select one of several checksum commands

contrib/hooks/post_encrypt

@@ -27,63 +27,73 @@ IFS=$'\n'
 YADM_ENCRYPT_INCLUDE_FILES=( $YADM_ENCRYPT_INCLUDE_FILES )
 IFS="$OLD_IFS"
 
-CHECKSUM_ALGORITHM="512"
-CHECKSUM_ALGORITHM_NAME="SHA-512"
-WARNING_MESSAGE="No checksums were created."
+WARNING_MESSAGE="No checksums were created"
 
 
-function print_warning_and_exit {
-    MESSAGE=$1
+function get_checksum_command {
+    # check if "shasum" exists and supports the algorithm (which is
+    # tested by sending an empty string to "shasum")
+    if command -v "shasum" > /dev/null && echo -n | shasum --algorithm "256" &> /dev/null; then
+        echo "shasum --algorithm 256"
+    # check if "sha256sum" exists
+    elif command -v "sha256sum" > /dev/null; then
+        echo "sha256sum"
+    # check if "gsha256sum" exists
+    elif command -v "gsha256sum" > /dev/null; then
+        echo "gsha256sum"
+    else
+        # display warning in bright yellow
+        echo -e "\033[1;33m" >&2
+        echo -n "WARNING: \"shasum\", \"sha256sum\" and \"gsha256sum\" not found.   $WARNING_MESSAGE." >&2
 
-    # set output color to yellow
-    echo -e "\033[1;33m"
-    echo "WARNING: $MESSAGE  $WARNING_MESSAGE"
+        # reset output color
+        echo -e "\033[0m" >&2
 
-    # reset output color
-    echo -e "\033[0m"
+        # signal error
+        return 1
+    fi
+}
 
+
+# get checksum command
+CHECKSUM_COMMAND=$(get_checksum_command)
+ERROR_CODE=$?
+
+# no command found
+if [ $ERROR_CODE -ne 0 ]; then
+    # return original exit status of yadm command
     exit "$YADM_HOOK_EXIT"
-}
+fi
 
-
-function ensure_command {
-    COMMAND_NAME=$1
-
-    # check if command exists
-    if ! command -v "$COMMAND_NAME" > /dev/null; then
-        print_warning_and_exit "command \"$COMMAND_NAME\" not found."
-    fi
-}
-
-
-function ensure_algorithm {
-    # check if "shasum" supports algorithm by hashing an empty string
-    echo -n | shasum --algorithm "$CHECKSUM_ALGORITHM" &> /dev/null
-
-    if [ $? -ne 0 ]; then
-        print_warning_and_exit "\"shasum\" does not support $CHECKSUM_ALGORITHM_NAME."
-    fi
-}
-
-
-# check if "shasum" exists and supports algorithm
-ensure_command shasum
-ensure_algorithm
-
-# empty checksum file
+# empty (or create) checksum file
 echo -n > "$YADM_CHECKSUMS"
 
 # calculate checksums for encrypted files
 for included in ${YADM_ENCRYPT_INCLUDE_FILES[*]}; do
-    shasum --algorithm $CHECKSUM_ALGORITHM "$included" >> "$YADM_CHECKSUMS"
+    # highlight any errors in red
+    echo -en "\033[0;31m"
 
-    # signal errors
-    if [ $? -ne 0 ]; then
-        exit $?
+    # calculate checksums
+    $CHECKSUM_COMMAND "$included" >> "$YADM_CHECKSUMS"
+    ERROR_CODE=$?
+
+    # reset output color
+    echo -ne "\033[0m"
+
+    # handle errors
+    if [ $ERROR_CODE -ne 0 ]; then
+        # display warning in bright yellow
+        echo -e "\033[1;33m" >&2
+        echo -n "WARNING: an error occurred.  Please inspect the checksum file." >&2
+
+        # reset output color
+        echo -e "\033[0m" >&2
+
+        # exit and signal error
+        exit $ERROR_CODE
     fi
 done
 
-echo "Wrote checksums: $YADM_CHECKSUMS ($CHECKSUM_ALGORITHM_NAME)"
-
-# return exit status of the yadm command
+# announce success and return original exit status of yadm command
+echo "Wrote SHA-256 checksums: $YADM_CHECKSUMS"
 exit "$YADM_HOOK_EXIT"