To find files by content on a Unix or Linux system, you can use the grep command.
Here is the basic syntax for using the grep command to find files by content:
grep [options] pattern [files]
The pattern argument is a regular expression that specifies the text to search for. The files argument is a list of files to search, or a directory to search recursively. If you do not specify any files, grep will search for the pattern in the standard input.
For example, to search for the string "hello" in all files in the current directory, you can use the following command:
grep hello *
This will search for the string "hello" in all files in the current directory, and display the lines that contain the string.
You can use the -r option to search recursively in a directory and its subdirectories.
For example, to search for the string "hello" in all files in the /var/log directory and its subdirectories, you can use the following command:
grep -r hello /var/log
This will search for the string "hello" in all files in the /var/log directory and its subdirectories, and display the lines that contain the string.
You can use the -l option to display the names of the files that contain the pattern, instead of the lines that contain the pattern.
For example:
grep -rl hello /var/log
This will search for the string "hello" in all files in the /var/log directory and its subdirectories, and display the names of the files that contain the string.
You can use other options and arguments to customize the search, such as the -i option to ignore case.