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Wednesday, August 17, 2016

Top 20 Shell Scripting Interview Questions And Answers.

Top 20 Shell Scripting Interview Questions And Answers. Latest Shell Scripting Interview Questions For Freshers And Experienced. Most Frequently Asked Shell Scripting Interview Questions.

1: I want to monitor a continuously updating log file, what command can be used to most efficiently achieve this?

We can use tail –f filename     . This will cause only the default last 10 lines to be displayed on std o/p which continuously shows  the updating part of the file.

2: I want to connect to a remote server and execute some commands, how can I achieve this?

We can use telnet to do this:

telnet hostname –l user

>Enter password

>Write the command to execute

>quit

3: I have  files and I want to print the records which are common to both.

We can use “comm” command as follows:

comm -1 file1 file               … 1 will suppress the content which are

unique to 1st and nd  file respectively.

4: Write a script to print the first 10 elemenst of Fibonacci series.


#!/bin/sh

a=1

b=1

echo $a

echo $b

for I in 1  3 4 5 6 7 8

do

c=a

b=$a

b=$(($a+$c))

echo $b

done

5: How will you connect to a database server from linux?

We can use isql utility that comes with open client driver  as follows:

isql –S serverName –U username –P password

6: What are the 3 standard streams in Linux?

0 – Standard Input
1 – Standard Output
 – Standard Error

7: I want to read all input to the command from file1 direct all output to file and error to file 3, how can I achieve this?

command <file1 1>file >file3

8: What will happen to my current process when I execute a command using exec?

“exec” overlays the newly forked process on the current  process ; so when I execute the command using exec, the command gets executed on the current shell without creating any new processes.

Eg: Executing “exec  ls”  on command prompt will execute ls and once ls exits, the process will shut down

9: How will you emulate wc –l using awk?

awk ‘END {print NR} fileName’

10: Given a file find the count of lines containing word “ABC”.

grep –c  “ABC” file1

11: How will you find the 99th line of a file using only tail and head command?

tail +99 file1|head -1

12: Print the 10th line without using tail and head command.


sed –n ‘10p’ file1 

13:In my bash shell I want my prompt to be of format  ‘$”Present working directory”:”hostname”>  and load a file containing a list of user defined functions as soon as I login , how will you automate this?

In bash shell we can create “.profile”  file which automatically gets invoked as soon as I login and write the following syntax into it.


export PS1=’$ `pwd`:`hostname`>’ .File1

Here File1 is the file containing the user defined functions and “.” invokes this file in current shell.

14: Explain about “s” permission bit in a file?

“s” bit is called “set user id” (SUID) bit.

“s” bit on a file causes the process to have the privileges of the owner of the file during the instance of the program.

Eg: Executing “passwd” command to change current password causes the user to writes its new password to shadow file even though it has “root” as its owner.

15: I want to create a directory such that anyone in the group can create a file and access any person’s file in it but none should be able to delete a file other than the one created by himself.

We can create the directory giving read and execute access to everyone in the group and setting its sticky bit “t” on as follows:


mkdir direc1

chmod g+wx direc1

chmod +t direc1

16: How can you find out how long the system has been running?

Command “uptime”

17: How can any user find out all information about a specific user like his default shell, real life name, default directory,when and how long he has been using the sytem?

finger  “loginName”                  …where loginName is the  login name of  the

user whose  information is expected.

18: What is the difference between $$ and $!?

$$ gives the process id of the currently executing process whereas $! shows the process id of the process that recently went into background.

19: What are zombie processes?

These are the processes which have died but whose exit status is still not picked by the parent process. These processes even if not functional still have its process id entry in the process table.

20: How will you copy file from one machine to other?

We can use utilities like “ftp” ,”scp” or “rsync” to copy file from one machine to other.

Eg: Using ftp:

ftp hostname

>put file1

>bye

Above copies file file1 from local system to destination system whose hostname is specified.

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