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https://github.com/sayanarijit/expandvars
Expand system variables Unix style
https://github.com/sayanarijit/expandvars
bash expand python unix variables
Last synced: 3 days ago
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Expand system variables Unix style
- Host: GitHub
- URL: https://github.com/sayanarijit/expandvars
- Owner: sayanarijit
- License: mit
- Created: 2019-05-06T19:23:40.000Z (over 5 years ago)
- Default Branch: master
- Last Pushed: 2023-11-22T09:39:50.000Z (about 1 year ago)
- Last Synced: 2024-12-17T08:21:43.423Z (12 days ago)
- Topics: bash, expand, python, unix, variables
- Language: Python
- Homepage:
- Size: 101 KB
- Stars: 31
- Watchers: 4
- Forks: 9
- Open Issues: 6
-
Metadata Files:
- Readme: README.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
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README
# expandvars
Expand system variables Unix style
[](https://pypi.org/project/expandvars)
[](https://codecov.io/gh/sayanarijit/expandvars)
## Inspiration
This module is inspired by [GNU bash's variable expansion features](https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html). It can be used as an alternative to Python's [os.path.expandvars](https://docs.python.org/3/library/os.path.html#os.path.expandvars) function.
A good use case is reading config files with the flexibility of reading values from environment variables using advanced features like returning a default value if some variable is not defined.
For example:
```toml
[default]
my_secret_access_code = "${ACCESS_CODE:-default_access_code}"
my_important_variable = "${IMPORTANT_VARIABLE:?}"
my_updated_path = "$PATH:$HOME/.bin"
my_process_id = "$$"
my_nested_variable = "${!NESTED}"
```
> NOTE: Although this module copies most of the common behaviours of bash,
> it doesn't follow bash strictly. For example, it doesn't work with arrays.
## Installation
### Pip
```
pip install expandvars
```
### Conda
```
conda install -c conda-forge expandvars
```
## Usage
```python
from expandvars import expandvars
print(expandvars("$PATH:${HOME:?}/bin:${SOME_UNDEFINED_PATH:-/default/path}"))
# /bin:/sbin:/usr/bin:/usr/sbin:/home/you/bin:/default/path
```
## Examples
For now, [refer to the test cases](https://github.com/sayanarijit/expandvars/blob/master/tests) to see how it behaves.
## TIPs
### nounset=True
If you want to enable strict parsing by default, (similar to `set -u` / `set -o nounset` in bash), pass `nounset=True`.
```python
# All the variables must be defined.
expandvars("$VAR1:${VAR2}:$VAR3", nounset=True)
# Raises UnboundVariable error.
```
> NOTE: Another way is to use the `${VAR?}` or `${VAR:?}` syntax. See the examples in tests.
### EXPANDVARS_RECOVER_NULL="foo"
If you want to temporarily disable strict parsing both for `nounset=True` and the `${VAR:?}` syntax, set environment variable `EXPANDVARS_RECOVER_NULL=somevalue`.
This helps with certain use cases where you need to temporarily disable strict parsing of critical env vars, e.g. in testing environment, without modifying the code.
e.g.
```bash
EXPANDVARS_RECOVER_NULL=foo myapp --config production.ini && echo "All fine."
```
> WARNING: Try to avoid `export EXPANDVARS_RECOVER_NULL` because that will disable strict parsing permanently until you log out.
### Customization
You can customize the variable symbol and data used for the expansion by using the more general `expand` function.
```python
from expandvars import expand
print(expand("%PATH:$HOME/bin:%{SOME_UNDEFINED_PATH:-/default/path}", environ={"PATH": "/example"}, var_symbol="%"))
# /example:$HOME/bin:/default/path
```
## Contributing
To contribute, setup environment following way:
Then
```bash
# Clone repo
git clone https://github.com/sayanarijit/expandvars && cd expandvars
# Setup virtualenv
python -m venv .venv
source ./.venv/bin/activate
# Install as editable including test dependencies
pip install -e ".[tests]"
```
- Follow [general git guidelines](https://git-scm.com/book/en/v2/Distributed-Git-Contributing-to-a-Project).
- Keep it simple. Run `black .` to auto format the code.
- Test your changes locally by running `pytest` (pass `--cov --cov-report html` for browsable coverage report).
- If you are familiar with [tox](https://tox.readthedocs.io), you may want to use it for testing in different python versions.
## Alternatives
- [environs](https://github.com/sloria/environs) - simplified environment variable parsing.