Open Editor From Command Line and Fetch Input

Question

I'm currently working on a feature for CocoaPods, a Ruby gem. There's an existing command that accepts a number of options. I'd like to add an extra option that enables the user to enter a custom message by opening the default text editor and, when the user saves and quits the editor, the message is fed to the command that was executed.

What I want to replicate is how you can add -m to the git commit command to have you enter a commit message. I have little experience with creating command line tools so any help is much appreciated.

The goal is to execute a specific command command --message, open the editor, have the user enter a custom message, and execute the command with the custom message being one of the arguments stored in argv.

The interactive_editor gem seems related to what you try to achieve. I did not check the source, but there might be ideas to pick there. — Eric Platon
– Eric Platon, Commented Nov 21, 2015 at 2:40

Aleksei Matiushkin · Accepted Answer · 2015-11-20 17:04:20Z

2

The common workflow is:

the caller application creates a temporary file;
determines the default editor (for Debian-based it would be /usr/bin/editor, for other linuces — the content of shell variable $EDITOR, etc);
runs a shell command in a subshell with Kernel#system (not with backticks!);
waits for it to exit;
determines the exit code, and skips following if it is not 0;
reads the content of temporary file, created in step 1 and removes this file.

In ruby that would be like:

▶ f = Tempfile.new 'cocoapods'
#⇒ #<File:/tmp/am/cocoapods20151120-6901-u2lubx>
-rw------- 1 am am 0 nov 20 15:03 /tmp/am/cocoapods20151120-6901-u2lubx
▶ path = f.path
#⇒ "/tmp/am/cocoapods20151120-6901-u2lubx"
▶ f.puts 'This content is already presented in file'
#⇒ nil
▶ f.close # HERE MUST BE ENSURE BLOCK, BUT FOR THE SAKE OF AN EXAMPLE...
#⇒ nil
▶ system "editor #{path}"
#⇒ Vim: Warning: Output is not to a terminal

If you are testing this in console, just type anything, followed by Esc:wq. In real life there will be normal vim (or what the default editor is) opened.

▶ File.read path
#⇒ "GGGGGGGGGThis content is already presented in file\n"

All together:

#!/usr/bin/env ruby

require 'tempfile'

f = Tempfile.new 'cocoapods'
path = f.path
f.puts 'This content is already presented in file'
f.close # HERE MUST BE ENSURE BLOCK, BUT FOR THE SAKE OF AN EXAMPLE...
system "editor #{path}"
puts File.read path

edited Nov 20, 2015 at 17:04

answered Nov 20, 2015 at 14:10

Aleksei Matiushkin

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2 Comments

Bart Jacobs Over a year ago

That's a great start. The problem I'm running into is getting the contents of the file before the Ruby script exits. The Ruby script exits when the editor is opened. I was hoping/expecting that it would continue its execution the moment the editor is closed. You write File.read path. Where do you read the contents of the temporary file?

Aleksei Matiushkin Over a year ago

Oh, sorry, I messed things up: to invoke an editor in the same context (in a subshell,) one should use Kernel#system rather that backticks. I updated an answer with the code of the whole script for your convenience.

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