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Startup

This section describes how yash-rs is started and configured.

Command-line arguments

Start the shell by running the yash3 executable. The general syntax is:

yash3 [options] [file [arguments…]]
yash3 [options] -c command [command_name [arguments…]]
yash3 [options] -s [arguments…]

The shell’s behavior is determined by the options and operands you provide.

Options

The shell accepts shell options to control its behavior. The following options are only available at startup:

  • -c (--cmdline): Read and execute commands from the command operand.
  • -s (--stdin): Read and execute commands from standard input.
  • -i (--interactive): Force the shell to be interactive.
  • -l (--login): Make the shell a login shell. This can also be triggered by a leading hyphen in the command name (e.g., -yash3).
  • --profile <file>: Specify a profile file to execute.
  • --noprofile: Do not execute any profile file.
  • --rcfile <file>: Specify an rcfile to execute.
  • --norcfile: Do not execute any rcfile.

Modes of operation

The shell has three modes:

  • File mode: If neither -c nor -s is specified, the first operand is treated as the path to a script file to execute. Any following operands become positional parameters for the script.
  • Command string mode: With -c, the shell executes the command string given as the first operand. If command_name is specified, it sets the special parameter 0. Remaining operands become positional parameters.
  • Standard input mode: With -s, the shell reads commands from standard input. Any operands are set as positional parameters.

If no operands are given and -c is not specified, the shell assumes -s.

Initialization files

When the shell starts, it may execute one or more initialization files to configure the environment.

Login shell

If the shell is a login shell (started with -l or a leading hyphen in its name), it executes a profile file. The path can be set with --profile. Use --noprofile to skip the profile file.

⚠️ Profile file execution is not yet implemented.

Interactive shell

If the shell is interactive, it executes an rcfile. The path can be set with --rcfile. Use --norcfile to skip the rcfile.

If no rcfile is specified, the shell checks the ENV environment variable. If set, its value is expanded for parameter expansion, command substitution, and arithmetic expansion, and used as the rcfile path.

The rcfile is only executed if:

  • The shell is interactive.
  • The real user ID matches the effective user ID.
  • The real group ID matches the effective group ID.

Compatibility

Options for initialization files (--profile, --noprofile, --rcfile, --norcfile) are not part of POSIX.1-2024 and may not be available in other shells. See Compatibility in the options documentation for portable shell options.

POSIX.1-2024 does not specify login shells or profile files. The behavior described here is specific to yash-rs and may differ from other shells.

Using the ENV environment variable for initialization files is POSIX-specified. In the future, yash-rs may support a different default rcfile location depending on a shell option.