elvish/pkg/eval/builtin_ns.go

package eval

import (
	"strconv"
	"syscall"

	"github.com/elves/elvish/pkg/eval/vars"
	"github.com/xiaq/persistent/vector"
)

//elvdoc:var _
//
// A blackhole variable.
//
// Values assigned to it will be discarded. Trying to use its value (like `put $_`)
// causes an exception.

//elvdoc:var args
//
// A list containing command-line arguments. Analogous to `argv` in some other
// languages. Examples:
//
// ```elvish-transcript
// ~> echo 'put $args' > args.elv
// ~> elvish args.elv foo -bar
// ▶ [foo -bar]
// ~> elvish -c 'put $args' foo -bar
// ▶ [foo -bar]
// ```
//
// As demonstrated above, this variable does not contain the name of the script
// used to invoke it. For that information, use the `src` command.
//
// @cf src

//elvdoc:var false
//
// The boolean false value.

//elvdoc:var ok
//
// The special value used by `?()` to signal absence of exceptions.

//elvdoc:var nil
//
// A special value useful for representing the lack of values.
//
// **WARNING**: Due to a bug, `$nil` cannot be used as a map key now.

//elvdoc:var paths
//
// A list of search paths, kept in sync with `$E:PATH`. It is easier to use than
// `$E:PATH`.

//elvdoc:var pid
//
// The process ID of the current Elvish process.

//elvdoc:var pwd
//
// The present working directory. Setting this variable has the same effect as
// `cd`. This variable is most useful in temporary assignment.
//
// Example:
//
// ```elvish
// ## Updates all git repositories
// for x [*/] {
// pwd=$x {
// if ?(test -d .git) {
// git pull
// }
// }
// }
// ```
//
// Etymology: the `pwd` command.

//elvdoc:var true
//
// The boolean true value.

var builtinNs = Ns{
	"_":     vars.NewBlackhole(),
	"pid":   vars.NewReadOnly(strconv.Itoa(syscall.Getpid())),
	"ok":    vars.NewReadOnly(OK),
	"nil":   vars.NewReadOnly(nil),
	"true":  vars.NewReadOnly(true),
	"false": vars.NewReadOnly(false),
	"paths": &EnvList{envName: "PATH"},
	"pwd":   PwdVariable{},
	"args":  vars.NewReadOnly(vector.Empty),
}

func addBuiltinFns(fns map[string]interface{}) {
	builtinNs.AddGoFns("", fns)
}