Add support for shellcheck linting.

ale_linters/sh/shellcheck.vim

@@ -0,0 +1,32 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: This file adds support for using the shellcheck linter with
+"   shell scripts.
+
+if exists('g:loaded_ale_linters_sh_shellcheck')
+    finish
+endif
+
+let g:loaded_ale_linters_sh_shellcheck = 1
+
+" This global variable can be set with a string of comma-seperated error
+" codes to exclude from shellcheck. For example:
+"
+" let g:ale_linters_sh_shellcheck_exclusions = 'SC2002,SC2004'
+if !exists('g:ale_linters_sh_shellcheck_exclusions')
+    let g:ale_linters_sh_shellcheck_exclusions = ''
+endif
+
+if g:ale_linters_sh_shellcheck_exclusions != ''
+    let s:exclude_option = '-e ' .  g:ale_linters_sh_shellcheck_exclusions
+else
+    let s:exclude_option = ''
+endif
+
+call ALEAddLinter('sh', {
+\   'name': 'shellcheck',
+\   'executable': 'shellcheck',
+\   'command': 'shellcheck ' . s:exclude_option . ' -f gcc -',
+\   'callback': 'ale#handlers#HandleGCCFormat',
+\})
+
+echo 'shellcheck' . s:exclude_option . '-f gcc -'