You can write if (x > 0) instead of if [ "$x" -gt 0 ].
You can pass blocks to commands, like cd /tmp { echo $PWD }
Simple Word Evaluation: You can write $var instead of "$var", and splice arrays with @myarray.
Reliable Error Handling becomes the default.
... and more

You can also use bin/osh indefinitely, in which case you don't need to read this doc. OSH is a highly compatible Unix shell.

Syntax Changes

Now onto the breakages. Most of them are unlikely, but worth noting.

`if ( )` and `while ( )` take expressions, not subshell commands

Code like if ( ls /tmp ) is valid shell, but it's almost always a misuse of the language. Parentheses mean subshell, not grouping as in C or Python.

In Oil:

Use if (x > 0) for true/false expressions
Use the forkwait builtin for subshells, which are uncommon. (It's like invoking the fork builtin, then the wait builtin.)

No:

( cd /tmp; rm *.sh )

Yes:

forkwait {
  cd /tmp
  rm *.sh
}

Better:

cd /tmp {  # no process created
  rm *.sh
}
echo $PWD  # restored

(Option parse_paren is part of group oil:upgrade.)

`@()` is spliced command sub, not extended glob

Oil doesn't have implicit word splitting, so we want @(seq 3) to be consistent with $(hostname). They're related in the same way that @myarray and $mystr are.

This means that @() is no longer extended glob, and ,() is an alias.

No:

echo @(*.cc|*.h)

Use this Oil alias instead:

echo ,(*.cc|*.h)

(Option parse_at is part of group oil:upgrade.)

`r'c:\Users\'` is a raw string, not joined strings

The meaning of \ within string literals can be confusing, so Oil distinguishes them like this:

$'foo\n'
- The $ prefix means that C-style backslash escapes are respected.
r'c:\Users\'
- The r prefix means the backslashes are literal.
- In shell this is written 'c:\Users\'. Oil accepts this in command mode for compatibility, but not expression mode.

The prefix changes the meaning of commands like:

echo r'foo'
# => foo in Oil
# => rfoo in shell, because of implicit joining

Instead, write 'rfoo' if that's what you mean.

(Option parse_raw_string is part of group oil:upgrade.)

Unsupported

Extended Globs in Word Evaluation

Like regular globs, the extended glob syntax is used in two ways:

Pattern matching
- case
- Bash boolean expressions like [[ x == !(*.cc|*.h) ]]
Word Evaluation
- commands like cp !(*.cc|*.h) /tmp
- arrays like local -a myarray=( !(*.cc|*.h) )
- Shell-style for loops

Extended globs are not supported in Simple Word Evaluation, so you can't use them in the second way after upgrading.

You may want to use the find command or Egg expressions instead.

(Option simple_word_eval is part of group oil:upgrade.)

More Quotes May Be Needed

With `oil:upgrade` Options

Option parse_at. In Oil, @ is used to splice arrays. To pass a string @foo to a command, quote it like '@foo'.

Option parse_brace. Braces after commands start block arguments. To change to a directory named {, quote it like cd '{'.

Option parse_equals. A statement like x = 42 is a "bare assignment" or attribute. To pass = to a command x, quote it like x '='.

Unconditionally

To avoid confusion with Oil's = operator, a word like =x can't be the first word in a command. To invoke such commands, quote them like '=x'.
Oil has new keywords like proc, const, var, and setvar. To use them as command names, quote them like 'proc'.

There is very little reason to use commands like '=x' and 'proc', so you will likely never run into this!

Summary

This concludes the list of features that's broken when you upgrade from OSH to Oil. We tried to keep this list as small as possible.

There are other features that are discouraged, like $(( x + 1 )), (( i++ )), [[ $s =~ $pat ]], and ${s%%prefix}. These have better alternatives in the Oil expression language, but they can still be used. See Oil vs. Shell Idioms.

Acknowledgments

Thank you to ca2013 for reviewing this doc.

Generated on Tue Mar 7 21:35:45 EST 2023

What Breaks When You Upgrade to Oil

Reasons for Upgrading