Fix bug in tools/cat bash script

src/tools/cat

@@ -2,11 +2,16 @@
 
 files=$1
 
-if [ -e $files ]
-then
+# Make target file empty
 cat /dev/null > $2
+
+# Attach each file from the specified mask to the target file
 for file in $files
 do
+    # Process a file only if it exists
+    if [ -e $file ]
+    then
+        # Append content of the current file to the target file
         cat $file >> $2
-    done
     fi
+done