Path

A path is a special variable used to find the executable of a program. The shell searches $PATH when you enter a command.

which ls
/usr/bin/ls
echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/bin:/opt/cuda-10.1/bin:/usr/lib/jvm/default/bin ...
echo $PATH | sed 's/:/\n/g'
/usr/local/sbin
/usr/local/bin
/usr/bin
/opt/cuda-10.1/bin
/usr/lib/jvm/default/bin

- You can run a program without searching for its path

./hello
Hello World!

hello
bash: hello: command not found
sudo mv hello/usr/local/bin
hello
Hello World!