[Bash] Moved bash version detection to top and improved logic

[bkryza]

PR checklist

• Read the contribution guildelines.
• Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates)
• Filed the PR against the correct branch: master for non-breaking changes and 2.3.0 branch for breaking (non-backward compatible) changes.

Description of the PR

@wing328

I've fixed this issue (#4543) by moving the bash version detection to the top
of the generated script and improved logic to handle versions beyond 4.

I've tested it on Bash 3 and Bash 4.2:

➜  swagger-codegen git:(bugfix/4543-improve-bash-version-detection) ✗ /bin/bash output/bash/petstore-cli -h

Sorry - your Bash version is 3.2.57(1)-release

You need at least Bash 4.3 to run this script.

root@25c92892d1f6:/# /swagger/output/bash/petstore-cli -h

Sorry - your Bash version is 4.2.25(1)-release

You need at least Bash 4.3 to run this script.

Sanity to check on "4.4.0":

➜  swagger-codegen git:(bugfix/4543-improve-bash-version-detection) ✗ bash --version
GNU bash, version 4.4.0(1)-release (x86_64-apple-darwin16.0.0)
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

➜  swagger-codegen git:(bugfix/4543-improve-bash-version-detection) ✗ output/bash/petstore-cli -h

Swagger Petstore command line client (API version 1.0.0)

Usage

  petstore-cli [-h|--help] [-V|--version] [--about] [<curl-options>]
           [-ac|--accept <mime-type>] [-ct,--content-type <mime-type>]
           [--host <url>] [--dry-run] <operation> [-h|--help] [<headers>]
           [<parameters>] [<body-parameters>]

  - <url> - endpoint of the REST service without basepath
           Can also be specified in PETSTORE_HOST environment variable.
  - <curl-options> - any valid cURL options can be passed before <operation>
  - <mime-type> - either full mime-type or one of supported abbreviations:
                   (text, html, md, csv, css, rtf, json, xml, yaml, js, bin,
                    rdf, jpg, png, gif, bmp, tiff)
  - <headers> - HTTP headers can be passed in the form HEADER:VALUE
  - <parameters> - REST operation parameters can be passed in the following
                   forms:
                   * KEY=VALUE - path or query parameters
  - <body-parameters> - simple JSON body content (first level only) can be build
                        using the following arguments:
                        * KEY==VALUE - body parameters which will be added to body
                                      JSON as '{ ..., "KEY": "VALUE", ... }'
                        * KEY:=VALUE - body parameters which will be added to body
                                      JSON as '{ ..., "KEY": VALUE, ... }'

Authentication methods

  - Api-key - add 'api_key:<api-key>' after <operation>
              or export PETSTORE_API_KEY='<api-key>'
  - OAuth2 (flow: implicit)
      Authorization URL:
        * http://petstore.swagger.io/oauth/dialog
      Scopes:
        * write:pets - modify pets in your account
        * read:pets - read your pets

Operations (grouped by tags)

[pet]
  addPet             Add a new pet to the store
  deletePet          Deletes a pet
  findPetsByStatus   Finds Pets by status
  findPetsByTags     Finds Pets by tags
  getPetById         Find pet by ID
  updatePet          Update an existing pet
  updatePetWithForm  Updates a pet in the store with form data
  uploadFile         uploads an image

[store]
  deleteOrder   Delete purchase order by ID
  getInventory  Returns pet inventories by status
  getOrderById  Find purchase order by ID
  placeOrder    Place an order for a pet

[user]
  createUser                 Create user
  createUsersWithArrayInput  Creates list of users with given input array
  createUsersWithListInput   Creates list of users with given input array
  deleteUser                 Delete user
  getUserByName              Get user by user name
  loginUser                  Logs user into the system
  logoutUser                 Logs out current logged in user session
  updateUser                 Updated user

Options
  -h,--help       Print this help
  -V,--version        Print API version
  --about       Print the information about service
  --host <url>        Specify the host URL
                      (e.g. 'https://petstore.swagger.io')
  --force       Force command invocation in spite of missing
                required parameters or wrong content type
  --dry-run       Print out the cURL command without
                  executing it
  -ac,--accept <mime-type>    Set the 'Accept' header in the request
  -ct,--content-type <mime-type>  Set the 'Content-type' header in
                                  the request

[wing328]

@bkryza thanks for the enhancement 👍