Bash uses certain shell variables in the same way as the Bourne shell. In some cases, Bash assigns a default value to the variable.
cdbuiltin command. The value of this variable is also used by tilde expansion (see Tilde Expansion).
MAILPATHvariable is not set, Bash informs the user of the arrival of mail in the specified file or Maildir-format directory.
?’. When used in the text of the message,
$_expands to the name of the current mail file.
PATHindicates the current directory. A null directory name may appear as two adjacent colons, or as an initial or trailing colon.
\s-\v\$’. See Controlling the Prompt, for the complete list of escape sequences that are expanded before
PS2is expanded in the same way as
PS1before being displayed.