source | all docs for version 0.9.9 | all versions | oilshell.org

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

Oil Language vs. Shell

This doc aims to help shell users understand Oil.

If you don't know shell, see A Tour of the Oil Language.

Strictness At Parse Time and Runtime

• Parse time: statically parsed.
• Runtime: Many strict_* shell options to reduce edge cases. Oil generally fails faster than shell.

There Are 3 Core Sublanguages Instead of 4

• Shell: Command, Word, Arith, Bool
• Oil: Command, Word, Expression (Python-Like Expressions)

Expressions Replace Arith and Bool

So Many Shell Constructs Are Deprecated/Discouraged.

All of this is discouraged in favor of Oil expressions:

• [[ $x =~ $pat ]]
• x=$(( x + 1 )) and (( x = x + 1 )) and let, etc.
• declare -A assoc=(['k1']=v1 ['k2']=v2)

For details on the expression language, see Oil's Expression Language (under construction).

See Oil Languages Idioms for more rewrites.

Command Language Differences

• Curly Braces instead of then fi and do done
• Procs and Blocks for Modularity
  • Shell functions are "upgraded" into procs, e.g. with named parameters
  • Ruby-like Blocks, and metaprogramming
• Keywords for Variables like var, const, setvar instead of builtins like local, readonly, myvar=foo, etc.
  • Array literals like var a = %(ale bean) instead of local a=(ale bean).
• Multiline strings replace here docs
• fork and forkwait builtins instead of & and (). Parentheses are generally used for Python-like expressions, e.g. if (x > 0) { echo 'positive' }

See A Tour of Oil and Command Language for more details.

Word Language Differences

• Simple Word Evaluation
  • Splicing with arrays
• Expression substitution like $[42 + a[i] + f(x)]
• Inline function calls like echo $join(['pea', nut'])
• You can write raw strings like echo r'C:\Program Files\'

See A Tour of Oil and Word Language for more details.

Runtime

Builtins

• Oil adds long flags like read --line
• Oil has builtin Functions

Shell Options, shvar, Registers

• shopts: shopt --set parse_brace
• shvars: IFS, _DIALECT
• Registers: _pipeline_status, _match(), etc.

Big Feature Categories

• Builtin sub with ${.myproc arg1 $x} (TODO)
• String Safety (TODO)
• Modules: for organizing code into files
• Metaprogramming with Blocks (TODO)

Some Shell Features That Oil Retains

Here's an incomplete list of bash features that are preserved:

• C-style strings like $'line\n'
• Brace expansion like {alice,bob}@example.com
• Process Substitution like diff <(sort left.txt) <(sort right.txt)

Related Links

• Oil Languages Idioms shows example of Oil and shell side by side.
• Shell Language Deprecations. These are breaking changes.
• Oil Expressions vs. Python