Follow The Path
For security reasons in Unix/Linux variant Operating Systems, the current directory is not included in the PATH.
Its a measure to plug possible security holes. You can't run commands in the current directory without specifically calling them.
To stop nasties writing a vicious shell script, placing the script in an innocent location such as /tmp and getting root to run the script. Would root run a nefarious script? If the script was named 'ls' and root did a listing, the script would automatically run.
To prevent such scenarious taking place, by default the current directory is excluded from the PATH.
That can be a pain if you want to run simple scripts yourself. The solution? Add your current directory to the PATH.
Add the following to .bash_profile or .profile start up files in your home dir:
Warning!!! Do not change root user's PATH.