find . -name "*.bb" -type f -exec grep -H "SRC_URI" {} \; | cut -d "=" -f2 | sed 's/^[ \t]*//;s/[ \t]*$//' >> git.txt

This command searches for all files with the .bb extension in the current directory and its subdirectories, and then searches for the string "SRC_URI" in each of these files. It then extracts the value of the "SRC_URI" key using the cut command and removes any leading or trailing whitespace using the sed command. Finally, it appends the extracted values to the file "git.txt".