How to replace environment variable value in yaml file to be parsed using python script

Question

I need to use environment variable "PATH" in yaml file which needs to be parsed with a script. This is the environment variable I have set on my terminal: $ echo $PATH /Users/abc/Downloads/tbwork This is my sample.yml: --- Top: ${PATH}/my.txt Vars: - a - b When I parse this yaml file with my script, I don't see PATH variables actual value. This is my script: import yaml import os import sys stream = open("sample.yml", "r") docs = yaml.load_all(stream) for doc in docs: for k,v in doc.items(): print k, "->", v print "\n", Output: Top -> ${PATH}/my.txt Vars -> ['a', 'b'] Expected output is: Top -> /Users/abc/Downloads/tbwork/my.txt Vars -> ['a', 'b'] Can someone help me figuring out the correct way to do it if I am doing it wrong way? JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

PY-yaml library doesn't resolve environment variables by default. You need to define an implicit resolver that will find the regex that defines an environment variable and execute a function to resolve it. You can do it through yaml.add_implicit_resolver and yaml.add_constructor. In the code below, you are defining a resolver that will match on ${ env variable } in the YAML value and calling the function path_constructor to look up the environment variable. import yaml import re import os path_matcher = re.compile(r'\$\{([^}^{]+)\}') def path_constructor(loader, node): ''' Extract the matched value, expand env variable, and replace the match ''' value = node.value match = path_matcher.match(value) env_var = match.group()[2:-1] return os.environ.get(env_var) + value[match.end():] yaml.add_implicit_resolver('!path', path_matcher) yaml.add_constructor('!path', path_constructor) data = """ env: ${VAR}/file.txt other: file.txt """ if __name__ == '__main__': p = yaml.load(data, Loader=yaml.FullLoader) print(os.environ.get('VAR')) ## /home/abc print(p['env']) ## /home/abc/file.txt Warning: Do not run this if you are not the one specifying the env variables (or any other untrusted input) as there are remote code execution vulnerabilities with FullLoader as of July 2020.