Linux basic shell scripting questions

Basic shell scripting questions

1.        How do you find out what’s your shell? - echo $SHELL

2.       What’s the command to find out today’s date? - date

3.       What’s the command to find out users on the system? - who

4.       How do you find out the current directory you’re in? - pwd

5.        How do you remove a file? - rm

6.       How do you remove a <="" b="">- rm -rf

7.       How do you find out your own username? - who am i

8.      How do you send a mail message to somebody? - mailsomebody@techinterviews.com -s ‘Your subject’ -c ‘cc@techinterviews.com‘

9.      How do you count words, lines and characters in a file? - wc

10.   How do you search for a string inside a given file? - grep string filename

11.    How do you search for a string inside a directory? - grep string *

12.   How do you search for a string in a directory with the subdirectories recursed? - grep -r string *

13.   What are PIDs? - They are process IDs given to processes. A PID can vary from 0 to 65535.

14.   How do you list currently running process? - ps

15.    How do you stop a process? - kill pid

16.   How do you find out about all running processes? - ps -ag

17.    How do you stop all the processes, except the shell window? - kill 0

18.   How do you fire a process in the background? - ./process-name &

19.   How do you refer to the arguments passed to a shell script? - $1, $2 and so on. $0 is your script name.

20.  What’s the conditional statement in shell scripting? - if {condition} then … fi

21.   How do you do number comparison in shell scripts? - -eq, -ne, -lt, -le, -gt, -ge

22.  How do you test for file properties in shell scripts? - -s filename tells you if the file is not empty, -f filename tells you whether the argument is a file, and not a directory, -d filename tests if the argument is a directory, and not a file, -w filename tests for writeability, -r filename tests for readability, -x filename tests for executability

23.  How do you do Boolean logic operators in shell scripting? - ! tests for logical not, -a tests for logical and, and -o tests for logical or.

24.  How do you find out the number of arguments passed to the shell script? - $#

25.   What’s a way to do multilevel if-else’s in shell scripting? - if {condition} then {statement} elif {condition} {statement} fi

26.  How do you write a for loop in shell? - for {variable name} in {list} do {statement} done

27.   How do you write a while loop in shell? - while {condition} do {statement} done

28.  How does a case statement look in shell scripts? - case {variable} in {possible-value-1}) {statement};; {possible-value-2}) {statement};; esac

29.  How do you read keyboard input in shell scripts? - read {variable-name}

30.  How do you define a function in a shell script? - function-name() { #some code here return }

31.   How does getopts command work? - The parameters to your script can be passed as -n 15 -x 20. Inside the script, you can iterate through the getopts array as while getopts n:x option, and the variable $option contains the value of the entered option.