diff --git a/audio/metaflac-field2field.sh b/audio/metaflac-field2field.sh
index 4b3af05..53a4a63 100755
--- a/audio/metaflac-field2field.sh
+++ b/audio/metaflac-field2field.sh
@@ -18,41 +18,45 @@
 
 #set -x
 
-print_usage()
-{
-    echo "Usage:"
-    echo "  $0 <ACTION> <SRC_FIELD> <DST_FIELD> <FILE.flac> [ <FILE2.flac> [...] ]"
-    echo "<ACTION> : copy | move | rmcopy | mvcopy"
-    echo "  copy: each occurrence of SRC_FIELD is duplicated to create an occurrence of"
-    echo "        DST_FIELD; all the existing occurrences of SRC_FIELD and DST_FIELD are"
-    echo "        kept."
-    echo "  move: each occurrence of SRC_FIELD is renamed to create an occurrence of"
-    echo "        DST_FIELD; the existing occurrences of DST_FIELD are kept."
-    echo "  rmcopy: the existing occurrences of DST_FIELD are deleted, then each"
-    echo "          occurrence of SRC_FIELD is duplicated to create an occurrence"
-    echo "          of DST_FIELD; the occurrences of SRC_FIELD are kept."
-    echo "  rmmove: the existing occurrences of DST_FIELD are deleted, then each"
-    echo "          occurrence of SRC_FIELD is renamed to create an occurrence of"
-    echo "          DST_FIELD."
-    exit 1
-}
+USAGE=$(cat <<EOF
+Usage:
+  $0 <ACTION> <SRC_FIELD> <DST_FIELD> <FILE.flac> [ <FILE2.flac> [...] ]
+
+<ACTION> : copy | move | rmcopy | mvcopy
+  copy: each occurrence of SRC_FIELD is duplicated to create an occurrence of
+        DST_FIELD; all the existing occurrences of SRC_FIELD and DST_FIELD are
+        kept.
+  move: each occurrence of SRC_FIELD is renamed to create an occurrence of
+        DST_FIELD; the existing occurrences of DST_FIELD are kept.
+  rmcopy: the existing occurrences of DST_FIELD are deleted, then each
+          occurrence of SRC_FIELD is duplicated to create an occurrence
+          of DST_FIELD; the occurrences of SRC_FIELD are kept.
+  rmmove: the existing occurrences of DST_FIELD are deleted, then each
+          occurrence of SRC_FIELD is renamed to create an occurrence of
+          DST_FIELD.
+EOF
+)
 
 # Right number of arguments?
 if [ $# -lt 4 ] ; then
-    echo "Wrong number of arguments!"
+    echo "Wrong number of arguments!" >&2
     print_usage
 fi
 
-ACTION=$1
+ACTION="$1"
 shift
 
 # Known action type?
-case $ACTION in
+case "$ACTION" in
     copy) ;;
     move) ;;
     rmcopy) ;;
     rmmove) ;;
-    *) echo "Action unknown \"$ACTION\"!" ; print_usage ;;
+    *)
+        printf 'Action unknown "%s"!\n\n' "$ACTION" >&2
+        printf '%s\n' "$USAGE" >&2
+        exit 1
+        ;;
 esac
 
 SRC_FIELD=$1
@@ -60,28 +64,28 @@ shift
 DST_FIELD=$1
 shift
 
-echo "Source field: $SRC_FIELD"
-echo "Destination field: $DST_FIELD"
-echo "Action: $ACTION"
+printf 'Source field: %s\n' "$SRC_FIELD"
+printf 'Destination field: %s\n' "$DST_FIELD"
+printf 'Action: %s\n' "$ACTION"
 
 echo "Processing files..."
 
-if echo $ACTION | egrep '^rm' >/dev/null ; then
-    echo "Deleting field $DST_FIELD on each file..."
-    metaflac --remove-tag=$DST_FIELD "$@"
+if echo "$ACTION" | grep '^rm' >/dev/null ; then
+    printf 'Deleting field "%s" on each file...\n' "$DST_FIELD"
+    metaflac --remove-tag="$DST_FIELD" "$@"
 fi
 
 for file in "$@" ; do
-    echo "Setting field \"$DST_FIELD\" on file: $file"
-    metaflac --show-tag=$SRC_FIELD "$file" | sed 's/^[A-Z]\+=//' | while read c1 ; do
-    echo "Adding $DST_FIELD=$c1..."
-    metaflac --set-tag=$DST_FIELD="$c1" "$file"
+    printf 'Setting field "%s" on file: "%s"\n' "$DST_FIELD" "$file"
+    metaflac --show-tag="$SRC_FIELD" "$file" | sed 's/^[A-Z]\+=//' | while read -r c1 ; do
+    printf 'Adding "%s"...\n' "$DST_FIELD=$c1"
+    metaflac --set-tag="$DST_FIELD"="$c1" "$file"
 done
 done
 
-if echo $ACTION | egrep 'move$' >/dev/null ; then
-    echo "Deleting $SRC_FIELD on each file..."
-    metaflac --remove-tag=$SRC_FIELD "$@"
+if echo "$ACTION" | grep 'move$' >/dev/null ; then
+    printf 'Deleting "%s" on each file...\n' "$SRC_FIELD"
+    metaflac --remove-tag="$SRC_FIELD" "$@"
 fi
 
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