LPI Updated 101-500 Exam Questions and Answers by jac

The + symbol in a grep regular expression means to match the preceding character or character set one or more times. In other words, it means to repeat the previous element at least once. For example, the regular expression ^d[aei]\+d$ will match any word that starts and ends with d and has one or more of the letters a, e or i in between. Some examples of words that match this pattern are dead, deed, died, daiid, etc. The other options are either incorrect or not applicable. The * symbol means to match the preceding character or character set zero or more times. The ? symbol means to match the preceding character or character set zero or one times. The \+ symbol means to match a literal + symbol, not a repetition modifier. 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 <, > and %> are valid stream redirection operators within Bash. The < operator redirects the standard input of a command from a file or another command. For example, sort < names.txt will sort the lines of the file names.txt and print them to the standard output. The > operator redirects the standard output of a command to a file or another command, overwriting the file if it exists. For example, echo "Hello World" > greeting.txt will write the string “Hello World” to the file greeting.txt. The %> operator redirects the standard error of a command to a file or another command, overwriting the file if it exists. For example, ls foo %> errors.log will list the contents of the directory foo and write any error messages to the file errors.log. The other options are either invalid or do not perform the desired task. The <<< operator is not a valid Bash operator, but it is used in some other shells like Zsh to redirect a string literal as the standard input of a command. The >>> operator is not a valid Bash operator, but it is used in some programming languages like Python to denote a bitwise right shift operation. References:

LPIC-1 Exam 101 Objectives, Topic 103: GNU and Unix Commands, 103.4 Use streams, pipes and redirects

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

 The command foo 1> bar redirects the standard output (stdout) from the command foo to the file bar, overwriting the existing contents of the file. The number 1 before the redirection operator > indicates the file descriptor of the stdout stream, which is 1 by default. The redirection operator > means that the output of the command is written to the file, replacing any previous data in the file. The file name after the redirection operator is the destination of the output. For example, if the command foo prints “Hello world” to the stdout, and the file bar contains “Goodbye world”, the command foo 1> bar will write “Hello world” to the file bar, erasing “Goodbye world”. The other options are not correct because:

A. The stdout from the command foo is appended to the file bar: This is not what 1> does, because it overwrites the file, not appends to it. To append the output to the file, the operator >> should be used instead of >.

C. The command foo receives its stdin from the file bar: This is not what 1> does, because it redirects the output, not the input. To redirect the input from the file, the operator < should be used instead of >.

D. The command foo receives its stdin from the stdout of the command bar: This is not what 1> does, because it redirects the output to a file, not to another command. To redirect the output to another command, the operator | (pipe) should be used instead of >.

E. The stderr from the command foo is saved to the file bar: This is not what 1> does, because it redirects the stdout, not the stderr. To redirect the stderr, the file descriptor 2 should be used instead of 1.

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.