The $usearch environment variable
Scripts in the UPARSE tutorials require an environment variable called $usearch. The value of the variable should be whatever you would type at the beginning of a usearch command line. This depends on the usearch version you have, the name of the usearch binary file and whether or not the directory with the usearch binary file is in your shell PATH.
Use the Bash export command to set the variable. For convenience, you can put the command in your .bash_profile or .bashrc file so that it is set every time you start a shell.
Example
export usearch=/usr/bin/usearch8.1.1803_i86linux32