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doc,test: specify and test CLI option precedence rules
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Refs: #35098 (comment)

PR-URL: #35106
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
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addaleax committed Sep 22, 2020
1 parent 255d47a commit b47172d
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6 changes: 6 additions & 0 deletions doc/api/cli.md
Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,11 @@ dashes (`-`) or underscores (`_`).

For example, `--pending-deprecation` is equivalent to `--pending_deprecation`.

If an option that takes a single value, for example `--max-http-header-size`,
is passed more than once, then the last passed value will be used. Options
from the command line take precedence over options passed through the
[`NODE_OPTIONS`][] environment variable.

### `-`
<!-- YAML
added: v8.0.0
Expand Down Expand Up @@ -1487,6 +1492,7 @@ $ node --max-old-space-size=1536 index.js
[`--openssl-config`]: #cli_openssl_config_file
[`Buffer`]: buffer.html#buffer_class_buffer
[`SlowBuffer`]: buffer.html#buffer_class_slowbuffer
[`NODE_OPTIONS`]: #cli_node_options_options
[`process.setUncaughtExceptionCaptureCallback()`]: process.html#process_process_setuncaughtexceptioncapturecallback_fn
[`tls.DEFAULT_MAX_VERSION`]: tls.html#tls_tls_default_max_version
[`tls.DEFAULT_MIN_VERSION`]: tls.html#tls_tls_default_min_version
Expand Down
22 changes: 22 additions & 0 deletions test/parallel/test-cli-options-precedence.js
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@@ -0,0 +1,22 @@
'use strict';
require('../common');
const assert = require('assert');
const { spawnSync } = require('child_process');

// The last option on the command line takes precedence:
assert.strictEqual(spawnSync(process.execPath, [
'--max-http-header-size=1234',
'--max-http-header-size=5678',
'-p', 'http.maxHeaderSize'
], {
encoding: 'utf8'
}).stdout.trim(), '5678');

// The command line takes precedence over NODE_OPTIONS:
assert.strictEqual(spawnSync(process.execPath, [
'--max-http-header-size=5678',
'-p', 'http.maxHeaderSize'
], {
encoding: 'utf8',
env: { ...process.env, NODE_OPTIONS: '--max-http-header-size=1234' }
}).stdout.trim(), '5678');

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