The commands you posted do nothing useful — they run
grep on files whose name ends with
2, and recursively in directories whose name ends with
2. There's a missing space after
* (the space after
> is permitted but not useful and more confusing than anything):
grep -iHlnr 'filesman' * 2>/dev/null
grep -iHlnr 'eval.*base64_decode' * 2>/dev/null
This searches for files containing
filesman, or containing
eval followed by
base64_decode on the same line, in the current directory and its subdirectories recursively. The search is case-insensitive. Look at the manual of grep for the exact meaning of each option.
Calling that “malware finding” is a gross exaggeration. It's probably looking for PHP malware, but it might return some legitimate files as well and it only finds a few specific malwares.