What is the point of the `yes` command?

Question

This question concerns the yes command found in UNIX and Linux machines: Basically, what is the point (if any) and history of this tool? Are there practical applications for it? Can an example be shown where it is useful in a script or chained (via pipe or redirect) with another tool?

The manpage is below:

YES(1)                    BSD General Commands Manual                   YES(1)

NAME
     yes -- be repetitively affirmative

SYNOPSIS
     yes [expletive]

DESCRIPTION
     yes outputs expletive, or, by default, ``y'', forever.

HISTORY
     The yes command appeared in 4.0BSD.

4th Berkeley Distribution        June 6, 1993        4th Berkeley Distribution

Sample output:

$ yes why
why
why
why
why
^Cwhy

Stumbled upon this when I thought I had received a "yes" dialogue but really I had be kicked out the prompt. Surprise! yes yes yes yes yes yes yes ... — Jacksonkr, Apr 06 '16 at 16:51

Joseph R. · Accepted Answer · 2013-12-22T16:38:48.633

117

It's usually used as a quick and dirty way to provide answers to an interactive script:

yes | rm -r large_directory

will not prompt you about any file being removed. Of course in the case of rm, you can always supply -f to make it steamroll the directory removal, but not all tools are so forgiving.

Update

A more relevant example of this that I recently came across is when you are fscking a filesystem and you don't want to bother answering y when prompted before fixing each error:

yes | fsck /dev/foo

edited Dec 22 '13 at 16:38

answered Nov 25 '13 at 08:22

Joseph R.

39,549

6

Does that mean that the yes output would cease once the rm is completed? – Jaryd Malbin Nov 25 '13 at 08:23
24

@JarydMalbin, yes, because that's the default behavior of SIGPIPE. – cjm Nov 25 '13 at 08:25
5

@JarydMalbin Yes it does. When rm stops reading from the pipe (read: completes), yes gets a SIGPIPE as in cjm's comment – Joseph R. Nov 25 '13 at 08:26
2

According to the manual, fsck -y /dev/foo should do the same on some file systems. Most I'd say: the manual notes exceptions for minix and cramfs. – Rolazaro Azeveires Nov 05 '16 at 11:16

score 29 · Answer 2 · edited Apr 13 '17 at 12:36

29

Beside the main point mentioned in the previous answer the yes command can also be used to test high loads of CPU on a system. yes creates a process which acts as a dummy CPU loader and results in 100% processor usage. http://en.wikipedia.org/wiki/Yes_(Unix)

edited Apr 13 '17 at 12:36

Community

1

answered Nov 25 '13 at 08:21

Vombat

12,884

nbari · Answer 3 · 2013-11-25T12:29:44.817

When updating ports on a FreeBSD workstation, using portmaster + yes becomes very handy:

yes | portmaster -da

That way you can let the machine update while you lunch and all the questions fill default to 'y,yes'

When rebuilding the world for 'make delete-old' and 'make delete-old-libs'.

this is a big time saver:

yes | make delete-old

and

yes | make delete-old-libs

Basically helps you to avoid typing / confirm certain operations that ask for a 'y' or 'yes'

What is the point of the `yes` command?

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