On a new install of Ubuntu installing Valet worked fine at the composer stage but when trying to run valet commands resulted in 'Valet: command not found" errors. The problem is composer has not been added to the $PATH I tried adding the composer path to .profile which I think was not been executed the way I thought. Instead, I updated the path inside .bash_profile:
~/.bash_profile
Then updated my path:
export PATH=~/.composer/vendor/bin:$PATH
To ensure it took effect I reloaded the profile by running the command:
source ~/.profile
After then I was able to run Valet commands.