Automation with Bash: Cron Jobs, Shell Scripts, and Pipelines Quiz Quiz

Explore essential Bash automation skills with this quiz covering cron syntax, shell scripting basics, and the use of pipelines. Enhance your knowledge of scheduling tasks, automating repetitive processes, and connecting commands efficiently in Unix-like systems.

1. Understanding Cron Syntax

   Which cron schedule will execute a script every day at 2:30 AM?

   1. 30 2 * * *
   2. * * 2 30 *
   3. 2 30 * * *
   4. 0 30 2 * *

   Explanation: The correct answer is '30 2 * * *', which translates to 2:30 AM every day. The first field is minutes (30), followed by hour (2), day of month (*), month (*), and day of week (*). '2 30 * * *' would attempt to run at 30 AM on hour 2, which is invalid. '* * 2 30 *' is not a valid cron structure, and '0 30 2 * *' mixes up the fields. Understanding the field order is crucial for correct scheduling.

2. Executable Permissions

   Before running a shell script directly by name, which command must you use to ensure it can be executed?

   1. exec script.sh
   2. chmod +x script.sh
   3. make script.sh
   4. shmod script.sh

   Explanation: Setting executable permission with 'chmod +x script.sh' is necessary to run the script directly. 'exec script.sh' is used to replace the shell with the script but only works if the script is already executable. 'make script.sh' is a build system command, not for permissions, and 'shmod script.sh' is a common typo or incorrect command. Proper permissions are essential for running scripts securely and effectively.

3. Function of the Shebang Line

   What is the main purpose of the shebang (e.g., #!/bin/bash) at the top of a shell script?

   1. It tells the system which interpreter to use when running the script.
   2. It provides a comment for the script user.
   3. It defines environment variables for the script.
   4. It declares the filename of the script.

   Explanation: The shebang line indicates the interpreter (such as /bin/bash) to use for running the script. It is not simply a comment, though marked with '#', and does not declare the filename or set environment variables. Properly specifying the interpreter ensures the script runs as intended across different environments.

4. Basic Cron Editing Command

   Which command should you enter to edit your current user's scheduled cron tasks?

   1. crontab -e
   2. cronedit
   3. edit-cron
   4. cron -c

   Explanation: 'crontab -e' opens the cron table editor for the current user, allowing task scheduling. 'cronedit' and 'edit-cron' are not standard system commands, and 'cron -c' is invalid syntax. Using the right command is essential for proper task management.

5. Connecting Commands with Pipelines

   In Bash, which symbol is used to connect two commands so that the output of the first becomes the input of the second?

   1. ;
   2. |
   3. u0026
   4. u003E

   Explanation: The pipe symbol '|' connects commands, passing output from the left to input on the right. 'u0026' puts a command in background, ';' separates commands to run sequentially, and 'u003E' redirects output to a file. Piping enables powerful data manipulation within scripts and the shell.

6. Cron Time Fields

   In a cron schedule '0 6 * * 1', on which days will the job run?

   1. Every Sunday
   2. First day of the month
   3. Every Monday
   4. Every day at 6 AM

   Explanation: In cron, the fifth field selects the day of the week. '1' corresponds to Monday, so '0 6 * * 1' runs at 6:00 AM every Monday. 'Every Sunday' would require a '0' or '7' in that position. 'Every day at 6 AM' would be '0 6 * * *', and the first day of the month would have a '1' in the third field.

7. Scheduling Frequency with Cron

   Which cron entry would run a backup script.sh every 10 minutes?

   1. */10 * * * * script.sh
   2. */1 10 * * * script.sh
   3. * 10 * * * script.sh
   4. 10 * * * * script.sh

   Explanation: '*/10 * * * *' means every 10 minutes past the hour. '* 10 * * *' runs at every minute, but only during the tenth hour. '10 * * * *' schedules only at minute 10 of any hour, not every 10 minutes. '*/1 10 * * *' would run every minute during hour 10. Frequency relies on proper field understanding.

8. Variables in Bash Scripts

   Which line correctly assigns the value 'hello' to a variable named GREETING in a Bash script?

   1. GREETING == 'hello'
   2. GREETING:'hello'
   3. GREETING='hello'
   4. GREETING=hello

   Explanation: Variable assignment in Bash is done using the '=' sign without spaces and quotes around strings, making 'GREETING='hello'' accurate. 'GREETING=hello' is valid, but if 'hello' contains spaces, it will break. 'GREETING:'hello'' and 'GREETING == 'hello'' are invalid Bash syntax for variable assignment.

9. Viewing Cron Job Lists

   Which command lists the cron jobs scheduled for the current user?

   1. crontab -l
   2. cronlist
   3. listcrontab
   4. lscron

   Explanation: 'crontab -l' displays the cron table for the current user. 'lscron', 'cronlist', and 'listcrontab' are not default commands on Unix-like systems. Correctly listing scheduled jobs is essential for cron management and troubleshooting.

10. Purpose of the Exit Status in a Script

    Why might a Bash script use the command 'exit 1' at the end of its execution?

    1. To restart the script automatically.
    2. To pause the script indefinitely.
    3. To signal an error or abnormal termination to the calling process.
    4. To log a message successfully.

    Explanation: An exit status of '1' indicates that a script completed with an error, which can be caught by other processes or automation tools. It does not log messages, pause execution, or cause automatic restarts. Using exit codes properly helps other scripts or users identify whether the script succeeded or failed.