## Variable substitution. Variables are $delimited$#import re error = 'varsubst.error' class Varsubst:    def __init__(self, dict):        self.dict = dict        self.prog = re.compile('\$([a-zA-Z0-9_]*)\$')        self.do_useindent = 0     def useindent(self, onoff):        self.do_useindent = onoff     def subst(self, s):        rv = ''        while 1:            m = self.prog.search(s)            if not m:                return rv + s            rv = rv + s[:m.start()]            s = s[m.end():]            if m.end() - m.start() == 2:                # Escaped dollar                rv = rv + '$'                s = s[2:]                continue            name = m.group(1)            if not self.dict.has_key(name):                raise error, 'No such variable: '+name            value = self.dict[name]            if self.do_useindent and '\n' in value:                value = self._modindent(value, rv)            rv = rv + value     def _modindent(self, value, old):        lastnl = old.rfind('\n', 0) + 1        lastnl = len(old) - lastnl        sub = '\n' + (' '*lastnl)        return re.sub('\n', sub, value) def _test():    import sys    import os     sys.stderr.write('-- Copying stdin to stdout with environment map --\n')    c = Varsubst(os.environ)    c.useindent(1)    d = sys.stdin.read()    sys.stdout.write(c.subst(d))    sys.exit(1) if __name__ == '__main__':    _test()