Tip: Remove Duplicate Lines in File Using Perl

Rai    Linux     code, duplicate, file, i/o, Linux, perl, process, syntax, tip

Here is little nifty code I found to snip or remove duplicate lines in a file using Perl. An example of a file that has duplicate lines looks like this:

/home/index.php
/home/links.php
/home/index.php

The result we want to achieve is this:

/home/index.php
/home/links.php

And here goes the code:

$ftmp = 'file.txt';
my %match = ();
{
local @ARGV = ($ftmp);
local $^I = '.tmp';
while(<>){
$match{$_}++;
next if $match{$_} > 1;
print;
}
}

The original file, file.txt, has its duplicate lines removed.

Tip: How to Use watch Command

Rai    Linux     command, free, Linux, ls, syntax, tip, watch

I have never known that there is a command in Linux called watch. Basically, watch runs a program in a period of time, and displaying the output in real time.

watch command syntax is very simple. One typical use of the command watch is running it with traceroute. This is one example:

watch 'traceroute google.com'

This will run the traceroute command, display the output and when it is done, it repeats the process again.

Here a couple more examples of the watch command:

watch -n 10 free -m

This command will run the command free in ten-second intervals, and display the output.

watch -n 3 'cat /proc/interrupts'

This command will display the interrupts in 3-second intervals.