20250413

Question 1

What does file?.sh match?

Answer 1

Files named file + 1 character + .sh (e.g., file1.sh, fileA.sh)

The ? wildcard matches exactly one character.

Question 2

What does [abc]*.csv match?

Answer 2

Files starting with a, b, or c and ending in .csv (e.g., a_data.csv, c123.csv)

The brackets [] specify a set of characters.

Question 3

What does [!x]* match?

Answer 3

Files that do not start with x (e.g., apple, test, but not xray)

The ! inside brackets negates the character set.

Question 4

What does ???.log match?

Answer 4

Files with exactly 3 characters before .log (e.g., app.log, xyz.log)

The ? wildcard matches exactly one character.

Question 5

What is the option in ls command to make it recursive?

Answer 5

-R

Question 6

What does echo {bubble,quick,merge}sort.java return?

Answer 6

bubblesort.java quicksort.java mergesort.java

Question 7

How to return file3 file4 file5 file6 file7 file8 file9 file10 file11 in Linux ?

Answer 7

echo file{3..15}

Question 8

$LOGNAME

Answer 8

your login name, like fashouri

Question 9

How to return your shell’s previous directory, prior to the last cd command?

Answer 9

$OLDPWD

Question 10

What does $PATH return?

Answer 10

Your shell search path

Question 11

What is the definition of $USER in Linux?

Answer 11

$USER: Current effective user (from shell environment)

Represents the name of the user currently logged into the shell session.

Question 12

What does $LOGNAME represent in Linux?

Answer 12

$LOGNAME: Original login name (from system login)

This variable reflects the user’s name as it was set at login.

Question 13

How do $USER and $LOGNAME typically compare?

Answer 13

They’re usually the same, but can differ after sudo or su

$USER may change when switching users with sudo or su, while $LOGNAME remains constant.

Question 14

What is an environment variable?

Answer 14

A key-value pair used by the operating system to configure behavior for processes.

Question 15

How do you list all environment variables in Linux?

Answer 15

printenv

Question 16

How do you view a specific environment variable, e.g., HOME?

Answer 16

echo $HOME

Question 17

How do you temporarily set an environment variable in Linux?

Answer 17

export VAR_NAME='value'

Question 18

How do you make an environment variable permanent?

Answer 18

Add export VAR_NAME='value' to ~/.bashrc or ~/.zshrc and run source ~/.bashrc or source ~/.zshrc.

Question 19

Where are permanent environment variables commonly set for Bash?

Answer 19

~/.bashrc or ~/.bash_profile

Question 20

Does export VAR_NAME=value persist after you close the terminal?

Answer 20

No, it’s only temporary for that session.

Question 21

What does the PATH environment variable do?

Answer 21

Specifies directories where executable programs are located.

Question 22

How do you remove an environment variable for the current session?

Answer 22

unset VAR_NAME

Question 23

What is the command to reload a shell configuration file after editing it?

Answer 23

source ~/.bashrc (or the appropriate file like ~/.zshrc)

Question 24

What happens when you run cat < file.txt?

Answer 24

The contents of file.txt are passed into stdin of cat

Question 25

How do you redirect only `stderr` to a file in Linux?

Answer 25

Use `2>` (e.g., `command 2> error.txt`)

Question 26

How do you combine `stdout` and `stderr` into the same file?

Answer 26

`command &> output.txt`

Question 27

What does the command `ls not_a_file 2> error.txt` do?

Answer 27

Redirects the error message (stderr) to `error.txt`

Question 28

How do you redirect only `stdout` to a file in Linux?

Answer 28

Use `>` or `1>` (e.g., `command > output.txt`)

Question 29

How do you append both stdout and stderr to the same file in Linux?

Answer 29

`command &>> file.txt` — this appends both outputs to file.txt correctly.

Question 30

How to append stderr to a file?

Answer 30

`command 2>> file.txt`