Remove GNU sed prerequisite

README.md

@@ -19,7 +19,6 @@ will be faded away.
 0. dot - graphviz version 2.41.20190308.1641 (20190308.1641)
 	* new versions should work, if not I will fix it
 	* lower versions may work, but not tested yet, I am lazy...
-1. GNU sed, if you don't have one, modify the build script to fit the purpose
 
 ### usage
 

build_call_graph.sh

@@ -44,8 +44,16 @@ else
 fi
 
 # echo ${out}
+which dot > /dev/null
+if [ $? -ne 0 ]; then
+	echo "no graphviz dot found"
+	exit -1
+fi
 
 dot -Tsvg -o ${out} ${src} > /dev/null
-sed -ri 's#</svg>##' ${out}
+
+sed -i.bak 's#</svg>##' ${out}
+rm -f ${out}.bak
+
 cat "${attach}" >> ${out}
 echo "</svg>" >> ${out}