Find
Find is used to search the directory system for files.
find location options search pattern
find /home myfile.txt This will look in the /home folder for myfile.txt (if you leave out the location, find will look in the directory you are currently in.)
By default, find is case-sensitive. The above example will not find MYFILE.TXT. If you want the search to be case insensitive:
find -iname myfile.txt
The above will find all of the following: myfile.txt MYFILE.TXT MyFile.txt (etc...)