Linux & Unix

Linux-commands: ssh tunneling remote server to localhost

To start a ssh tunnel from some machine ports 80 to your localhost port 2001 use the following syntax:

ssh -N -L 2001:localhost:80  somemachine

Enjoy !

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Linux-Commands: Rapidly invoke editor to type long and complex command

To type a long and complex command from linux command line can be painful.  Helpful might be to invoke an editor for writing the details.  You can easily invoke an editor by using the following command:

ctrl-x e

Enjoy !

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Linux Command: Run the last command as root

To run the last command as root you simply can use this command:

sudo !!

Enjoy !

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AWK in Linux

awk Linux Commands

What is Linux awk Command?

Explanation

awk COMMAND:
awk command is used to manipulate the text.This command checks each line of a file, looking for patterns that match those given on the command line.

SYNTAX:
The Syntax is
awk '{pattern + action}' {filenames}

OPTIONS:

-W version Display version information and exit.

-F Print help message and exit.

EXAMPLE:
Lets create a file file1.txt and let it have the following data:

Data in file1.txt
141516
151511
5566
5251

To print the second column data in file1.txt

awk '{print $2}' file1.txt

This command will manipulate and print second column of text file (file1.txt). The output will look like

15155625
To multiply the column-1 and column-2 and redirect the output to file2.txt:

awk '{print $1,$2,$1*$2}' file1.txt > file2.txt

Command Explanation:
$1: Prints 1st column
$2: Prints 2ndcolumn
$1*$2: Prints Result of $1 x $2
file1.txt: input file
symbolfile2.txt: output file

The above command will redirect the output to file2.txt and it will look like,
14 15 21015 15 2255 56 2805 25 125

Enjoy !

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Alias-Command in Linux

alias COMMAND:alias command allows you to create a shortcut to a command. As the name indicates, you can set alias/shortcut name for the commands/paths which is too longer to remember.

SYNTAX:The Syntax is 
alias [options] [ AliasName [ =String ] ]

OPTIONS:

-a Removes all alias definitions from the current shell execution environment.
-p Prints the list of aliases in the form alias name=value on standard output.

EXAMPLE:To create a shortcut temporarily:

alias lhost='cd /var/www/html'

This command will set lhost to cd /var/www/html/.

Now if you type lhost it will take you to the specified folder/directory.

To create a shortcut Permanently:
You can put your aliases into the /home/user/.bashrc file. It is good to add them at the end of the file.

alias home='cd /var/www/html/hscripts/linux-commands'

Now if you type home it will take you to the specified folder/directory.

To create a shortcut for a command:

alias c='clear'

This command will set c to clear.
Now if you type c it will clear the screen.

Enjoy !

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