Handle pipe errors more explicitly, failing at first command in the pipe was...

Handle pipe errors more explicitly, failing at first command in the pipe was OK for automation, but not very informative when ran interactively

It is SWIFT not Swift

format.sh

 #!/bin/bash
 
-# Clang software name
-clang="clang-format-5.0"
+# Clang format command, can be overridden using CLANG_FORMAT_CMD.
+# We currrently use version 5.0 so any overrides should provide that.
+clang=${CLANG_FORMAT_CMD:="clang-format-5.0"}
 
 # Formatting command
 cmd="$clang -style=file src/*.[ch] src/*/*.[ch] src/*/*/*.[ch] examples/main.c tests/*.[ch]"
@@ -10,18 +11,15 @@ cmd="$clang -style=file src/*.[ch] src/*/*.[ch] src/*/*/*.[ch] examples/main.c t
 command -v $clang > /dev/null
 if [[ $? -ne 0 ]]
 then
-    echo "Cannot find $clang"
+    echo "ERROR: cannot find $clang"
     exit 1
 fi
 
-set -e
-
-
 # Print the help
 function show_help {
-    echo -e "This script formats Swift according to Google style"
+    echo -e "This script formats SWIFT according to Google style"
     echo -e "  -h, --help \t Show this help"
-    echo -e "  -t, --test \t Test if Swift is well formatted"
+    echo -e "  -t, --test \t Test if SWIFT is well formatted"
 }
 
 # Parse arguments (based on https://stackoverflow.com/questions/192249)
@@ -53,17 +51,30 @@ done
 # Run the required commands
 if [[ $TEST -eq 1 ]]
 then
-    echo "Testing Swift formatting"
-    $cmd -output-replacements-xml | grep -c "<replacement " >/dev/null
-    res=$?
+    # Note trapping the exit status from both commands in the pipe. Also note
+    # do not use -q in grep as that closes the pipe on first match and we get
+    # a SIGPIPE error.
+    echo "Testing if SWIFT is correctly formatted"
+    $cmd -output-replacements-xml | grep "<replacement " > /dev/null
+    status=("${PIPESTATUS[@]}")
+
+    #  Trap if first command failed. Note 141 is SIGPIPE, that happens when no
+    #  output
+    if [[ ${status[0]} -ne 0 ]]
+    then
+       echo "ERROR: $clang command failed"
+       exit 1
+    fi
 
     # Check formatting
-    if [[ $res -ne 1 ]]
+    if [[ ${status[1]} -eq 0 ]]
     then
-	echo "Swift needs to be formatted"
-	exit 1
+ 	echo "ERROR: needs formatting"
+ 	exit 1
+    else
+        echo "...is correctly formatted"
     fi
 else
-    echo "Formatting Swift"
+    echo "Formatting SWIFT"
     $cmd -i
 fi