Simulating ENTER keypress in bash script

Question

I've created a really simple bash script that runs a few commands. one of these commands needs user input during runtime. i.e it asks the user "do you want to blah blah blah?", I want to simply send an enter keypress to this so that the script will be completely automated.

I won't have to wait for the input or anything during runtime, its enough to just send the keypress and the input buffer will handle the rest.

If the tool you are trying to automate is `apt-get`, the proper solution is to preseed the debconf database with your preferred values; then it won't ask you. — tripleee, Mar 04 '15 at 05:20

Tilman Vogel · Accepted Answer · 2022-10-28T08:37:15.937

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echo -ne '\n' | <yourfinecommandhere>

or taking advantage of the implicit newline that echo generates (thanks Marcin)

echo | <yourfinecommandhere>

edited Oct 28 '22 at 08:37

answered Jun 07 '11 at 11:39

Tilman Vogel

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if you feed this output to `xxd` you get `5c6e` hex, which is a literal `\n`. if you do just `echo | xxd` you actually end up with a hex of `0a`. So I guess use whichever your program needs. – Marcin Jun 07 '11 at 11:46
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@Marcin, I am surprised, I get `0a0a` which is still not as intended, adding an `-n` suppreses the implicit newline. But your are of course right, a plain `echo | ...` works fine here. Will update my answer. – Tilman Vogel Jun 07 '11 at 11:49
Heh, it didn't look quite right to me, so I had to feed it through xxd. It's by far the simplest yet efficient method of seeing exactly what commands output. Gotta love stupid Unix tricks. – Marcin Jun 07 '11 at 11:55
@Marcin, still, why do you get `5c6e`? Did you omit the `-e` or does your shell or `echo` not treat that option? – Tilman Vogel Jun 07 '11 at 12:00
i get: `echo -ne "\n" | xxd 0000000: 0a` and `echo -n "\n" | xxd 0000000: 5c6e` and `echo "\n" | xxd 0000000: 5c6e 0a` I have not seen any difference between single and double quotes. My shell is just a regular bash, is there settings that would regulate behavior of such basic functionality? – Marcin Jun 07 '11 at 12:09
@Marcin, your last findings are all as I would expect. Also, back-slash is only treated special in double-quotes for dollar, back-tick, double-quote, backslash and newline according to `man bash`, so that's fine too. I was puzzled by your original comment stating that `echo -e '\n' | xxd` would output `0000000: 5c6e`. Can you still reproduce this? – Tilman Vogel Jun 07 '11 at 14:36
Is it portable on OSX? – David Froger Dec 09 '16 at 14:31
The behaviour of `echo` is highly dependent on your shell and system, it varies quite a lot actually (which explains some of the comments). The only thing that is guaranteed to work is `echo "string without escape characters"`. There is no need to add this part to your answer, as `echo | cmd` is exactly the same. I recommend you edit it out (if you *do* want an explicit newline echo, then `printf '\n'` is the portable way to do that). – Martin Tournoij Sep 18 '17 at 10:39
@TilmanVogel How to chain this? I would like to press multiple enters after running `mycommand`. – Sunlight Oct 27 '22 at 06:04
@Sunlight What do you mean by "after running"? If you want to feed multiple enters to the same program, you can easily do `echo -ne '\n\n\n' | ` to feed it three enters. If you need an indefinite number of enters, use `yes` as suggested by some of the other answers. – Tilman Vogel Oct 28 '22 at 08:44

score 53 · Answer 2 · edited Aug 31 '16 at 19:42

53

You can just use yes.

# yes "" | someCommand

edited Aug 31 '16 at 19:42

Paul Roub

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answered Aug 31 '16 at 19:18

David Hamner

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score 52 · Answer 3 · answered Jun 07 '11 at 11:41

52

You might find the yes command useful.

See man yes

answered Jun 07 '11 at 11:41

pavium

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`yes` I do find it useful. – AncientSwordRage Sep 05 '12 at 23:03
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This simulates pressing "y" repeatedly rather than the Enter key. While this is probably what you want to yes/no questions, it won't work for anything that doesn't expect a "y". – Burhan Ali Jul 21 '15 at 14:51
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@BurhanAli: you can change what `yes` sends as its output. Read the man page. – siride Apr 21 '17 at 15:21
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can I send yes mutiple times for a script that expects default values [value] {enter} – AK_ Jun 11 '18 at 21:26
This only works for things like yum. Where that string is expected. – eco Apr 08 '19 at 19:09

score 25 · Answer 4 · answered Apr 11 '16 at 08:30

25

Here is sample usage using expect:

#!/usr/bin/expect
set timeout 360
spawn my_command # Replace with your command.
expect "Do you want to continue?" { send "\r" }

Check: man expect for further information.

answered Apr 11 '16 at 08:30

kenorb

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especially helpful if multiple enter keypresses need to be sent – Andy Jul 28 '18 at 20:11
This is the best way, specially for things like phars where different stdout and stdin strings are sent. – eco Apr 08 '19 at 19:09
Also remember to just enter my_command arg if you have an argument. – eco Apr 08 '19 at 21:18
It always says: invalid command name "my_command", even when command is simple like "ls". – taranaki Jun 05 '22 at 04:49

score 11 · Answer 5 · answered Jun 07 '11 at 11:41

11

You could make use of expect (man expect comes with examples).

answered Jun 07 '11 at 11:41

barti_ddu

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Bocar · Answer 6 · 2021-12-27T18:48:11.087

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I know this is old but hopefully, someone will find this helpful.

If you have multiple user inputs that need to be handled you can use process substitution and use echo as a 'file' for cat with whatever is needed to handle the first input like this:

# cat ignores stdin if it has a file to look at
cat <(echo "selection here") | command

and then you can handle subsequent inputs by piping the yes command with the answer:

 cat <(echo "selection here") | yes 'y' | command

edited Dec 27 '21 at 18:48

answered Dec 27 '21 at 15:13

Bocar

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just what I needed thanks. I'm generating 12 different NestJs modules and each command has two prompts. – LeanKhan Mar 11 '22 at 20:37

Simulating ENTER keypress in bash script

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