source | all docs for version 0.7.0 | all versions | oilshell.org

Warning: Work in progress! Leave feedback on Zulip or Github if you'd like this doc to be updated.

Oil Options

Use Option Groups To Gradually Opt In to Oil

This is how you opt into the Oil language:

shopt -s oil:all

It turns on:

• errexit, nounset (sh modes to get more errors)
• pipefail and inherit_errexit (bash modes to get more errors)
• Oil modes:
  • simple-word-eval (subsumes nullglob that strict:all includes)
  • more_errexit
  • strict-* (strict-array, etc.)
  • parse-* (parse-at, etc.)

When you care about running your script under other shells, use shopt -s strict:all, which is documented in the OSH manual.

That Affect Parsing

Options that affect parsing start with parse-.

• shopt -s parse-at enables splicing:

echo @words

and inline function calls.

echo @split(x)

See examples below.

shopt -s parse_brace does three things:

• allow builtins like cd to take a block (discussed in a recent thread)
• if, while/until, for, case not use curly brace delimiters instead of then/fi, do/done, etc. See below.
• To remove confusion, braces must be balanced inside a word. echo foo{ is an error. It has to be echo foo\{ or echo 'foo{'.
  • This is so that the syntax errors are better when you forget a space.
  • In a correct brace expansion, they're always balanced: echo {andy,bob}@example.com

Test cases start here:

https://github.com/oilshell/oil/blob/master/spec/oil-options.test.sh#L257

Examples:

if test -d / {
  echo one
} elif test -d /tmp {
  echo two
} else {
   echo none
}
# can also be put all on one line

while true {
  echo hi
  break
}

for x in a b c {
  echo $x
}

case $x {
  *.py)
    echo python
    ;;
  *.sh)
    echo shell
    ;;
}

What's the motivation for this? Mainly familiarity: I hear a lot of feedback that nobody can remember how to write an if statement or a for loop in shell. I believe this syntax is easier to remember, with the possible exception of case, which still has some shell legacy.

Spoiler: there will also be expression-based variants of each of these constructs:

if (x > 0) {
  echo hi
}
while (x > 0) {
  echo hi
}
for (x in @(a b c)) {
  echo $x
}

There is probably going to be switch/case or match/case, but that will likely come much later!

That Affect Runtime Behavior

• simple_echo. Changes the flags accepted by the echo builtin, and style of flag parsing. See the Builtins > echo below.

• simple-word-eval. Word evaluation consists of one stage rather than three:

  • No word splitting or empty elision. (In other words, arity isn't data-dependent.)
  • Static globbing, but no dynamic globbing. (In other words, data isn't re-parsed as code.)
  • This option is intended to be implemented by other shells.

TODO: copy examples from spec tests

echo $dir/*.py

• more_errexit. A error in a command sub can cause the parent shell to exit fatally. Also see inherit_errexit and strict_errexit.

Strict Option Produce More Errors

These options produce more programming errors. Importantly, the resulting program is still compatible with other shells.

For example, shopt -s strict-array produces runtime errors when you confuse strings and arrays. After you fix these problems, your program will still run correctly under bash.

In contrast, if you set shopt -s simple-word-eval (an option that doesn't start with strict-), the semantics of your program have changed, and you can no longer run it under other shells. It's considered an "Oil option": by setting it, you're upgrading to the Oil language.

See the OSH manual for a list of strict options and their meaning.