Here is a good resource for popular Linux SSH Commands:

sudo

Prefix any Linux SSH command with "sudo" to run that command as an administrator at the root (most powerful) level of the system. Sudo also logs all commands and arguments.
STRUCTURE:  sudo [command]
[command] - the Linux SSH command your want to run as an administrator
COMMON OPTIONS: None
EXAMPLES:
sudo chmod 755 index.html
Runs the "chmod 755 index.html" command (which changes the permissions of index.html to 755) as an administrator. It is important to use "sudo" with this particular command because if you don't have permissions to update this file, it won't let you update it. Using "sudo" will let you update the permissions of the file no matter what, however, because the system will look at you like you are the admin (root) user.

grep

Searches within the body content of files for the input search parameter regular expression or word.
STRUCTURE:  grep [options] [search_pattern] [file_name]
[options] - the flags you want to set (see "common options" section)
[search_pattern] - the word or regular expression you are searching for
[file_name] - The path of the file you want to search. Use "*" to search all files in current directory
COMMON OPTIONS:
-i
Make search case-insensitive
-r
Recursive search (in addition to the current directory, search in all sub-directories too)
-w
Match the whole word instead of a substring of the word (Example: searching "Mark" will return "Marker", "Market", "Marked", etc in you results. If this flag is set, only files containing the word "Mark" will be returned. "Marker", "Market", "Marked", etc. will be skipped).
EXAMPLES:
grep -iwr "Goodbye" *
Searches all files within current directory and all sub-directories for the word "Goodbye". It must find the whole word "Goodbye" (-w), the search is case-insensitive (-i), and all subdirectories wil be searched as well (-r). The "*" is wild card in place of the file name, meaning all files will be searched.

grep -i "good" index.html
Searches the file in the current directory called "index.html" for the word "good". It is allowed to find the word "good" inside of another string because "-w" is not set (Goodbye will come back as found), the search is case-insensitive (-i), and it is only searching the file in the current directory called "index.html".