Linux Basics – Hands-On Guide

Linux is an operating system based on UNIX OS, having high security. 
For those of you who are beginner in Linux, please follow along:

Here are some basic and important commands to run on Linux terminal:

1. To list the content of a directory
   • ls
   • ls -all
   • ll    i.e. long listing
2. To view system date, time and timezone
   • date
3. To see all Processes running on your Linux machine
   • ps
   • ps -ef
4. to create new directory i.e. hadoop
   • mkdir hadoop
5. to change/switch to new directory i.e. hadoop
   • cd hadoop
6. to create new file i.e. mapreduce.txt inside a directory
   • touch mapreduce.txt
   • nano mapreduce.txt
   • vi mapreduce.txt
7. to view content of a file
   • cat mapreduce.txt
   • more mapreduce.txt
   • head mapreduce.txt
     • this will show top 10 records of the file
   • tail mapreduce.txt
     • this will show the last 10 records of the file
8. lets put some content in this file
   • nano mapreduce.txt
   • then copy paste below content [6 lines] and save the file

101,java
201,scala
301,python
401,R
501,SAS
601,sas

1. Search specific word/content in a file ***very important
   • grep “word-to-search” filename
   • examples
     • grep “SAS” mapreduce.txt
     • grep -i “SAS” mapreduce.txt
       • -i is a flag that makes command case-insensitive i.e. Ignore Case
     • grep -n “SAS” mapreduce.txt
       • -n flag will print the line number of the file containing the match word
2. Redirection Operator: > and >>
   • this command will copy and over-write content of one file to another
     • cat mapreduce.txt > spark.txt
   • this command will copy but won’t over-write content of one file to another , i.e. it will append content to end of existing content inside the file
     • cat mapreduce.txt >> spark.txt
3. Pipeline Operator: |
   • this operator will pass the output of a command [on left hand side] as input to another command [on right hand side]

   ps -ef | grep -i "sh"
   ls -all | grep -i "hadoop"  

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For some programming experience, one can also try for loops and conditional statements [if then else] in Linux.

for i in {1..10}

do

echo $i

done

Also having sound understanding of sed and awk/gawk commands will help you clear most of the Linux and Shell Programming interviews.

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