Difference between printf and echo in bash

Question

What is the difference between the printf function in bash and the echo function?

Specifically, running:

echo "blah" >/dev/udp/localhost/8125

did not send the "blah" command to the server listening on 8125, whereas

printf "blah" >/dev/udp/localhost/8125

sent the data. Does printf send an extra EOF at the end of its output?

Answer 1

The difference is that echo sends a newline at the end of its output. There is no way to "send" an EOF.

Answer 2

Here is probably the best description of echo vs printf

http://www.in-ulm.de/~mascheck/various/echo+printf/

At a very high level.. printf is like echo but more formatting can be done.

Answer 3

For trivial messages (no escape sequences, no options), echo is fine. As soon as you need something more complex, you shoud use printf which is portable (i.e. behave the same regardless of the OS) and allows much better formatting, being designed from the same name C function.

Should you want to call echo in your example, the correct way would be either:

echo -n "blah" >/dev/udp/localhost/8125

or

echo "blah\c" >/dev/udp/localhost/8125

depending on the echo implementation you use.

Answer 4

echo prints its argument followed by a newline. With multiple arguments, they are separated by spaces. Depending on the unix variant, the shell and the shell options, it may also interpret some escape sequences beginning with \, and it may treat the first argument(s) as options if they start with -.

printf interprets its first argument as a format, and subsequent arguments as arguments to the % specifiers. No newline is added unless you specify one. In the first argument, all characters except two are interpreted literally: % starts a printf specifier, and \ starts an escape sequence (e.g. \n for a newline character).

Because different shells work differently, echo "$string" does not always print the specified string plus a newline. A reliable way of printing a string is printf %s "$string". If you want a newline after the string, write printf '%s\n' "$string".

In your case, assuming that blah doesn't start with a - or contain % or \, the only difference between the two commands is that echo adds a newline and printf doesn't.