5.1 Bourne Shell Variables
Bash uses certain shell variables in the same way as the Bourne shell.
In some cases, Bash assigns a default value to the variable.
A colon-separated list of directories used as a search path for
cd builtin command.
The current user's home directory; the default for the
The value of this variable is also used by tilde expansion
(see section 3.5.2 Tilde Expansion).
A list of characters that separate fields; used when the shell splits
words as part of expansion.
If this parameter is set to a filename and the
is not set, Bash informs the user of the arrival of mail in
the specified file.
A colon-separated list of filenames which the shell periodically checks
for new mail.
Each list entry can specify the message that is printed when new mail
arrives in the mail file by separating the file name from the message with
When used in the text of the message,
$_ expands to the name of
the current mail file.
The value of the last option argument processed by the
The index of the last option argument processed by the
A colon-separated list of directories in which the shell looks for
The primary prompt string. The default value is '\s-\v\$ '.
See section 6.9 Controlling the Prompt, for the complete list of escape
sequences that are expanded before
PS1 is displayed.
The secondary prompt string. The default value is '> '.