Trace Macro Expansion of Type or Function

trace_macro.sh

#!/bin/bash

# Use as `./macro.sh $CC $HEADER $MACRO`, where CC is the 
# C or C++ compiler desired. There must be an arg1, arg2, 
# arg3, and, or the script will quit.

if [ "$#" -ne 3 ]; then
    echo "Use: ./.sh.sh \$CC \$HEADER \$MACRO."
    echo "Must invoke with exactly 3 args."
    exit 1
fi

echo | $1 -E -xc -include $2 - | grep $3