Interview Questions
Reference: https://www.youtube.com/watch?v=6ue2luv2I-Y&t=65s
How to find the no of arguments passed
$# –> will give the no of arguments passed while invoking the shellscript
How to get the name of the shell script file inside the script
$0 will give the script name
###How to know whether last command is executed successfully $? –> will return the status code of the last command executed
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How to get the last line from the file tail -1 file_name (By default tail file_name will return last 10 lines of file, if we pass -3 it will show the last three lines)
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How to get the first line from the file head -1 file_name (By default tail file_name will return first 10 lines of file, if we pass -3 it will show the first 3 lines)
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How to get third element from each line awk ‘{print $3}’ filename ps -aux | awk ‘{print $3}’
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How to write a function in shell script #!/bin/sh
Define your function here
Hello () { echo “Hello World $1 $2” return 10 }
Invoke your function
Hello Zara Ali
Capture value returnd by last command
ret=$? # For function it will return return_value, for others it will return status code echo “Return value is $ret”
Intermediate:
- The history command cnnot be executed from bash shell script, but it will work in c shell
9.How would you compare the strings in script The test command is used to compare the text strings. The text command compares text strings by comparing each character in each string
10 How to redirect both the standard output and standard error to the same location command1 > out.txt 2> err.txt
11 what are the default permisions of the file when it is created -rw-r–r– 1
12 Determine the output of the command echo ${new:-variable} output: variable Here new is the variable name, if this variable name is already defined, it will take that value, else it will pass this default value “variablbe” to the variable name “new”
13.How to get part of the string with echo command only echo ${variable_name:2:6} where 2 is the staring index and 6 is the count of characters after the starting index
14 Rewrite the commamd to print the sentence and convert the variable to plurla variable=”plane”; echo “I like ${variable}s” output: I like planes
15 To print the first array element #!/bin/bash array={“Hi”, “my”, “name”, “is”, “vignesh”} echo ${array[0]}
16 To print all elements of array and its index echo ${array[@]} – >Printing all array elements echo ${!array[@]} –> printing array index
Experienced 17 what is crontab The crontab is a list of commands that you want to run on a regular schedule and also the name of the command used to manage the list. –> Crontab stand for “cron table” because it uses the job schediler cron to execute the tasks –> The schedule is called the crontab, which is also the name of the program used to edit that schedule.
18 How many fields are present in a crontab file and what does each feild specify? The crontab file has fix fields, –> The first five feilds tell cron when to execute the command : minute(0-59), hour(0-23, day(1-31),) month(1-12), and the day of the week (0-6) 0-sunday –> The sixth field contains the command to be executed
19 what are the two files of crontab command ? –> cron.allow - It decides which users need to be permitted from using the crontab command –> cron.deny - It decides which users need to be prevented from using the crontab command Redhat/centos –> /var/spool/cron directory DEbian/ubuntu –> /cron/crontab directory
20 what command needs to be used to take the backup? tar –> tape archive tar -czvf folder_name –> for compressing and creating the package for particular folder tar -xzvf package_name –> for extracting the package
21 What are the diffrent commands avilable to check the disk usage df - This command is used to check the free disk space du - This command is used to check the directory wise disk space dfspace - This command is used to check the free disk space in term of MB
22 what are the diffrent communication commands available in the shell? mail - whcih will call the mailbinary to send and read mails news - which is used to read the system wide news to standard output wall(write to all) - It is used to send out shutdown messages to all users motd(message of the day) -
23 How to find out the totak disk space used by a specific user du -s/home/user_name
24 How to debug the problems encountered in shell script/program? –> By adding logs –> By set -x
25 what is the diffrence between = and == ? = –> used for assigning value to the variable == –> used for string comparison The = operator in test command or within [] will used for comparison
26 How to open a read only file in a shell vi -R file_name
27 How can the contents of a file inside the jar be read without extracting in a shell script? tar -tvf package_name.tar t –> table 0f contents v –> verbose f –> file
28 How can you pass parameters to the shell script ? ./script.sh param1 param2
29 How to find all the files modified in less than 3 days and print the record count odf each? find . -type f -mtime -3 -exec ls -l {} \; > last3days.txt -type f –> search only for files -mtime -3 –> for last three days
30 Throw a error message if 2 arguments are not passed if [ $# -ne 2] echo “Enter two parameters”
Here $# will get the no of parameters passed
31 Calculate a real number calculation directly from terminal and not any shell script echo 7.56 + 4.432 | bc
32 How can you get the value of pi till a 100 decimal places echo “scale=100; 4*a(1)” | bc -l
33 For debugging use set -x will print the actual script and also the errors in the script
Convert this format using shell script (YYYYMMDD -> 1st jan 2021)
date +'%d %b %Y'
12 Jan 2021