The Problem
I sometimes need to parse a shell script to pick out variables declarations. Consider the following bash script, myscript.sh:
echo hello
server="server1.example.com"
port=8899
echo done
The Solution
The first step is read the contents of the script:
with open("myscript.sh") as stream:
contents = stream.read().strip()
print(contents)
echo hello
server="server1.example.com"
port=8899
echo done
Next, we would pick out those lines which contains the variable declaration using regular expression:
import re
var_declarations = re.findall(r"^[a-zA-Z0-9_]+=.*$", contents, flags=re.MULTILINE)
print(var_declarations)
['server="server1.example.com"', 'port=8899']
Finally, we use the csv library to parse these declarations and return a dictionary:
import csv
reader = csv.reader(var_declarations, delimiter="=")
vars = dict(reader)
print(vars)
{'server': 'server1.example.com', 'port': '8899'}
Putting it all together:
import re
import csv
def parse_bash_vars(path: str) -> dict:
"""
Parses a bash script and returns a dictionary representing the
variables declared in that script.
:param path: The path to the bash script
:return: Variables as a dictionary
"""
with open(path) as stream:
contents = stream.read().strip()
var_declarations = re.findall(r"^[a-zA-Z0-9_]+=.*$", contents, flags=re.MULTILINE)
reader = csv.reader(var_declarations, delimiter="=")
bash_vars = dict(reader)
return bash_vars
Test it out:
parse_bash_vars("myscript.sh")
{'server': 'server1.example.com', 'port': '8899'}
Conclusion
When mentioning the csv library, most thinks of it as a way to parse comma-separated-values files, but it has other uses such as parsing the bash variables or parsing /etc/os-release file.
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