show-ref --hash=len, --abbrev=len, and --abbrev

This teaches show-ref to abbreviate the object name.

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-show-ref.txt

@@ -9,7 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git-show-ref' [-q|--quiet] [--verify] [-h|--head] [-d|--dereference]
-	     [-s|--hash] [--tags] [--heads] [--] <pattern>...
+	     [-s|--hash] [--abbrev] [--tags] [--heads] [--] <pattern>...
 
 DESCRIPTION
 -----------
@@ -37,14 +37,13 @@ OPTIONS
 
 -d, --dereference::
 
-	Dereference tags into object IDs. They will be shown with "^{}"
+	Dereference tags into object IDs as well. They will be shown with "^{}"
 	appended.
 
 -s, --hash::
 
 	Only show the SHA1 hash, not the reference name. When also using
-	--dereference the dereferenced tag will still be shown after the SHA1,
-	this maybe a bug.
+	--dereference the dereferenced tag will still be shown after the SHA1.
 
 --verify::
 
@@ -52,6 +51,11 @@ OPTIONS
 	Aside from returning an error code of 1, it will also print an error
 	message if '--quiet' was not specified.
 
+--abbrev, --abbrev=len::
+
+	Abbreviate the object name.  When using `--hash`, you do
+	not have to say `--hash --abbrev`; `--hash=len` would do.
+
 -q, --quiet::
 
 	Do not print any results to stdout. When combined with '--verify' this

builtin-show-ref.c

@@ -6,12 +6,13 @@
 static const char show_ref_usage[] = "git show-ref [-q|--quiet] [--verify] [-h|--head] [-d|--dereference] [-s|--hash] [--tags] [--heads] [--] [pattern*]";
 
 static int deref_tags = 0, show_head = 0, tags_only = 0, heads_only = 0,
-	found_match = 0, verify = 0, quiet = 0, hash_only = 0;
+	found_match = 0, verify = 0, quiet = 0, hash_only = 0, abbrev = 0;
 static const char **pattern;
 
 static int show_ref(const char *refname, const unsigned char *sha1, int flag, void *cbdata)
 {
 	struct object *obj;
+	const char *hex;
 
 	if (tags_only || heads_only) {
 		int match;
@@ -51,13 +52,16 @@ match:
 	}
 	if (quiet)
 		return 0;
+
+	hex = find_unique_abbrev(sha1, abbrev);
 	if (hash_only)
-		printf("%s\n", sha1_to_hex(sha1));
+		printf("%s\n", hex);
 	else
-		printf("%s %s\n", sha1_to_hex(sha1), refname);
+		printf("%s %s\n", hex, refname);
 	if (deref_tags && obj->type == OBJ_TAG) {
 		obj = deref_tag(obj, refname, 0);
-		printf("%s %s^{}\n", sha1_to_hex(obj->sha1), refname);
+		hex = find_unique_abbrev(obj->sha1, abbrev);
+		printf("%s %s^{}\n", hex, refname);
 	}
 	return 0;
 }
@@ -94,6 +98,29 @@ int cmd_show_ref(int argc, const char **argv, const char *prefix)
 			hash_only = 1;
 			continue;
 		}
+		if (!strncmp(arg, "--hash=", 7) ||
+		    (!strncmp(arg, "--abbrev", 8) &&
+		     (arg[8] == '=' || arg[8] == '\0'))) {
+			if (arg[3] != 'h' && !arg[8])
+				/* --abbrev only */
+				abbrev = DEFAULT_ABBREV;
+			else {
+				/* --hash= or --abbrev= */
+				char *end;
+				if (arg[3] == 'h') {
+					hash_only = 1;
+					arg += 7;
+				}
+				else
+					arg += 9;
+				abbrev = strtoul(arg, &end, 10);
+				if (*end || abbrev > 40)
+					usage(show_ref_usage);
+				if (abbrev < MINIMUM_ABBREV)
+					abbrev = MINIMUM_ABBREV;
+			}
+			continue;
+		}
 		if (!strcmp(arg, "--verify")) {
 			verify = 1;
 			continue;