def TeXLaTeXStrFunction(target = None, source= None, env=None):
    """A strfunction for TeX and LaTeX that scans the source file to
    decide the "flavor" of the source and then returns the appropriate
    command string."""
    if env.GetOption("no_exec"):

        # find these paths for use in is_LaTeX to search for included files
        basedir = os.path.split(str(source[0]))[0]
        abspath = os.path.abspath(basedir)

        if is_LaTeX(source,env,abspath):
            result = env.subst('$LATEXCOM',0,target,source)+" ..."
        else:
            result = env.subst("$TEXCOM",0,target,source)+" ..."
    else:
        result = ''
    return result