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# Copyright 2013 Google Inc. All Rights Reserved.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
"""Utility for performing variable expansion in a text file.
An input template is provided on the command line. Strings of the form
${KEY_NAME} in the input will be replaced with the corresponding value for the
key provided on the command-line.
If the variable has an encoding prefix of the form ${PREFIX:KEY_NAME}, the
encoding prefix will be applied prior to emitting the variable. Currently
supported prefixes are:
A: Treat the value as a path and make it absolute.
C: C-escape the value.
Prefixes may be combined, and their order is not important.
import json
import logging
import optparse
import os
import re
import sys
_LOGGER = logging.getLogger(os.path.basename(__file__))
class Error(Exception):
"""Base class for all exceptions thrown by this module."""
def _ParseOptions():
"""Parses command-line options."""
parser = optparse.OptionParser(usage='%prog OPTIONS KEY=VALUE ...')
parser.add_option('-v', '--verbose', dest='verbose',
action='store_true', default=False,
help='Enable verbose logging.')
parser.add_option('-i', '--input', dest='input',
help='Path to the input template.')
parser.add_option('-o', '--output', dest='output',
help='Path to the output.')
(opts, args) = parser.parse_args()
opts.verbose = True
log_level = logging.INFO if opts.verbose else logging.ERROR
if not args:
parser.error('Must specify at least one key-value pair.')
if not opts.input:
parser.error('Must specify --input.')
if not opts.output:
parser.error('Must specify --output.')
if not os.path.isfile(opts.input):
parser.error('Input does not exist: %s' % opts.input)
# Parse the arguments as key-value pairs and populate a dictionary with them.
vars = {}
for arg in args:
kv = arg.split('=', 1)
if len(kv) != 2:
parser.error('Invalid key-value pair: %s' % kv)
k, v = kv
vars[k] = v
return opts, vars
def _GetVar(vars, key_match):
"""Looks up a variable (in the first group of the RE match |key_match|) and
returns its value. If the variable has a prefix specifying encoding then the
encodings are first applied before returning the value.
# Get the key.
key =
# Extract the encoding if one is specified.
enc = ''
m = re.match('^([^:]+):(.*)$', key)
if m:
enc =
key =
# Raise an error for keys that don't exist.
if key not in vars:
raise Error('The value "%s" is not defined.' % key)
# Get the value and apply any encodings.
value = vars[key]
if 'a' in enc: # Absolute path encoding.'Converting "%s" to absolute path.', key)
value = os.path.abspath(value)
if 'c' in enc: # C-style escaping.'C-escaping "%s" value.', key)
value = json.dumps(value)[1:-1]
return value
def _RewriteFile(input, output, vars):
"""Rewrites the contents of |input|, doing variable expansion with |vars|, and
writing the results to |output|.
"""'Reading input file: %s', input)
with open(input, 'rb') as input_file:
contents ='Performing variable expansion.')
f = lambda k: _GetVar(vars, k)
new_contents = re.sub('\$\{([^}]+)\}', f, contents)
if new_contents == contents:
_LOGGER.warning('Contents are unchanged.')'Writing output file: %s', output)
output_dir = os.path.dirname(os.path.abspath(output))
if not os.path.exists(output_dir):
with open(output, 'wb') as output_file:
def main():
opts, vars = _ParseOptions()
_RewriteFile(opts.input, opts.output, vars)
return 0
except Error, e:
return 1
if __name__ == '__main__':