LPI 102 - Shells, Scripting And Data Management 2- Marcus Vinicius Braga Alcantara

The statement is true. The "alias" command allows users to create aliases for commands in the system, which means they can create shortcuts or alternative names for commands. On the other hand, the "unalias" command is used to remove aliases from the system. So, the "alias" command creates aliases, while the "unalias" command removes them. Therefore, the statement is correct.

When closing the shell, the bash executes the instructions contained in the file ~/.bash_logout, if it exists.

An alias provides the benefit of avoiding the need to type long commands. By creating a shorter alias for a command, users can save time and effort by simply using the alias instead of typing out the entire command. This can be particularly useful for frequently used or complex commands, as it allows for quicker and more efficient execution.

The given correct answer states that the command "echo "eu sou o usuário: $USER"" will return the text "eu sou o usuário:" followed by the name of the current user. This is because "$USER" is a special variable that holds the name of the current user in Unix-like operating systems. Therefore, when the command is executed, it will replace "$USER" with the actual username and display the complete sentence.

The correct answer is /etc/skel or /etc/skel/. The directory /etc/skel is used to keep a sample copy of files and directories that will be automatically copied to a new user's home directory when it is created. This allows the new user to have a pre-defined set of files and directories already in place.

The correct answer is /etc/skel or /etc/skel/. When creating a new user account using the useradd command with the -m option, the content of the /etc/skel directory will be copied to the new user's home directory. The /etc/skel directory contains default files and configurations that will be available to the new user upon account creation.

To display an application on another computer's screen, you need to set or edit the "DISPLAY" environment variable. This variable specifies the display server's address where the application should be shown. By setting the "DISPLAY" variable to the appropriate value (e.g., IP address or hostname of the remote computer), the application will be able to appear on the desired screen.

The given SQL instruction is missing the keyword "SELECT" before the count(*) function. In SQL, the SELECT keyword is used to retrieve data from a database table, and it should be included before the count(*) function to specify which columns or data we want to retrieve.

The missing word to complete the conditional statement in bash is "fi". In bash scripting, "fi" is used to close the "if" statement. It indicates the end of the block of code that should be executed if the condition specified in the "if" statement is true.

The correct answer is "unset". This command is used to remove or unset a variable from the environment. In this case, the variable "CFLAGS" is being removed from the environment by using the "unset" command.

The missing word in the SQL instruction is "from". The "from" keyword is used to specify the table from which the data is being selected in the SQL query.

The correct answer is "grant e revoque". In SQL, the "grant" command is used to apply rights and permissions to database objects, allowing users to perform certain actions on them. On the other hand, the "revoque" command is used to revoke or remove those rights and permissions from users. So, these two commands are used to grant and revoke rights and restrictions in the standard SQL language.

The given shell script will return the value "O resultado é: 30".

The missing keyword in this shell script example is "for". It is used to create a loop that will iterate a specific number of times, based on a given condition or range of values. The "for" loop is commonly used when you know the exact number of iterations you want to perform.

The given statement is true. The explanation states that there is a problem when performing mathematical operations with the bash shell because its operators only support arithmetic with integers. It provides an example of a shell script that performs a division operation, where the correct value to be returned would be 4.5, but the bash shell will return the integer value of 4 instead. The explanation suggests using the internal calculator of bash (bc) as an alternative solution to this problem.

The correct answer is to create a function. By creating a function, you can define a series of commands that can be easily executed whenever needed. This allows you to have the series of commands available in your login and execute them in the current shell.

The command "seq 10" will produce the numbers from 1 to 10, with each number on a separate line.

The correct answer is ~/.bashrc and ~/.bash_profile. These two files affect the behavior of the Bash shell. The ~/.bashrc file contains the individual user configurations for the Bash shell, such as aliases, functions, and settings. It is executed for each new interactive shell session. On the other hand, the ~/.bash_profile file is executed only for login shells and is commonly used to set environment variables and execute commands that should be run once when the user logs in.

The correct answer explains that both options (-e and -f) check for the existence of the path. However, the -f option also confirms that the path is a regular file.

This command will update the PATH variable by adding the value of $APPLICATIONS to it. The $PATH represents the current value of the PATH variable, and the $APPLICATIONS represents the value of the APPLICATIONS variable. By using the command "export PATH=$PATH:$APPLICATIONS", the PATH variable will be updated to include the value of $APPLICATIONS, allowing the system to search for executables in that directory.

The brackets "[ ]" used after the if statement can be replaced by the command "test". This means that the condition being tested in the if statement is being evaluated using the "test" command.

When we log in to a Linux system, the bash shell is started with a login shell. This shell looks for four initialization files to process its commands in the following order: /etc/profile, ~/.bash_profile, ~/.bash_login, and ~/.profile. The answer provided lists the correct order of these files for the shell to process.

When the command "echo $?" returns an output equal to 1, it indicates that the command executed immediately before the echo command had an exit status of 1. The exit status is a value returned by a command to the shell, indicating whether the command executed successfully or encountered an error. Therefore, in this case, the correct answer is that it is the exit value of the command executed immediately before the echo command.

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JOIN is the correct answer because it is the command used in SQL to combine the result of a query from two different tables based on a common relationship between them. It allows for the retrieval of data from multiple tables in a single query by matching rows with the same values in specified columns. This helps in creating a connection between related data and obtaining a comprehensive result set.

The correct answer is ".bashrc". This file is a script that is executed whenever a new interactive shell is started. By editing this file, the user can customize their shell environment, including setting the default editor for programs started from the home directory.

The correct answer is "ls *.mp3" because this command will list all files in the current directory that have the .mp3 extension, which is the same output as the given script.

The given question is asking for the instruction that executes an action in a loop until a condition is no longer true. The correct answer is "while" because the "while" loop continues to execute the code block as long as the specified condition is true. Once the condition becomes false, the loop stops executing.

The correct answer is = and -eq. These are operators used in the test command for comparisons. The = operator is used for string comparisons, while the -eq operator is used for numeric comparisons.

A opção correta é "select count(*) from tbl_Livro;". Essa consulta irá retornar a quantidade de registros na tabela "tbl_Livro". O comando "count(*)" conta o número de linhas na tabela. As outras opções não retornarão a quantidade de registros, mas sim outros tipos de informações, como todos os registros da tabela ("select * from tbl_Livro;"), o valor máximo de uma coluna ("select max(*) from tbl_Livro;") e a média de uma coluna ("select avg(*) from tbl_Livro;").

The "set" command is the best way to list all the shell variables defined. It displays all the variables, including environment variables, local variables, and shell functions. The "env" command lists only the environment variables, while "env -a" lists all variables, including environment variables and shell variables, but it is not the best option as it includes unnecessary information. The "echo $ENV" command only displays the value of the "ENV" environment variable, not all variables.

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The correct answer is "/etc/bash.bashrc e /etc/profile". In Bash, the "/etc/bash.bashrc" file is used for "interactive" shells, while the "/etc/profile" file is used for "login" shells. These files contain initialization scripts that are executed when a shell is started, providing settings and configurations for the shell environment.

After defining the function "myfunction { echo $1 $2; }" in the bash, the output on stdout when executing "myfunction A B C" will be "A B". This is because the function is defined to only echo the first two arguments passed to it, which in this case are "A" and "B". The third argument "C" is not included in the output.

The correct answer is "O comando deve está entre crases. Ex: PROCESSOS_ATUAIS=`ps aux`". This is because using backticks or crases around a command in shell scripting allows the output of that command to be assigned to a variable. In this case, the command "ps aux" will be executed and the output will be stored in the variable PROCESSOS_ATUAIS.

To rename a table in SQL, the correct syntax is "rename table Clientes to Meus_Clientes;". This statement will change the name of the table "Clientes" to "Meus_Clientes".

The correct answer is "drop user smith". In SQL, the "drop user" command is used to remove a user from the database. By specifying the username "smith" after the command, it indicates that the user named "smith" should be removed. The other options ("delete user smith", "cancel user smith", and "remove user smith") are not valid SQL commands for removing a user.

The correct answer is mydate="$(date)". This command assigns the output of the "date" command to the shell variable called "mydate". The "$()" syntax is used to capture the output of a command and assign it to a variable.

The correct answer states that the order of the fields is not important when inserting data into the table, as long as the order of the values matches the order of the fields. This means that when inserting data, the values must be provided in the same order as the fields in the table, but the fields themselves can be in any order.

The correct answer is "function sumitup { echo $(($1 + $2)) ; }". This is the correct command to create a Bash function that generates the sum of two numbers. The function is named "sumitup" and it uses the echo command to output the result of the addition of the two input numbers, which are represented by $1 and $2. The $(()) syntax is used to perform the arithmetic addition operation.

Os usuários geralmente querem configurar seu login e shell interativo de maneira similar. Para fazer isso, eles escolhem interpretar (ou "fonte") o conteúdo de ~/.bashrc no arquivo ~/.bash_profile. É possível fazer a mesma coisa com arquivos comuns a todos os usuários referenciando /etc/bash.bashrc a partir de /etc/profile.

The correct answer is "RESULT=$[2+6], RESULT=$((2+6))". The first option "RESULT=$[2+6]" uses the square brackets syntax to perform the mathematical operation and assign the result to the variable RESULT. The second option "RESULT=$((2+6))" uses double parentheses to perform the mathematical operation and assign the result to the variable RESULT.

The given answer suggests using the backslash (\) before the command "ls" to execute the original version of the command. In this case, the backslash will bypass any alias that may have been set for the "ls" command and directly execute the original command.

The correct answer is "AND, OR e AND NOT". In SQL, the logical operators "AND" and "OR" are used to combine multiple conditions in a query, while "AND NOT" is used to exclude certain conditions from the result set. The other options listed do not contain valid SQL logical operators.

To temporarily remove the environment variable FOOBAR in order to test a shell script called meuscript, the command "env -u FOOBAR meuscript" can be used. This command unsets the value of the FOOBAR variable for the duration of executing the meuscript script.

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The instruction "until" executes an action in a loop until a certain condition becomes true.

The given command "echo '1 2 3 4 5 6' | while read a b c ; do echo resultado: $c $b $a; done" reads the input "1 2 3 4 5 6" and assigns the values to variables a, b, and c. Then, it echoes the result in the format "resultado: $c $b $a". So, the output will be "resultado: 3 4 5 6 2 1".

The "declare -f" and "typeset -f" commands are used to display only the available functions in a bash shell. The "set" command displays all shell variables and functions, not just the functions. The "function" command is not a valid command in bash. Therefore, the correct answers are "declare -f" and "typeset -f".

When bash is initialized in an interactive shell session (excluding an X session), it looks for instructions from the files /etc/bash.bashrc and ~/.bashrc if they exist. The /etc/bash.bashrc file contains system-wide bash initialization instructions, while the ~/.bashrc file contains user-specific bash initialization instructions. By checking these files, bash can execute any commands or configurations specified in them to set up the shell environment correctly for the user.