Added expression argument to forcibly set expression if required

acceptance_tests/basic.sh

@@ -2,6 +2,7 @@
 
 setUp() {
   rm test*.yml || true
+  rm .xyz -f
 }
 
 testBasicEvalRoundTrip() {
@@ -16,6 +17,18 @@ testBasicPipeWithDot() {
   assertEquals "a: 123" "$X"
 }
 
+testBasicExpressionMatchesFileName() {
+  ./yq -n ".xyz = 123" > test.yml
+  touch .xyz
+  
+  X=$(./yq --expression '.xyz' test.yml)
+  assertEquals "123" "$X"
+
+  X=$(./yq ea --expression '.xyz' test.yml)
+  assertEquals "123" "$X"
+
+}
+
 testBasicGitHubAction() {
   ./yq -n ".a = 123" > test.yml
   X=$(cat /dev/null | ./yq test.yml)