The yes command and a bit of its history

The yes command prints it’s argument repeatedly until killed. If no argument is given, it will print y until killed. It seeemed useless right? Well, not exactly. If we have a script or a command that expects an answer Yes/No to continue, we can use the yes command to provide the answer.

yes No | script or command

This is especially handy if you have to run the script repetively. Most commands today has built in capability to do this by way of -f (force) or -y option. In the absense of this, we can pipe yes into the command.

yes may sound like a simple command but it inspired a 12 pages page academic paper- The Trivial Program “yes”.

In Linux, yes is a part of coreutils. Read:

man yes
info coreutils 'yes invocation'

This is from an early man page of yes from 2.9BSD.

YES(1)              UNIX Programmer's Manual               YES(1)

NAME
     yes - be repetitively affirmative

SYNOPSIS
     yes [ expletive ]

DESCRIPTION
     Yes repeatedly outputs y, or if expletive is given, that is
     output repeatedly.  Termination is by rubout.

BUGS
     Boring.

Printed 12/7/82

The C code of yes command from 2.9BSD is quite simple.

main(argc, argv)
char **argv;
{
	for (;;)
		printf("%s\n", argc>1? argv[1]: "y");
}

A printf function in an infinite for loop that prints “y” if no command line argument is given. However, the current GNU implemenation is little more complex than this, see the source code here.