Refactor 2ff(1)

The Unix philosophy teaches us that tools should strive to output only
necessary diagnostic information and also reflect errors properly with
the return value.
There were three subtle problems with 2ff:

   1) If the farbfeld-passthrough failed, it would return 1 instead
      of 1.
   2) If the first 8 bytes contained a NUL byte, bash would print
      an ugly warning message. Passing it through tr -d '\0' fixes
      that.
   3) Lack of comments. I added some to make the structure even
      clearer, also including using an if-else-structure.

I removed the 2ff error message; the tools themselves print proper
messages already.

1 files changed, 22 insertions, 20 deletions

diff --git a/2ff b/2ff
index bf58e5b..ef6f02d 100755
--- a/2ff
+++ b/2ff
@@ -1,36 +1,38 @@
 #!/bin/sh
+
+# arguments
 if [ "$#" -ne 0 ]; then
 	echo "usage: $0" >&2
 	exit 1
 fi
 
+# write input into temporary file
 TMP=$(mktemp)
 trap 'rm "$TMP"' EXIT
-
 cat > "$TMP"
 
-if [ "$(dd if="$TMP" bs=1 count=8 2>/dev/null)" = "farbfeld" ]; then
+# determine the mime-type
+if [ "$(dd if="$TMP" bs=1 count=8 2>/dev/null | tr -d '\0')" = "farbfeld" ]; then
 	cat "$TMP"
-	exit 0
-fi
+else
+	MIME=$(file -ib "$TMP" | cut -d ";" -f 1)
 
-FORMAT=$(file -ib "$TMP" | cut -d ";" -f 1)
-
-case "$FORMAT" in
-image/png)
-	png2ff < "$TMP"
-	;;
-image/jpeg)
-	jpg2ff < "$TMP"
-	;;
-*)
-	convert "$TMP" png:- 2>/dev/null | png2ff 2>/dev/null
-	;;
-esac
+	case "$MIME" in
+	image/png)
+		png2ff < "$TMP"
+		;;
+	image/jpeg)
+		jpg2ff < "$TMP"
+		;;
+	*)
+		convert "$TMP" png:- 2>/dev/null | png2ff 2>/dev/null
+		;;
+	esac
+fi
 
+# errors
 if [ $? -ne 0 ]; then
-	printf "%s: failed to convert from %s\n" "$0" "$FORMAT" >&2
 	exit 1
+else
+	exit 0
 fi
-
-exit 0