Allow 'contains' builtin to return index

Add an option -i/--index to the contains builtin to print the index
of first coincidence.

builtin.cpp

@@ -2717,6 +2717,7 @@ static int builtin_contains( parser_t &parser, wchar_t ** argv )
 	argc = builtin_count_args( argv );
 	int i;
 	wchar_t *needle;
+	int index=0;
 	
 	woptind=0;
 
@@ -2727,6 +2728,10 @@ static int builtin_contains( parser_t &parser, wchar_t ** argv )
 				L"help", no_argument, 0, 'h'
 			}
 			,
+			{
+				L"index", no_argument, 0, 'i'
+			}
+			,
 			{
 				0, 0, 0, 0
 			}
@@ -2739,7 +2744,7 @@ static int builtin_contains( parser_t &parser, wchar_t ** argv )
 
 		int opt = wgetopt_long( argc,
 					argv,
-					L"+h",
+					L"+hi",
 					long_options,
 					&opt_index );
 		if( opt == -1 )
@@ -2772,6 +2777,9 @@ static int builtin_contains( parser_t &parser, wchar_t ** argv )
 				builtin_unknown_option( parser, argv[0], argv[woptind-1] );
 				return STATUS_BUILTIN_ERROR;
 
+			case 'i':
+				index=1;
+				break;
 		}
 		
 	}
@@ -2790,6 +2798,7 @@ static int builtin_contains( parser_t &parser, wchar_t ** argv )
 		
 		if( !wcscmp( needle, argv[i]) )
 		{
+			if ( index ) append_format(stdout_buffer, L"%d\n", i-woptind );
 			return 0;
 		}
 	}

doc_src/contains.txt

@@ -5,6 +5,7 @@
 
 \subsection contains-description Description
 
+- \c -i or \c --index print the the word index
 - \c -h or \c --help display this message
 
 Test if the set VALUES contains the string KEY. Return status is 0 if