write a custom option type to parse `-o foo,bar` and `-o +baz` etc.

[trentm]

The -H and -o options are ones used commonly (at least in illumos and my tools) for specifying columns for tabular output. One thing I'd like out of those is the ability to have a -o +baz to add the 'baz' field to the default set of columns. Similarly -o -blah to elide just that column.

Here is starter patch I have for sdcadm insts -o ...:

diff --git a/lib/cli/do_instances.js b/lib/cli/do_instances.js
index 27ae7bc..2c2123b 100644
--- a/lib/cli/do_instances.js
+++ b/lib/cli/do_instances.js
@@ -5,9 +5,10 @@
  */
 
 /*
- * Copyright (c) 2015, Joyent, Inc.
+ * Copyright (c) 2017, Joyent, Inc.
  */
 
+var assert = require('assert-plus');
 var tabula = require('tabula');
 
 var common = require('../common');
@@ -17,6 +18,10 @@ var errors = require('../errors');
  * The 'sdcadm instances (insts)' CLI subcommand.
  */
 
+
+var DEFAULT_COLUMNS = 'instance,service,hostname,version,alias';
+
+
 function do_instances(subcmd, opts, args, callback) {
     var self = this;
     if (opts.help) {
@@ -58,8 +63,33 @@ function do_instances(subcmd, opts, args, callback) {
         }
     }
 
+    assert.string(opts.o, 'opts.o');
     /* JSSTYLED */
     var columns = opts.o.trim().split(/\s*,\s*/g);
+    if (columns.length && ['+', '-'].indexOf(columns[0][0]) !== -1) {
+        // If the first char to '-o ARG' is '+' or '-', then this the fields
+        // are "relative" to the default columns.
+        //      `-o -FIELD1,FIELD2` to remove those fields from the default set
+        //      `-o -FIELD1,+FIELD2` to remove FIELD1 and add FIELD2
+        var diffs = columns;
+        /* JSSTYLED */
+        columns = DEFAULT_COLUMNS.split(/\s*,\s*/g);
+        var op; // + or -
+        diffs.forEach(function filterField(diff) {
+            if (diff[0] === '+' || diff[0] === '-') {
+                op = diff[0];
+                diff = diff.slice(1);
+            }
+            if (op === '+') {
+                if (columns.indexOf(diff) === -1) {
+                    columns.push(diff);
+                }
+            } else if (op === '-') {
+                columns.filter(function (field) { return field !== diff; });
+            }
+        });
+    }
+
     /* JSSTYLED */
     var sort = opts.s.trim().split(/\s*,\s*/g);
 
@@ -128,7 +158,7 @@ do_instances.options = [
     {
         names: ['o'],
         type: 'string',
-        default: 'instance,service,hostname,version,alias',
+        default: DEFAULT_COLUMNS,
         help: 'Specify fields (columns) to output.',
         helpArg: 'field1,...'
     },

I think this might nicely fit in a custom option. If so, do that and put it in examples... or possibly even in core dashdash. Then that could be canonical location for this to share in my tools.

[ORESoftware]

+1