Blog - Midnightmonk.com

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For more recent and up-to-date news and technical articles, kindly visit my NEW blog at midnightmonk.com


At midnightmonk.com you will find my most recent and up-to-date articles and posts related to all technical and  social topics and events.


The blogs is mostly dedicated to :


Programming languages such as PHP, PERL, Ruby, Shell scripting, etc....,
Databases such as MySql, Postgresql, MSSQL, etc....
Programming code snippets, tips and tricks...
Application design concepts and techniques.
Database design concepts and techniques...


And lots lots more.... 


So please visit my blog and keep posting your comments, they are very  much appreciated..


Thanks,
Pa Arun Kumar.

BASH Shell change the color of shell prompt under Linux or UNIX

You can change the color of your shell prompt to impress your friend or to make your own life quite easy while working at command prompt.
In the Linux default shell is BASH.
Your current prompt setting is stored in PS1 shell variable. There are other variables too, like PS2, PS3 and PS4.
Bash displays the primary prompt PS1 when it is ready to read a command, and the secondary prompt PS2 when it needs more input to complete a command. Bash allows these prompt strings to be customized by inserting a number of backslash-escaped special characters.

Task: Display current BASH prompt (PS1)

Use echo command to display current BASH prompt:
$ echo $PS1


Output:

[\\u@\h \\W]\\$

By default the command prompt is set to: [\u@\h \W]\$. Backslash-escaped special characters are decoded as follows:

• \u: Display the current username
• \h: Display the hostname
• \W: Print the current working directory

Task: Modify current BASH prompt

Use export command to setup a new shell prompt:


$ export PS1="[\\u@\\H \\W \\@]\\$"


Where,

• \H: Display FQDN hostname
• \@: Display current time in 12-hour am/pm format

Task: Add colors to the prompt

To add colors to the shell prompt use the following export command syntax:
'\e[x;ym $PS1 \e[m'
Where,

• \e[ Start color scheme
• x;y Color pair to use (x;y)
• $PS1 is your shell prompt
• \e[m Stop color scheme

To set a red color prompt, type the command:

$ export PS1="\e[0;31m[\u@\h \W]\$ \e[m "

List of Color code

Color	Code
Black	0;30
Blue	0;34
Green	0;32
Cyan	0;36
Red	0;31
Purple	0;35
Brown	0;33
Blue	0;34
Green	0;32
Cyan	0;36
Red	0;31
Purple	0;35
Brown	0;33

Replace digit 0 with 1 to get light color version.

Task: How to make the prompt setting permanent

Your new shell prompt setting is temporary i.e. when you logout setting will be lost. To have it set everytime you login to your workstation add above export command to your .bash_profile file or .bashrc file.
$ cd
$ vi .bash_profile
OR
$ vi .bashrc
Append export line:
export PS1="\e[0;31m[\u@\h \W]\$ \e[m"
Save and close the file.

tput command

You can also use tput command. For example display RED prompt use tput as follows:
export PS1="\[$(tput setaf 1)\]\u@\h:\w $ \[$(tput sgr0)\]"

handy tput commands

• tput bold - Bold effect
• tput rev - Display inverse colors
• tput sgr0 - Reset everything
• tput setaf {CODE}- Set foreground color, see color {CODE} below
• tput setab {CODE}- Set background color, see color {CODE} below

Colors {code} code for tput command

Color {code}	Color
0	Black
1	Red
2	Green
3	Yellow
4	Blue
5	Magenta
6	Cyan
7	White

Read the man page of bash and tput command for more information.

Converting Unix to Windows and back

 In vim, use :set ff=unix to convert to Unix; use :set ff=dos to convert to Windows.

Remove ^M characters at end of lines in vi

:%s/{Ctrl+V}{Ctrl+M}//{Enter}

Recursively download entire websites

wget -r -p -U Mozilla http://www.mywebsite/thedownloadurl.html

The most important command line options are --limit-rate= and --wait=. You should add --wait=20 to pause 20 seconds between retrievals, this makes sure you are not manually added to a blacklist. --limit-rate defaults to bytes, add K to set KB/s. Example:

wget --wait=20 --limit-rate=20K -r -p -U Mozilla http://www.mywebsite/thedownloadurl.html

Use --no-parent

--no-parent is a very handy option that guarantees wget will not download anything from the folders beneath the folder you want to acquire. Use this to make sure wget does not fetch more than it needs to if just just want to download the files in a folder.

Find file in folders recursively

Case sensitive

find . -name "index.*" -type f -print

Case insensitive :

find . -iname "index.*" -type f -print

File write or append based on condition

use autodie;
use File::Copy 'copy';
my $append = ...;  # If true append, else overwrite.
open my $fh, $append ? ">>" : ">", LOG;
copy "tmp", $fh;

Or:

my $append = ...;  # If true append, else overwrite.
system "cat tmp " . ($append ? ">>" : ">") . " LOG" and die;

Search and Replacing digits/integers

Replacing with out length restriction :=> :%s/\(\d\+\)/VALUE(\1)/g


Replacing with length restriction :=> :%s/\(\d\{10}\)/VALUE(\1)/g

Replacing space with tab

:%s/\s\+$/\t/g

Trapping SIGNAL in Bash

#!/bin/bash
# bash trap command
trap bashtrap INT
# bash clear screen command
clear;
# bash trap function is executed when CTRL-C is pressed:
# bash prints message => Executing bash trap subrutine !
bashtrap()
{
echo "CTRL+C Detected !...executing bash trap !"
}
# for loop from 1/10 to 10/10
for a in `seq 1 10`; do
echo "$a/10 to Exit."
sleep 1;
done
echo "Exit Bash Trap Example!!!"