To use the grep command to search for a pattern in only .txt files when running in recursive mode, you can use the -r option to search recursively, and the --include option to specify the *.txt file pattern.
Here is the basic syntax for using the grep command to search for a pattern in only .txt files when running in recursive mode:
grep -r --include='*.txt' pattern directory
The pattern argument is a regular expression that specifies the text to search for. The directory argument is the directory to search recursively. The --include='*.txt' option tells grep to include only .txt files in the search.
For example, to search for the string "hello" in all .txt files in the /var/log directory and its subdirectories, you can use the following command:
grep -r --include='*.txt' hello /var/log
This will search for the string "hello" in all .txt files in the /var/log directory and its subdirectories, and display the lines that contain the string.
You can use other options and arguments to customize the search, such as the -i option to ignore case, or the -n option to display the line numbers of the matching lines.