libexec/bats: Consolidate, update usage

Per @sublimino's suggestion in sstephenson#126, `usage()` and `help()` have been
combined into `usage()`. Also updates the format of the `Usage:` stanza
to make it more readable.

Also adds the `BATS_VERSION` environment variable, which seems like a
reasonable item to export. This implementation is in conflict with
the change @jasonkarns made in sstephenson#124, though as small change to that
PR should bring it in line.

libexec/bats-core/bats

@@ -1,14 +1,10 @@
 #!/usr/bin/env bash
 set -e
 
-version() {
-  printf 'Bats 1.1.0\n'
-}
+export BATS_VERSION='1.1.0'
 
-usage() {
-  version
-  printf '%s\n' \
-    'Usage: bats [-h] [-c] [-f <regex>] [-r] [-p | -t] <test> [<test> ...]'
+version() {
+  printf 'Bats %s\n' "$BATS_VERSION"
 }
 
 abort() {
@@ -17,15 +13,18 @@ abort() {
   exit 1
 }
 
-help() {
+usage() {
+  local cmd="${0##*/}"
   local line
-  usage
+
   while IFS= read -r line; do
     printf '%s\n' "$line"
   done <<END_OF_HELP_TEXT
+Usage: $cmd [-cr] [-f <regex>] [-p | -t] <test>...
+       $cmd [-h | -v]
 
   <test> is the path to a Bats test file, or the path to a directory
-  containing Bats test files.
+  containing Bats test files (ending with ".bats").
 
   -c, --count      Count the number of test cases without running any tests
   -f, --filter     Filter test cases by names matching the regular expression
@@ -92,7 +91,8 @@ fi
 while [[ "$#" -ne 0 ]]; do
   case "$1" in
   -h|--help)
-    help
+    version
+    usage
     exit 0
     ;;
   -v|--version)

test/bats.bats

@@ -7,15 +7,15 @@ fixtures bats
   run bats
   [ $status -eq 1 ]
   [ "${lines[0]}" == 'Error: Must specify at least one <test>' ]
-  [ "${lines[2]%% *}" == 'Usage:' ]
+  [ "${lines[1]%% *}" == 'Usage:' ]
 }
 
 @test "invalid option prints message and usage instructions" {
   run bats --invalid-option
   [ $status -eq 1 ]
   emit_debug_output
   [ "${lines[0]}" == "Error: Bad command line option '--invalid-option'" ]
-  [ "${lines[2]%% *}" == 'Usage:' ]
+  [ "${lines[1]%% *}" == 'Usage:' ]
 }
 
 @test "-v and --version print version number" {