Customizing your log in shell

Shell resource files:
Every time you log in, the UNIX shell searches your home directory for shell resource files to execute. These files, prefixed with a period, customize the UNIX session. Each shell has its own unique set of resource files. We'll discuss those for C-shell, the Korn shell, and the bash shell.

For the csh/tcsh shell, the two initialization files are the the the .cshrc (pronounced `dot-see-shirk') file, (alternatively tcsh accepts the either a .cshrc or .tcshrc file), and the (pronounced `dot-login') file. The .cshrc file is executed every time a new C shell is started. The .login is executed after the .cshrc file only when you initially log in. Generally, so that every new copy of the C shell will be able to use them, any alias and set commands should be placed in the file. Although it is also permissible to create a separate third file for aliases called .aliases. the .aliases file must be defined and executed as part of the .cshrc/.tcshrc file, just like the .env file on the Korn shell. In this case it is necessary to Environment variables are typically set in the .login file, as well as library and manual paths, and terminal settings. In many cases, this division isn't clear cut.

On login the ksh shell executes a profile file called .profile. The .profile is used to set environment variables and shell options. Aliases can also be put in the Profile file, but it's considered good practice to put them in a separate environment file called .env. The environment file is defined and executed as part of the .profile. This is different from how the C-shell resource files are handled. An example of a korn shell shows that its syntax is based on that of the Bourne shell.

On login the bash shell executes a resource file called .bashrc that is responsible for all the shell customization. An example of a bash shell shows that its syntax is similar to the Bourne and Korn shells.

Critical Aliases:
In my mind, the three most important aliases are for the mv, cp, and rm commands. The default behavior of the mv and cp commands over writes any existing file without warning. The default behavior of the rm command removes a file without warning. In UNIX once a file is removed, there is no easy or gauranteed way to get it back. The flag -i forces the mv, cp, and rm commands to ask for comformation before completing. I always add these aliases to any new account, because it can save you from making a careless mistake that wipes out important work.

In csh/tcsh shells, the syntax is:

alias mv '/usr/bin/mv -i '
alias cp '/usr/bin/cp -i '
alias rm '/usr/bin/rm -i '

Otherwise the syntax is:

alias mv='/usr/bin/mv -i '
alias cp='/usr/bin/cp -i '
alias rm='/usr/bin/rm -i '

Useful Aliases:
Some other useful aliases are:

alias c 'clear'
shorthand a command.
alias h 'history
alias ls 'ls -F' change the default behavior of a command.
alias cd 'cd \!*; ls' show the contents of a directory when you go to it.
alias exit 'logout' add new names to existing commands
alias print 'enscript -G2rc -dprintername' this one prints a text file as 2 columns.

In addition with the Bash useful functions came be defined, such as this one which automatically picks the correct way to extract an archive.

function extract()      # Handy Extract Program.
if [ -f $1 ] ; then
case $1 in
*.tar.bz2) tar xvjf $1 ;;
*.tar.gz) tar xvzf $1 ;;
*.bz2) bunzip2 $1 ;;
*.rar) unrar x $1 ;;
*.gz) gunzip $1 ;;
*.tar) tar xvf $1 ;;
*.tbz2) tar xvjf $1 ;;
*.tgz) tar xvzf $1 ;;
*.zip) unzip $1 ;;
*.Z) uncompress $1 ;;
*.7z) 7z x $1 ;;
*) echo "'$1' cannot be extracted" ;;
esac else echo "'$1' is not a valid file" fi }

If you know of any others, send them to me and I'll add them to the list.

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