Better Console Calculator Using bc

If we use expr for mathematical calculations on console (terminal), it is frustrating, and hard to remember syntax and escape sequences used in expr. :( This small tip will help us.

Just add following line in your .bashrc file (~/.bashrc).

function calc
{
echo "${1}" | bc -l;
}

Then update the shell environment by:

$ source ~/.bashrc

"calc" from the shell will work as follows:

$ calc 2+3
5
$ calc 1+2*3
7
$ calc 1.1*2
2.2
$ calc "(1+2)*3"
9
$ calc "(1+2)^3"
27
$ calc "s(.5)"
.47942553860420300027

Web Access through Proxy Server by Terminal Applications

In many companies/Universities, the web access is granted through Proxy Server (Usually SQUID; hence port 3128).
There are many terminal applications (run on command line interface), which access Internet/Web. For example:
wget (to download file), ftp, lynx/links (to access website), apt/yum (to download and install package). If we are behind
proxy, these applications do not work. The easy solution is to set some shell environment variables, explained below:

For accessing web(lynx/links) using a non-authenticated proxy:
$ export http_proxy="http://proxy.yourcompany.com:3128"

Verify that the setting took place
$ echo $http_proxy
http://proxy.yourcompany.com:3128

For accessing web(lynx/links) using a authenticated proxy:
$ export http_proxy="http://username:password@proxy.yourcompany.com:3128"

If you want the change to be permanent (there each time you open a terminal),
add the export line to .bashrc in your 'home' directory.
$ echo 'export http_proxy="http://proxy.yourcompany.com:3128"'″ >> ~/.bashrc

Secure HTTP (over SSL) access
$ export https_proxy="https://proxy.yourcompany.com:3128"

FTP access
$ export ftp_proxy="ftp://proxy.yourcompany.com:3128"

Shortcuts for Working in BASH (Bourne Again SHell)

Navigation
Left/right cursor key --- Move left/right in text
Ctrl+A --- Move to beginning of lIne
Ctrl+E --- Move to end of line
Ctrl+right arrow --- Move forward one word
Ctrl+left arrow --- Move left one word

Editing
Ctrl+U --- Delete everything behind cursor to start of line
Ctrl+K --- Delete from cursor to end of line
Ctrl+W --- Delete from cursor to beginning of word
Alt+D --- Delete from cursor to end of word
Ctrl+T --- Transpose characters on left and right of cursor
Alt+T --- Transpose words on left and right of cursor

Miscellaneous
Ctrl+L --- Clear screen (everything above current line)
Ctrl+U --- Undo everything since last command
Alt+R --- Undo changes made to the line
Ctrl+Y --- Undo deletion of word or line caused by using Ctrl+K, Ctrl+W, and so on
Alt+L --- Lowercase current word (from the cursor to end of word)


Note: If you find these shortcuts hard to remember and you know vi(m),
you can enable vi mode for editing command line using following command:

$ set -o vi

To enable vi mode from start of Bash, add following lines to your ~/.bashrc
# Start vi Mode for command line editing
set -o vi

Typing Error Correction at Command Line

Open your Bash Resource Config file

$ vim ~/.bashrc
...
alias vmi='vim'
alias mvi='vim'
...
$ mvi ~/.bashrc
will open .bashrc

Prevent Yourself from Disaster

Edit your .bashrc file
$ vi ~/.bashrc

# prevent overwriting to existing file, while using redirection
set -o noclobber

# useful aliases
alias mv='mv -i'
alias cp='cp -i'
alias rm='rm -i'