Shell script : Interview Questions

Q. What is the output if execute ./temp.sh

temp.sh

#!/bin/bash

./temp1.sh

echo Hello

temp1.sh

#!/bin/bash

exit 1

Answer.

Exit from temp1.sh will lead to exit from script and print nothing.

Q. What is difference between : 

a) echo "Good      morning"

b) echo Good      morning

Answer.

Double quotes print spaces (in between) while without double quote will print a single space instead of many spaces.

Q. exit -1 vs. exit 1

Answer. When exit command returns any value other than 0 (zero), the script will throw an error and will abort.

0 (zero) represents successful execution.

exit -1 or exit 1 (without quotes) before script termination will abort the script.

Q. How to remove first line (header) from a file ?

Answer.  # sed '1 d' file.txt

Q. How to check if a file or directory exists or not ?

Answer.

if [ -f $myfile ]

then

   echo "$myfile exists"

fi

Flag -d checks the directory exists or not.

Q. If I try to un mount a file system it say’s resource is busy.

# umount /mnt/dir

How you check what is the problem ?

(Here, ps command is giving no clue to you)

Answer.

1. Try fuser which will tell you which processes are accessing the mount point.

# fuser -vm /mnt/dir

Then, you can use ps command to find the process

2. Try lsof command which shows each open file on the mount.

# lsof /mnt/dir

# lsof | grep '/mnt/dir'

Q. How to display the shell's environment variables ?

$ env

Q. How to start running a process in background ?

$ ./process-name &

Q. How to find out the number of arguments passed to the shell script ?

Use ?#

Q. How to refer to the arguments passed to a shell script ?

Use $0 for script name

Use $1, $2, $3 .... $n  for arguments passed to script