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Syntactic Concepts in Oil

Shell has these concepts.

Sigils:

echo $var
echo "$@"

Sigil Pairs:

echo ${var} 
echo $(hostname)  #
echo $((1 + 2 ))

Oil extends them.

Static Parsing

Like Python, JS. See Oil language definition.

• [[ ]] and []

• echo -e and $''

• remaining dynamic parsing in shell

  • printf
  • glob

• arithmetic is still somewhat dynamic -- replaced by Oil expressions

• assignment builtins support dynamism, replaced by var and setvar

Parsing Options to Take Over @, (), {}, set, and maybe =

Another concept is parsing modes.

shopt -s all:oil  # most important thing, turns on many options

if ( ) {
}

echo @array

set x = 1
builtin set -o errexit

equals:

x = 1
equivalent to 
const x = 1

This is for Oil as a configuration language.

Command vs. Expression Mode

See Command vs. Expression Mode.

echo hi

Expression mode in three places:

echo @array
myprog --flag=$f(x, y)
var z = f(x+1, y)

Control FLow:

if grep foo if (foo) {} # replaces if [ -n $foo ]; then

while

for

switch/case -- for translation to C++ like mycpp match/case

Sigils, Sigil Pairs, and Lexer Modes

Sigils:

• $foo for string
• @array for array of strings
• : sort of means "code" ?

Sigil Pairs:

• ${x} for word evaluation

• $(( )) for shell arithmetic is deprecated

• $(bare words) for command sub

• %(bare words) for shell arrays

• %[1 2 3] for typed arrays

• %{ } for table literals / embedded TSV

• $// for regexes

• c'' c"" r'' r"" for strings

  • legacy: $'' in command mode

• :{} for blocks

• :() for unevaluated expressions

Table example:

var people = %{
  name      age:Int
  bob       10_000
  'andy c'  15_000
}
var people = {name: %(bob 'andy c'), age: %[10_000 15_000]}

• maybe: #() for tuple?

Sigil pairs often change the lexer mode.