patch_strings_in_file

#!/usr/bin/env bash

# Function to replace content in a binary file
# see https://everydaywithlinux.blogspot.com/2012/11/patch-strings-in-binary-files-with-sed.html
function patch_strings_in_file() {
        local FILE="$1"
        local PATTERN="$2"
        local REPLACEMENT="$3"

        # Find all unique strings in FILE that contain the pattern 
        STRINGS=$(strings ${FILE} | grep ${PATTERN} | sort -u -r)

        if [ "${STRINGS}" != "" ]; then
                echo "File '${FILE}' contain strings with '${PATTERN}' in them:"

                for OLD_STRING in ${STRINGS}; do
                        # Create the new string with a simple bash-replacement
                        NEW_STRING=${OLD_STRING//${PATTERN}/${REPLACEMENT}}

                        # Create null terminated ASCII HEX representations of the strings
                        OLD_STRING_HEX="$(echo -n ${OLD_STRING} | xxd -g 0 -u -ps -c 256)00"
                        NEW_STRING_HEX="$(echo -n ${NEW_STRING} | xxd -g 0 -u -ps -c 256)00"

                        if [ ${#NEW_STRING_HEX} -le ${#OLD_STRING_HEX} ]; then
                                # Pad the replacement string with null terminations so the
                                # length matches the original string
                                while [ ${#NEW_STRING_HEX} -lt ${#OLD_STRING_HEX} ]; do
                                        NEW_STRING_HEX="${NEW_STRING_HEX}00"
                                done

                                # Now, replace every occurrence of OLD_STRING with NEW_STRING 
                                echo -n "Replacing ${OLD_STRING} with ${NEW_STRING}... "
                                hexdump -ve '1/1 "%.2X"' ${FILE} \
                                        | sed "s/${OLD_STRING_HEX}/${NEW_STRING_HEX}/g" \
                                        | xxd -r -p >${FILE}.tmp
                                chmod --reference ${FILE} ${FILE}.tmp
                                mv ${FILE}.tmp ${FILE}
                                echo "Done!"
                        else
                                echo "New string '${NEW_STRING}' is longer than old" \
                                        "string '${OLD_STRING}'. Skipping."
                        fi
                done
        fi
}

patch_strings_in_file "$1" "$2" "$3"