How to remove duplicate records from a file in Linux?

How to remove / delete duplicate records / lines from a file?

  Let us consider a file with the following content. The duplicate record is 'Linux' with 2 entries :

$ cat file
Unix
Linux
Solaris
AIX
Linux

grep vs awk : 10 examples of pattern search

"grep vs awk" does not mean comparison between awk and grep because there is no comparison to awk whatsoever from grep.  awk is a highly powerful programming language whereas grep is just a filtration tool. However, many of the things which is done using grep and few more commands can be done using a simple awk command. In this article, we will see the awk altenative for the frequently used grep commands.

Let us consisder a file with the following contents:

$ cat file
Unix
Linux
Solaris
AIX
Ubuntu
Unix

$IGNOREEOF vs ignoreeof

How to prevent your terminal from getting closed OR prevent from getting the user logged out on pressing Control-D?
  The answer to this is IGNOREEOF / ignoreeof. Let us see what is this IGNOREEOF and the difference between IGNOREEOF and ignoreeof.

Control-D:
   Many of the times we might have pressed some key only to realize that the terminal got closed or he got logged out from his account. The user gets logged out whenever an EOF character is pressed which is Control-D.  So, if the user happens to be in his login shell, then logically the Ctrl-D ends up in getting the user's terminal closed as well.

Bash/Bourne shell:
    In Bash/Bourne shell, the log-out from the user account can be prevented by using the environment variable IGNOREEOF.

8 examples to find sum of all columns / numbers in a line

How to find the sum of all numbers or columns in a line of a text / CSV file?
    In an earlier article, we discussed about different ways of how to sum all the numbers in a file. In this, we will see how to find the sum of all the numbers in a line, or in other words, sum of all the columns in a line.

Let us consider a file with the following contents:

$ cat file
20 30 21
33 33 32
12 21 12

perl - 15 examples of substr command

substr is a perl function to extract substring from a string. substring in Perl is little special compared to other languages due to some additional functionalities. Let us discuss the substr function with examples.

Syntax:

 substr(STRING, OFFSET,  LENGTH, REPLACEMENT)

where STRING - the actual string from which the substring is to be extracted
          OFFSET - the starting position from where to extract
          LENGTH - the number of characters to be extracted from OFFSET (Optional)
          REPLACEMENT - the string to be replaced (Optional)