LPI 101-500 Actual Questions

The command that will reduce all consecutive spaces down to a single space is tr -s ’ ’ < a.txt > b.txt. This command uses the following options and syntax:

-s: Squeezes repeated characters listed in the first set with single occurrence.

’ ': Specifies a space character as the first set.

< a.txt: Redirects the input from a file named a.txt.

b.txt: Redirects the output to a file named b.txt.

The output of this command will be a new file called b.txt that contains the same text as a.txt, except that any sequence of multiple spaces will be replaced by a single space. For example, if the file a.txt contains the following text:

This is a text file with multiple spaces.

The file b.txt will contain the following text:

This is a text file with multiple spaces.

The other commands are incorrect for the following reasons:

A. tr ‘\s’ ’ ’ < a.txt > b.txt: This command will replace every whitespace character (\s) with a space character, which will not reduce the number of spaces, but rather convert tabs and newlines into spaces.

B. tr -c ’ ’ < a.txt > b.txt: This command will complement the first set, meaning that it will apply the operation to all characters that are not spaces. This will not affect the spaces at all, but rather squeeze all other characters.

C. tr -d ’ ’ < a.txt > b.txt: This command will delete all spaces from the input, which will not reduce them to a single space, but rather remove them completely.

D. tr -r ’ ’ ‘\n’ < a.txt > b.txt: This command will replace all spaces with newlines, which will not reduce the spaces, but rather create a new line for each word.

 The tail command prints the last part of a file to the standard output. The -n option specifies the number of lines to print. Therefore, tail -n 10 filename will print the last 10 lines of the file named filename. The other commands are either invalid or do not perform the desired task. The cat command concatenates files and prints them to the standard output, but it does not have a -n option. The dump command is used to backup filesystems, not to print files. The head command prints the first part of a file, not the last part. References:

LPIC-1 Exam 101 Objectives, Topic 103: GNU and Unix Commands, 103.3 Perform basic file management

LPIC-1 Linux Administrator 101-500 Exam FAQ, LPIC-1 Exam 101 Objectives, GNU and Unix Commands (Total Weight: 25)

The .bash_history file, located in the user home directory, is used to store the Bash history. The Bash history is a list of commands that the user has entered in the Bash shell. The .bash_history file is created when the user first starts a Bash session, and is updated when the user exits the session or runs the history command with the -a or -w option. The user can view the contents of the .bash_history file with the cat command, or use the history command to see the numbered list of commands. The user can also edit, delete, or clear the .bash_history file with various commands and options. The location and name of the history file can be changed by setting the HISTFILE environment variable to a different value. 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 of history and HISTFILE.

Where is bash’s history stored?, Topic: Bash maintains the list of commands internally in memory while it’s running.

QUESTIONNO: 26

Which Bash environment variable defines in which file the user history is stored when exiting a Bash process? (Specify ONLY the variable name.)

Answer: HISTFILE

The HISTFILE environment variable defines in which file the user history is stored when exiting a Bash process. The user history is a list of commands that the user has entered in the Bash shell. By default, the HISTFILE variable is set to ~/.bash_history, which means that the history is stored in a hidden file called .bash_history in the user’s home directory. The user can change the value of the HISTFILE variable to store the history in a different file or location. For example, the following command will set the HISTFILE variable to ~/my_history:

export HISTFILE=~/my_history

This will cause the history to be stored in a file called my_history in the user’s home directory. The user can also unset the HISTFILE variable to disable the history saving feature. For example, the following command will unset the HISTFILE variable:

unset HISTFILE

This will prevent the history from being written to any file when the Bash process exits. The user can view the value of the HISTFILE variable by using the echo command. For example, the following command will display the value of the HISTFILE variable:

echo $HISTFILE

The output will be something like:

/home/user/.bash_history

∗∗Thegrepcommandthatwillprintonlythelinesthatdonotendwitha/inthefilefooisgrep−v′/’ foo. This command uses the following options and pattern:

-v: Inverts the matching, meaning that it only outputs the lines that do not match the pattern. /:Matchesa/characterattheendofaline.The symbol represents the end of a line in regular expressions. foo: The name of the file to search.

The output of this command will show all the lines in the file foo that do not have a / as the last character. For example, if the file foo contains the following lines:

/home/user/ /var/log/messages /etc/passwd /usr/bin/

The output of the command will be:

/var/log/messages /etc/passwd

The other commands are incorrect for the following reasons:

grep ‘/$’ foo: This command will print only the lines that do end with a / in the file foo, which is the opposite of what is required.

grep ‘/#’ foo: This command will print only the lines that contain the string /# in the file foo, which is not related to the question.

grep -v ‘/#’ foo: This command will print only the lines that do not contain the string /# in the file foo, which is also not related to the question.