Bash - Unix Shell/Linux CLI

Question 1

What is an exit status (message/number) in Bash? $?

Answer 1

An exit status is a numeric code a command returns after execution ($?), where 0 means success and any non-zero value indicates an error or failure.

So if you: echo $?
Output: 234
Then the last command you ran failed with an error code: 234.

Question 2

What does grep do?

Answer 2

grep searches for a given string and outputs all those X that contains the given string “ “.

Question 3

What does this command show: tail -n 10 /var/log/syslog ?

Answer 3

Shows the last 10 lines of the file /var/log/syslog — in your terminal.

Question 4

What’s the difference between > and&raquo_space; in Bash?

Answer 4

> redirects output to a file, overwriting existing content and creating a new file if not in existence already.
> appends output to the end of a file without overwriting it’s contents.

So: echo “overwritten” > fileOld.txt
Will overwrite/replace all fileOld.txt content with “overwritten”.

Question 5

What does the env or printenv command do in Bash?

Answer 5

env = displays current environment variables.

Question 6

What is fi in Bash?

Answer 6

fi is the keyword that closes an if statement block in Bash scripting, marking the end of the conditional.

Question 7

What is done in Bash?

Answer 7

done marks the end of a loop block (such as for, while, or until) in Bash scripting.

Question 8

What is do in Bash?

Answer 8

do marks the beginning of the commands to execute inside a loop (for, while, or until) in Bash scripting.

Question 9

What is df in Bash?

Answer 9

df (disk free) is a command that displays the amount of disk space used and available on mounted filesystems.