Command prompt
When an interactive shell reads input, it displays a command prompt—a string indicating that the shell is ready to accept commands. The prompt can be customized to display information such as the current working directory, username, or hostname.
Customizing the command prompt
The command prompt is controlled by the PS1 and PS2 variables:
PS1defines the primary prompt, shown when the shell is ready for a new command.PS2defines the secondary prompt, shown when the shell expects more input to complete a command (i.e., when a command spans multiple lines).
Each time the shell displays a prompt, it performs parameter expansion, command substitution, and arithmetic expansion on the prompt strings. This allows prompts to include dynamic information, such as the working directory or username.
After these expansions, the shell performs exclamation mark expansion (see below) on the PS1 prompt. PS2 is not subject to exclamation mark expansion.
The default values for these variables are:
PS1='$ '
PS2='> '
Many shells change the default PS1 to # for the root user, but yash-rs does not yet support this.
Custom prompts are usually set in the rcfile. For example, to include the username, hostname, and working directory in the prompt, add this to your rcfile:
PS1='${LOGNAME}@${HOSTNAME}:${PWD} $ '
You do not need to export PS1 or PS2 for them to take effect.
Exclamation mark expansion
Exclamation mark expansion replaces an exclamation mark (!) in the PS1 prompt with the history number of the next command. However, yash-rs does not yet support command history, so this feature is currently non-functional.
To include a literal exclamation mark in the prompt, use a double exclamation mark (!!).
Compatibility
POSIX.1-2024 allows shells to perform exclamation mark expansion before other expansions, in which case exclamation marks produced by those expansions are not replaced.
Additional special notation that starts with a backslash (\), supported by earlier versions of yash, is not yet implemented in yash-rs.