How to clean log file?

> logfile

or

cat /dev/null > logfile

Change The Color of My Shell Prompt Under Linux or UNIX Permanently

$ cd
$ vi .bash_profile

OR
$ vi $HOME/.bashrc
Append the following line:
export PS1="\e[0;31m[\u@\h \W]\$ \e[m"
Save and close the file.

To do this changing you must logout an login again.

A list of color codes

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

Note: You need to replace digit 0 with 1 to get light color version.

----------------------------- In Ubuntu 14.4 --------------------------

Run the following command in a terminal:

gedit ~/.bashrc

When .bashrc opens, locate and uncomment force_color_prompt=yes (that is, remove the hash, so it no longer looks like: #force_color_prompt=yes).

Save the file, and open a new terminal window, and you should already see a change (the prompt should be Light Green, which is defined by 1;32). You can then change any colour value you like; eg: 0;35 = Purple.

To edit the colour values, locate the following section, and change the default values with some of the examples listed further down:

if [ "$color_prompt" = yes ]; then
    PS1=’${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;31m\]\w\[\033[00m\]\$ ‘
else
    PS1=’${debian_chroot:+($debian_chroot)}\u@\h:\w\$ ‘
fi

You can check out this Bash colour chart for a full range of colour values, but here are a few basic ones you can play around with (note that “Light” isn’t what you might think – it actually means “bold”): Black 0;30 – Dark Gray 1;30 – Blue 0;34 – Light Blue 1;34 – Green 0;32 – Light Green 1;32 – Cyan 0;36 – Light Cyan 1;36 – Red 0;31 – Light Red 1;31 – Purple 0;35 – Light Purple 1;35 – Brown 0;33 – Yellow 1;33 – Light Gray 0;37 – White 1;37

For example, here is the line that I use it:

PS1='${debian_chroot:+($debian_chroot)}\[\033[01;35m\]\u@\h\[\033[00m\]:\[\033[01;34m\] \w\[\033[01;37m\] > '

How do I change the color of my shell prompt under Linux or Unix operating systems?

You can change the color of your shell prompt to impress your friend or to make your own life quite easy while working at the command prompt. BASH shell is the default under Linux and Apple OS X. Your current prompt setting is stored in a shell variable called PS1. There are other variables too, like PS2, PS3 and PS4.

Tutorial details

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)