condexec

Conditionally shell out an exec

npm install condexec
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condexec

Conditionally shell out an exec

Installation

npm install condexec

Usage

var condexec = require('condexec');

var opts = {
  cwd: '/',
  onlyif: 'test -f /etc/passwd',
  notif: 'test -d /this/doesnt/exist',
  exec: 'echo "hello $USER you are in $PWD"'
};

condexec(opts, function(err) {
  console.log('done');
});

yields

hello dave you are in /
done

any and all output from the commands executed will be piped directly to the proper streams (stdout/stderr).

shell parsing

When the exec, onlyif, or notif attributes are given as strings, they are parsed by the shell before they are ran; they are executed as ['/bin/sh', '-c', '{string}']. Alternatively, you can pass an array of arguments instead of a string, which will allow you to bypass shell-parsing/word-splitting logic.

var file = '/etc/passwd';
var msg = 'this message has double"quotes and single\'quotes';
condexec({
  exec: ['echo', msg],
  onlyif: ['test', '-f', file]
});

yields

this message has double"quotes and single'quotes

Notice that you didn't need to worry about escaping the quotes before you passed them to exec.

error handling

When the callback is fired, it will contain what specifically produced an error.

var opts = {
  onlyif: 'test -d /etc/passwd',
  notif: 'test -f /aoehsutoehnaueohs/fake/fake/fake',
  exec: 'echo "hello $USER you are in $PWD"'
};

condexec(opts, function(err) {
  console.error(err.message);
});

yields

[onlyif] command `test -d /etc/passwd` returned with code 1

It tells you what command failed, in what clause, and with what code. Notice that, because the command failed, the exec line was never called.

debug

Pass in a debug attribute to see exactly what is happening

var opts = {
  debug: true,
  cwd: '/',
  onlyif: 'test -f /etc/passwd',
  notif: 'test -d /aoehsutoehnaueohs/fake/fake/fake',
  exec: 'echo "hello $USER you are in $PWD"'
};

condexec(opts, function(err) {
  console.log('success!');
});

yields

[onlyif] about to execute `test -f /etc/passwd`, expects 0
[onlyif] command `test -f /etc/passwd` returned with code 0
[notif] about to execute `test -d /aoehsutoehnaueohs/fake/fake/fake`, expects != 0
[notif] command `test -d /aoehsutoehnaueohs/fake/fake/fake` returned with code 1
[exec] about to execute `echo "hello $USER you are in $PWD"`, expects 0
hello dave you are in /
[exec] command `echo "hello $USER you are in $PWD"` returned with code 0
success!

Function

function condexec(options, callback(err))

options

  • exec: a string or array of commands to execute given the 2 optional conditions are satisfied
  • notif: an optional condition to meet before the exec command is run, expects this to return non-0
  • onlyif: an optional condition to meet before the exec command is run, expects this to return 0
  • debug: turn on debug output

This object is then passed into child_process.spawn, so pass in any options that you would like, such as cwd, env, etc.

callback

The callback runs when the conditional exec has finished, either successfully or with an error. The err object will be null if it was successful

License

MIT

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