I got the solution.thanks to thinkdigit forums.posting here hoping it helpes someone:
"deepclutch, these _alias and things are shell functions which are activated if you are using Bash Autocompletion features, normally by uncommenting its entry in $HOME/.bashrc
Open your /etc/bash_completion file and you will find all the function's bodies defined there."
Thanks rag.i already enabled bash autocompletion in debian and ubuntu
# enable programmable completion features (you don't need to enable
# this, if it's already enabled in /etc/bash.bashrc and /etc/profile
# sources /etc/bash.bashrc).
if [ -f /etc/bash_completion ]; then
for fedora/RH you need to get bashcompletion rpm installed for full programmable completion bash.here is one link for your distro:
check atrmps.net,dries,livna,dag's,rpmfind,rpmforge repos for more updated rpms.