Explanation: The command that is used to change options and positional parameters for a running Bash is set. The set command allows the user to modify the behavior of the shell by enabling or disabling various options, such as -x (trace mode), -e (exit on error), -u (treat unset variables as errors), and others. The set command can also be used to assign values to the positional parameters, which are the arguments passed to the shell or a shell script. The positional parameters are denoted by $1, $2, $3, and so on, up to $9. The special parameter 0referstothenameoftheshellortheshellscript.Thespecialparameter# refers to the number of positional parameters. The special parameter $@ refers to all the positional parameters as a list.
To change the positional parameters, the set command can be used with the – option, followed by the new arguments. For example, the following command will set the positional parameters to “a”, “b”, and “c”:
set – a b c
After this command, $1 will be “a”, $2 will be “b”, 3willbe"c",# will be 3, and $@ will be “a b c”. The – option signals the end of options and prevents any argument that starts with a - from being interpreted as an option. Alternatively, the set command can be used with the - option, followed by the new arguments. However, this will also disable the -x and -v options, if they were previously enabled. For example, the following command will set the positional parameters to “-a”, “-b”, and “-c”, and turn off the trace and verbose modes:
set - -a -b -c
The set command can also be used without any option or argument, in which case it will display the names and values of all shell variables and functions.
The other commands are not valid or relevant for changing options and positional parameters for a running Bash. The history command displays the history list of commands entered by the user. The bashconf command does not exist. The setsh command does not exist. The envsetup command does not exist.
References:
- [LPI Exam 101 Detailed Objectives], Topic 103: GNU and Unix Commands, Objective 103.1: Work on the command line, Weight: 4, Key Knowledge Areas: Use ofsetandunset.
- [Bash Reference Manual], Section 4.3: The Set Builtin.
