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This chapter describes new YSH keywords in the command language.

(in progress)

Assignment

const

Binds a name to a YSH expression on the right, with a dynamic check to prevent mutation.

const c = 'mystr'        # equivalent to readonly c=mystr
const pat = / digit+ /   # an eggex, with no shell equivalent

If you try to re-declare or mutate the name, the shell will fail with a runtime error. const uses the same mechanism as the readonly builtin.

Consts should only appear at the top-level, and can't appear within proc or func.

var

Initializes a name to a YSH expression.

var s = 'mystr'        # equivalent to declare s=mystr
var pat = / digit+ /   # an eggex, with no shell equivalent

It's either global or scoped to the current function.

You can bind multiple variables:

var flag, i = parseArgs(spec, ARGV)

var x, y = 42, 43

You can omit the right-hand side:

var x, y  # implicitly initialized to null

setvar

At the top-level, setvar creates or mutates a variable.

setvar gFoo = 'mutable'

Inside a func or proc, it mutates a local variable declared with var.

proc p {
  var x = 42
  setvar x = 43
}

You can mutate a List location:

setvar a[42] = 'foo'

Or a Dict location:

setvar d['key'] = 43
setvar d.key = 43  # same thing

You can use any of these these augmented assignment operators

+=   -=   *=   /=   **=   //=   %=
&=   |=   ^=   <<=   >>=

Examples:

setvar x += 2  # increment by 2

setvar a[42] *= 2  # multiply by 2

setvar d.flags |= 0b0010_000  # set a flag

setglobal

Creates or mutates a global variable. Has the same syntax as setvar.

Expression

equal

The = keyword evaluates an expression and shows the result:

oil$ = 1 + 2*3
(Int)   7

It's meant to be used interactively. Think of it as an assignment with no variable on the left.

call

The call keyword evaluates an expression and throws away the result:

var x = :| one two |
call x->append('three')
call x->append(['typed', 'data'])

Definitions

proc

Procs are shell-like functions, but with named parameters, and without dynamic scope.

Here's a simple proc:

proc my-cp (src, dest) {
  cp --verbose --verbose $src $dest
}

Here's the most general form:

proc p (
  w1, w2, ...rest_words;
  t1, t2, ...rest_typed;
  n1, n2, ...rest_named;
  block) {

  = w1
  = t1
  = n1
  = block
}

See the Guide to Procs and Funcs for details.

Compare with sh-func.

func

Define pure functions, in the style of Python and JavaScript:

func add(x, y) {
  return (x + y)
}

echo $[add(3, 2)]  # => 5

See the Guide to Procs and Funcs for details.

ysh-return

To return an expression, wrap it in () as usual:

func inc(x) {
  return (x + 1)
}