Also accept grammar from stdin

entrypoint.sh

@@ -2,8 +2,15 @@
 #
 # Entrypoint for the xle Docker image.
 # 
-# - /grammar.lfg contains the grammar
-# - $1 contains the sentence to be parsed (passed as parameter)
+# You need to provide the following information:
+# 1. A sentence to parse as first (and only) command line argument ($1)
+# 2. A grammar to parse with. The grammar is searched first at /grammar.lfg. If no such file exists, the grammar is read from stdin.
+
+if [[ ! -f /grammar.lfg ]]
+then
+    # Use "cat" to read everything stdin has to offer and then use Bash to write it to a file
+    cat > /grammar.lfg
+fi
 
 # Write xlerc containing instructions to parse
 echo "create-parser /grammar.lfg" > xlerc