Gradually Upgrading Shell to Oil

The slogan of Oil is that it's *our upgrade path from bash to a better language and runtime.

How exactly does that work? This page will give you an idea. Written in response to this lobste.rs thread.

Step 1: Run osh myscript.sh

Your shell script should run as is. You most likely won't notice a difference, except perhaps better error messages when the script fails. (If you want gory details, see the Known Differences doc, but again these differences are small and rare.)

Optional: change the shebang line to something like #!/usr/local/bin/osh.

New Features

You can now start using features like var, const, setvar, and proc. You can just write them anywhere in the middle of your shell program!

const name = 'World'
var x = {greeting: "Hello $name"}  # A Python/JavaScript-like dictionary, with shell strings!

proc mycopy(src, dest) {        # named parameters!
  cp --verbose "$src" "$dest"   # You still need this quoting, which is ugly
}

mycopy mytest /tmp              # a proc is just like a shell function

(Note: early in Oil's life, the project was aiming for automatic translation from bash to Oil. This is no longer a goal, although the work could be revived by an interested party.)

Step 2: Add shopt --set oil:basic To the Top of Your Program

This breaks a few things, but opens up more features.

See Shell Language Deprecations

The most common one is probably subshell:

(cd /tmp; ls -l)             # No longer valid

forkwait { cd /tmp; ls -l }  # the new way to write subshells

cd /tmp { ls -l }            # Better

In exchange for changing your subshell syntax, you get Python-like expressions in if and while:

if (x > 0) {
  echo "$x is positive"
}

You don't have to remember how to type [ "$x" -gt 0 ] or [[ $x -gt 0 ]] or test "$x" -gt 0, or the differences between them. Oil has Python-like expressions.

Other changes:

• One of the biggest changes is Simple Word Evaluation. This means you can now write cp --verbose $src $dest without the quotes.
  • You can also splice an array with cp --verbose @list_of_files $dest. This doesn't mangle your filenames!
• If you had something like echo @foo in your shell script, you should change it to echo '@foo' to avoid invoking splicing. The @ is only special at the beginning of a word.

Step 3: Run with bin/oil

This breaks more things, and is still subject to change. That said, I encourage you to try it and tell me what happens! Dozens of people have given feedback on the language and improved it.

Where To Send Feedback

Related

• More motivation for upgrading at [Why Use Oil?]
• What Is Expected To Run Under OSH