Wednesday, June 27, 2012

Basic shell scripting part 2

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

What’s a way to do multilevel if-else’s in shell scripting?
Answer: if then elif fi
How do you write a for loop in shell?
Answer: for in do done
How do you write a while loop in shell?
Answer: while do done
How does a case statement look in shell scripts?
Answer: case in ) ;; ) ;; esac
How do you define a function in a shell script?
Answer: function-name()
How do you find out about all running processes?
Answer: ps -ag
How do you stop a process?
Answer: kill pid
How do you remove a file?
Answer: rm
How do you remove recursively?
Answer: rm -rf
What are PIDs?
Answer: They are process IDs given to processes. A PID can vary...
How do you list currently running process?
Answer: ps
What is $$?
What is a named pipe?
What does || mean?
What does && mean?
What is a loop?
What does while do?
What is a function? 
What are the different kinds of loops available in shell script?
for if while case

What does $# stand for?
$# returns the number of parameters that are passed to a shell script
$? returns the exit code of the last executed command (0 : Successful, 1 or other: Failed)
What does $? return?
Will return the status of the command which is executed lastly.
0 > Success
2 > Error
How do u open a read only file in Unix?
"vi -R filename"
What is the difference between a shell variable that is exported and the one that is not exported?
If you have a string "one two three", Which shell command would you use to extract the strings?
How do you schedule a command to run at 4:00 every morning?
How will you list only the empty lines in a file (using grep)?
grep ^$ filename.txt
When you login to a c shell, which script would be run first? (before the terminal is ready for the user)
first /etc/.login script is run & after that
~/.login is run & then ~/.cshrc is run.
How would you get the character positions 10-20 from a text file?
cat filename.txt | cut -c 10-20
How would you print just the 25th line in a file (smallest possible script please)?
tail -n +25Â | head -1 OR
head -n 25 | tail -1
How would you replace the n character in a file with some xyz?
sed 's/n/xyz/g' filename > new_filename