Is it possible to define a command in bash?

Alternative to aliasing

gb() { cd /media/Dan/evolution; }

This defines shell function gb, which takes no arguments, and performs cd /media/Dan/evolution. As with other suggeststions, this can be added to ~/.bashrc

It is possible, and alias is the command you're looking for. For example alias ll="ls -l" in bash will let you type ll instead of ls -l. Please note there are no spaces used when setting an alias. man alias can be useful as well.

Alternatively, it is possible to write a C program that calls the desired command and save it to /usr/bin.

#include <stdio.h>
#include <string.h>

int main () {
    char command[50]; //notice you can change this to fit your needs
    int return_val;

    strcpy( command, "echo \"cd /media/Dan/evolution\" | bash -i" );
    return_val = system(command); 

   //this is equivalent to entering the command in a new bash, 
   //which will return and exit

    return return_val;
}

To compile it, go to the directory where the source was saved (in bash) and execute (you may need sudo):

 gcc ./gb.c -o /usr/bin/gb

After further research here, I realized simply throwing your command in system() won't work for bash built in commands. That's why you need to create an instance of an interactive bash and echo your commands to it. It's just overly complicated and probably useless, unless you want to, let's say, shorten a call to a shell script (some_script instead of sh ~/radgeRayden/Scripts/some_script).

Reference for the system() function