DOC: `input` option in `child_process.spawnSync` require `stdio[0]` to be `pipe`

[dr-js]

Affected URL(s)

https://nodejs.org/api/child_process.html#child_processspawnsynccommand-args-options

Description of the problem

to use the input option in child_process.spawnSync also need the stdio[0] option to be set as 'pipe'
current doc (v20.5.1) specifies:

input <...> The value which will be passed as stdin to the spawned process. Supplying this value will override stdio[0].

the actual behavior is more like:

Supplying this value will need stdio[0] to be 'pipe' to be overridden.

---

test done on Linux, and Win+GitBash with node v18.14.0 and v20.2.0

baseline test command:

echo "text file content" > test.txt
echo "cli content" | cat - test.txt
# will output
# > cli content
# > text file content

with nodejs input with default stdio ('pipe') works:

echo "text file content" > test.txt
node -p "String(child_process.spawnSync('cat', [ '-', 'test.txt' ], { input: 'cli content\n' }).stdout)"
# will output
# > cli content
# > text file content

but setting stdio[0] to 'ignore' or 'inherit'
will actually override input option

node -p "String(child_process.spawnSync('cat', [ '-', 'test.txt' ], { input: 'cli content\n', stdio: [ 'ignore' ] }).stdout)"
# will only output
# > text file content
node -p "String(child_process.spawnSync('cat', [ '-', 'test.txt' ], { input: 'cli content\n', stdio: [ 'inherit' ] }).stdout)"
# will wait for user input, use "Ctrl+D" to end input and see partial output

---

other execFileSync and execSync in synchronous-process-creation also have similar behavior:

# work
node -p "String(child_process.execFileSync('/usr/bin/cat', [ '-', 'test.txt' ], { input: 'cli content\n' }))"
# not work
node -p "String(child_process.execFileSync('/usr/bin/cat', [ '-', 'test.txt' ], { input: 'cli content\n', stdio: [ 'ignore' ] }))"
node -p "String(child_process.execFileSync('/usr/bin/cat', [ '-', 'test.txt' ], { input: 'cli content\n', stdio: [ 'inherit' ] }))"

# work
node -p "String(child_process.execSync('cat - test.txt', { input: 'cli content\n' }))"
# not work
node -p "String(child_process.execSync('cat - test.txt', { input: 'cli content\n', stdio: [ 'ignore' ] }))"
node -p "String(child_process.execSync('cat - test.txt', { input: 'cli content\n', stdio: [ 'inherit' ] }))"

[aduh95]

Would you like to send a PR to update the docs?

[ariel-weiss]

I'd be happy to take this one