/ShellArgparser

A shell argparse tool based on python argparse module.

Primary LanguagePythonMIT LicenseMIT

ShellArgparser

A shell argparse tool based on python argparse module.

Install

  1. python >= 3 is required;
  2. Download the script parseopt.py to any of your directory.

Usage

In the shell script, add parser information as in python. e.g.

python-styled parser

...
parser.add_argument("input", type=str, help="Input file.")
parser.add_argument("-o", "--output", type=str, default="${input}_out", 
    help="Output file. Default: <input>_out")

shell parser test.sh

<<"PARSER"
("input", type=str, help="Input file.")
("-o", "--output", type=str, default="${input}_out",
    help="Output file. Default: <input>_out")
PARSER
opts=$(python parseopt.py $0 $*) && eval $opts || exit 1

Now have a try

$ bash test.sh
usage: test.sh [-h] [-o OUTPUT] input
test.sh: error: the following arguments are required: input

$ bash test.sh -h
usage: test.sh [-h] [-o OUTPUT] input

positional arguments:
  input                 Input file.

optional arguments:
  -h, --help            show this help message and exit
  -o OUTPUT, --output OUTPUT
                        Output file. Default: <input>_out

Interpretation of shell parser

Just in case if you're interested in the implementation. Here is the process

  1. $(python parseopt.py $0 $*) command run the python script in the shell script, $0 is the name of the script (test.sh here); $* indicate all arguments passed to test.sh (such as -h)
  2. In parseopt.py, the program searches for control flags <<"PARSER" and PARSER, which represent the start and the end of argument parser respectively, and return the wrapped content to the next step.
  3. The program searches bracket pairs () to get the argument parser string. Python interpreter function eval is used to resolve the strings and build the parser.
  4. Then all arguments (passed by $*) are resolved by the parser, which tells if there is any missing positional argument, unknown option or -h, --help.
  5. If no error is raised at step 4, the python script writes arguments and their values to the sys.stdout as 
    export input=<input>; export output=<output>; ...
    which is then assigned to shell variable $opts
  6. eval $opts in shell scripts sets up all the arguments, so them can be used in following lines.