So there are few places where terminal looks for commands. This places are stored in your $PATH variable. Think of it as a global variable where terminal iterates over to look up for any command. This are usually binaries look how /bin folder is usually referenced.
/bin folder has lots of executable files inside it. Turns out this are command. This different folder locations are stored inside one Global variable i.e. $PATH separated by :
Now usually programs upon installation takes care of updating PATH & telling your terminal that hey i can be all commands inside my bin folder.
Turns out MySql doesn't do it upon install so we manually have to do it.
We do it by following command,
export PATH=$PATH:/usr/local/mysql/bin
If you break it down, export is self explanatory. Think of it as an assignment. So export a variable PATH with value old $PATH concat with new bin i.e. /usr/local/mysql/bin
This way after executing it all the commands inside /usr/local/mysql/bin are available to us.
There is a small catch here. Think of one terminal window as one instance of program and maybe something like $PATH is class variable ( maybe ). Note this is pure assumption. So upon close we lose the new assignment. And if we reopen terminal we won't have access to our command again because last when we exported, it was stored in primary memory which is volatile.
Now we need to have our mysql binaries exported every-time we use terminal. So we have to persist concat in our path.
You might be aware that our terminal using something called dotfiles to load configuration on terminal initialisation. I like to think of it's as sets of thing passed to constructer every-time a new instance of terminal is created ( Again an assumption but close to what it might be doing ). So yes by now you get the point what we are going todo.
.bash_profile is one of the primary known dotfile.
So in following command,
echo 'export PATH=$PATH:/usr/local/mysql/bin' >> ~/.bash_profile
What we are doing is saving result of echo i.e. output string to ~/.bash_profile
So now as we noted above every-time we open terminal or instance of terminal our dotfiles are loaded. So .bash_profile is loaded respectively and export that we appended above is run & thus a our global $PATH gets updated and we get all the commands inside /usr/local/mysql/bin.
P.s.
if you are not running first command export directly but just running second in order to persist it? Than for current running instance of terminal you have to,
source ~/.bash_profile
This tells our terminal to reload that particular file.
