Script for automatically matching keyword in text content

Text Content automatically matches keyword scripts-general Linux technology-Linux technology and application information. For more information, see the following. Environment: A linux ftp server installed with pureftp creates a directory for each user and allocates a certain amount of space, normal users can copy some files to it and download them to other media for debugging;
Concept: aaa copies a file to its own ftp directory/ftp/aaa. It may be a text file or a folder containing multiple files, when the user aaa copies data to his own directory, a script is automatically triggered (this script defines some keywords in advance, such as if ), when this script detects that the written file or folder file contains the keyword if, it rejects writing to the/ftp/aaa directory;
Q: Is there a file content comparison function in linux?
I just learned about linux and started a short time ago. Could you please help me to see if this can be solved? If yes, can you give me a rough command for reference, or is it possible to solve this problem through other methods, in fact, the purpose is to add a verification measure when the user writes the ftp personal directory. This verification measure can automatically check whether the content of the written file matches the predefined conditions or keywords.
Please help me to see if I can solve the problem. If I do not understand it, I will clearly explain it in detail.