#

# 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()