ! in front of Processes assuming you're not using a static import:

if (!Processes.isSuccessfulExitCode(exitCode)) {
  // handle a nonzero exit
}

This issue adds a new isNonzeroExitCode method to Processes to specifically indicate the exit code is nonzero, and not necessarily a failure or unsuccessful termination. For example, according to Exit Codes With Special Meanings in TLDP (The Linux Documentation Project), a code of 130 represents termination due to a user pressing CTRL+C. So, is that really a program failure or error? I would argue it's not necessarily a problem with the program, e.g. a user terminates a long-running command using CTRL+C instead of letting it finish normally. In Exit and Exit Status, TLDP also says:

A successful command returns a 0, while an unsuccessful one returns a non-zero value that usually can be interpreted as an error code.

The key word here is usually, leaving room for a nonzero exit code that isn't necessarily an error. So, using the generic isNonzeroExitCode seems like a decent and clear choice here.

So the above "negative" example will now become:

if (Processes.isNonzeroExitCode(exitCode)) {
  // handle a nonzero exit
}

[sleberknight]

Some additional references:

• Linux and Unix exit code tutorial with examples
• Advanced Bash-Scripting Guide: Chapter 6. Exit and Exit Status
• Advanced Bash-Scripting Guide: Appendix E. Exit Codes With Special Meanings
• Exit Status (Wikipedia)