Evaluator for common shell variable expressions
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Shellvars
A Python interpreter for shell variable expressions.
shellvars supports Python 2.6 and up, and should support Jython etc as well.
The following expressions are supported:
$NAME
${NAME}
${NAME:-REPLACEMENT}
${NAME-REPLACEMENT}
${NAME:=REPLACEMENT}
${NAME=REPLACEMENT}
${NAME:?[ERRORMSG]}
${NAME?[ERRORMSG]}
${NAME:+REPLACEMENT}
${NAME+REPLACEMENT}
Recursive expressions are supported too. For instance:
>>> from shellvars import evaluate
>>> evaluate('${foo:-${bar:=baz}}', {})
('baz', {'bar': 'baz'})
For details on shell variable syntax, consult your shell or Posix documentation.
Usage
To evaluate an expression call evaluate with the expression and any variables you want available to the expression. Variables keys and values must both be strings. Variables that are missing from your variable dict are considered ‘unset’ in shell terms.
The return is an evaluated string and any variable assignments performed by the expression.
Preserving unset expressions
shellvars has a special mode where expressions that are for unset variables are preserved rather than evaluated. This permits passing them onto a real shell to interpret without needing special quoting from the user. For instance:
>>> from shellvars import SKIP
>>> evaluate('$foo $bar', {'foo': 'baz'}, absent=SKIP)
('baz $bar', {})
Installation
Use pip to install:
pip install shellvars
Development
Install the test dependencies via pip:
pip install .[test]
Push up changes as PR’s to the GitHub repository.
Bug tracker
Use the GitHub issue tracker.
Releasing
Use semver for version decisions.
To release:
Tag the repo e.g. 1.2.3
Build a signed sdist and wheel
Upload to PyPI
Copyright
Copyright (c) 2015 Robert Collins <robertc@robertcollins.net>
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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