Unix Shell Scripting Interview Questions - 1

• How do you find out what’s your shell? - echo $SHELL
• What’s the command to find out today’s date? - date
• What’s the command to find out users on the system? - who
• How do you find out the current directory you’re in? - pwd
• How do you remove a file? - rm
• How do you remove a - rm -rf
• How do you find out your own username? - whoami
• How do you send a mail message to somebody? - mail somebody@mindgrillq.com -s ‘Your subject’ -c ‘cc@mindgrillq.com‘
• How do you count words, lines and characters in a file? - wc
• How do you search for a string inside a given file? - grep string filename
• How do you search for a string inside a directory? - grep string *
• How do you search for a string in a directory with the subdirectories recursed? - grep -r string *
• What are PIDs? - They are process IDs given to processes. A PID can vary from 0 to 65535.
• How do you list currently running process? - ps
• How do you stop a process? - kill pid
• How do you find out about all running processes? - ps -ag
• How do you stop all the processes, except the shell window? - kill 0
• How do you fire a process in the background? - ./process-name &
• How do you refer to the arguments passed to a shell script? - $1, $2 and so on. $0 is your script name.
• What’s the conditional statement in shell scripting? - if {condition} then … fi
• How do you do number comparison in shell scripts? - -eq, -ne, -lt, -le, -gt, -ge
• 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
• 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.
• How do you find out the number of arguments passed to the shell script? - $#
• What’s a way to do multilevel if-else’s in shell scripting?
  - if {condition} then {statement} elif {condition} {statement} fi
• How do you write a for loop in shell? - for {variable name} in {list} do {statement} done
• How do you write a while loop in shell? - while {condition} do {statement} done
• How does a case statement look in shell scripts?
  - case {variable} in {possible-value-1}) {statement};; {possible-value-2}) {statement};; esac
• How do you read keyboard input in shell scripts? - read {variable-name}
• How do you define a function in a shell script? - function-name() { #some code here return }
• 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.