Unfortunaly the command brew is not available : command not found
The homebrew (brew) package manager is installed into /usr/local/bin, which is among the standard paths configured by OS X, and is found, providing you have the PATH environment variable minimally exported in one of the following files as:
export PATH=$PATH
The default bash shell search order on Terminal launch:
~/.bash_profile
~/.bash_login
~/.profile
If you run another bash shell from the command line, it will then read the personal initialization file (~/.bashrc) from your login directory. Personally, I have all of my personal stuff including PATH export in this file, and reference it from the ~/.bash_profile file as:
[[ -s ~/.bashrc ]] && source ~/.bashrc
I have single file maintenance restricted to the ~/.bashrc file. This file is processed first, if you launch a second bash shell from the login bash shell.
Read the invocation section of the bash(1) man page for further information.
(whereis command is not giving me any path)
The whereis(1) command says it will search standard binary directories -- just not /usr/local/bin, despite this being one of the default OS X search paths. Try which(1).