add command line application example

examples/vulnerable_code/cla.py

@@ -0,0 +1,23 @@
+# This example is based on:
+# https://www.kevinlondon.com/2015/07/26/dangerous-python-functions.html
+#
+# Run this example from the pyt repo root directory with adapter "Every":
+# pyt -a Every examples/vulnerable_code/cla.py
+
+import subprocess
+from sys import argv
+
+def transcode_file(filename):
+    # Piping commands to the shell (shell=True) is a bad idea!
+    # What if a file name like "; rm -rf /" is provided?
+    # If the host machine runs the Python process as a privileged user,
+    # that could delete all of the files on the machine.
+    # Use quoting https://docs.python.org/2/library/pipes.html#pipes.quote (Python2) or
+    # https://docs.python.org/3.3/library/shlex.html#shlex.quote (Python3)!
+    command = 'ffmpeg -i "{source}" probably_never_existing.mp3'.format(source=filename)
+    subprocess.call(command, shell=True)
+
+# command line application intended to be called with one arg like:
+# script.py stairway_to_heaven.mp4
+if __name__ == "__main__":
+    transcode_file(argv[1:][0])