= Invocation
:encoding: UTF-8
:lang: en
//:title: Yash manual - Invocation
:description: This page describes how yash is initialized when invoked.

When invoked as a program, yash performs the predefined initialization steps
and repeatedly reads and executed commands. Command line arguments given in
the invocation determines how the shell initializes itself and executes
commands.

[[arguments]]
== Command line arguments

The syntax of command line arguments for yash conforms to POSIX. As defined in
POSIX, arguments are separated into dfn:[options] and dfn:[operands]. For more
detailed explanation about options and operands, see
link:builtin.html#argsyntax[Command argument syntax]. All options must come
before operands. The interpretation of operands depends on options specified.

When you specify the +-c+ (+--cmdline+) option, you must give at least one
operand. The shell interprets and executes the first operand as a command
string. The second operand, if any, is used to initialize the
link:params.html#sp-zero[+0+ special parameter].
The other operands, if any, are used to initialize the
link:params.html#positional[positional parameters].
When the +-c+ (+--cmdline+) option is specified, the shell does not read any
file or the standard input (unless the link:_dot.html[dot built-in] is used).

If you specify the +-s+ (+--stdin+) option, the shell reads the standard
input, interprets the input as commands, and executes them. All the operands
given are used to initialize the link:params.html#positional[positional
parameters].
The link:params.html#sp-zero[+0+ special parameter] is initialized to the name
the shell is invoked as.

If you specify neither the +-c+ (+--cmdline+) nor +-s+ (+--stdin+) option, the
shell reads a file, interprets the file contents as commands, and executes
them. The first operand specifies the pathname of the file. The remaining
operands are used to initialize the link:params.html#positional[positional
parameters].
If you do not give any operands, the shell reads the standard input as if the
+-s+ (+--stdin+) option is specified.

You cannot use both the +-c+ (+--cmdline+) and +-s+ (+--stdin+) options at a
time.

If you specify either the +--help+ or +--version+ option, the shell never
performs the usual initialization or command execution. Instead, it just
prints brief usage (for +--help+) or version information (for +--version+). If
the +--version+ option is accompanied by the +-v+ (+--verbose+) option, the
shell prints a list of the available optional features as well.

If you specify the +-i+ (+--interactive+) option, the shell goes into the
link:interact.html[interactive mode].
If you specify the `+i` (`++interactive`) option, conversely, the shell never
goes into the interactive mode.

If you specify the +-l+ (+--login+) option, the shell behaves as a login
shell.

The +--noprofile+, +--norcfile+, +--profile+, and +--rcfile+ options determine
how the shell is initialized (see below for details).

In addition to the options described above, you can specify options that can
be specified to the link:_set.html[set built-in].

If the first operand is +-+ and the options and the operands are not separated
by +--+, the first operand is ignored.

[[init]]
== Initialization of yash

Yash initializes itself as follows:

. Yash first parses the name it was invoked as. If the name starts with +-+,
  the shell behaves as a login shell. If the name is +sh+ (including names
  such as +/bin/sh+), the shell goes into the link:posix.html[POSIXly-correct
  mode].
. If no operands are given and the standard input and standard error are both
  connected to a terminal, the shell goes into the
  link:interact.html[interactive mode] unless the `+i` (`++interactive`)
  option is specified.
. link:job.html[Job control] is automatically enabled in an interactive shell
  unless the `+m` (`++monitor`) option is specified.
. Yash reads and executes commands from the following files (unless the real
  and effective user IDs of the shell process are different or the real and
  effective group IDs of the shell process are different):
 .. If it is behaving as a login shell, the shell reads the file specified by
    the +--profile={{filename}}+ option unless the +--noprofile+ option is
    specified or the shell is in the link:posix.html[POSIXly-correct mode].
    +
    If the +--profile={{filename}}+ option is not specified, the shell reads
    link:expand.html#tilde[~]/.yash_profile as a default.
 .. If in the interactive mode, the shell reads the file specified by the
    +--rcfile={{filename}}+ option unless the +--norcfile+ option is specified.
    +
    If the +--rcfile={{filename}}+ option is not specified, the shell
    - reads link:expand.html#tilde[~]/.yashrc as a default if not in the
      POSIXly-correct mode; or
    - performs link:expand.html[parameter expansion] on the value of the
      link:params.html#sv-env[+ENV+ environment variable] and treats the
      expansion result as the name of the file to read if in the
      POSIXly-correct mode.

[NOTE]
Yash never automatically reads /etc/profile, /etc/yashrc, nor
link:expand.html#tilde[~]/.profile.

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