-H
Enable ‘!’ style history substitution (see Section 9.3 [History In- teraction], page 135). This option is on by default for interactive shells.
-P
If set, do not resolve symbolic links when performing commands such as cd which change the current directory. The physical direc- tory is used instead. By default, Bash follows the logical chain of directories when performing commands which change the current directory.
For example, if /usr/sys is a symbolic link to /usr/local/sys then:
$ cd /usr/sys; echo $PWD
/usr/sys
$ cd ..; pwd
/usr
If set -P is on, then:
$ cd /usr/sys; echo $PWD
/usr/local/sys
$ cd ..; pwd
/usr/local
-T
If set, any trap on DEBUG and RETURN are inherited by shell func- tions, command substitutions, and commands executed in a sub- shell environment. The DEBUG and RETURN traps are normally not inherited in such cases.
--
If no arguments follow this option, then the positional parame- ters are unset. Otherwise, the positional parameters are set to the arguments, even if some of them begin with a ‘-’.
-
Signal the end of options, cause all remaining arguments to be assigned to the positional parameters. The -x and -v options are turned off. If there are no arguments, the positional parameters remain unchanged.
Using ‘+’ rather than ‘-’ causes these options to be turned off. The options can also be used upon invocation of the shell. The current set of options may be found in $-.
The remaining N arguments are positional parameters and are assigned, in order, to $1, $2, . . . $N. The special parameter # is set to N.
The return status is always zero unless an invalid option is supplied.
4.3.2 The Shopt Builtin
This builtin allows you to change additional shell optional behavior. shopt shopt [-pqsu] [-o] [optname ...]
Toggle the values of settings controlling optional shell behavior. The settings can be either those listed below, or, if the -o option is used, those available with