I got different behaviors with the same command echo -ne "hello\n"
with bash and with dash. See below :
$ bash -c 'echo -ne "hello\n"'
hello
$ dash -c 'echo -ne "hello\n"'
-ne hello
Why is that ? I don't understand at all…
My system :
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 12.04.5 LTS
Release: 12.04
Codename: precise
The POSIX specification for echo
doesn't support any arguments. See it here.
And while the spec mentions -n
it does so to say that it is not an option and is either an implementation defined case or to be treated as a string.
So dash
is doing exactly that.
bash
, on the other hand, has non-conforming behavior in a number of ways.
This is why the use of echo
is generally discouraged in favor of the using printf
which has a much better specification and much better portable behavior.
While echo
implementation in bash
is not POSIX and Unix conformed by default, you can alter its behavior at run time or compile time.
At run time, with xpg_echo
and in POSIX mode, bash
echo
became conformant:
$ env BASHOPTS=xpg_echo SHELLOPTS=posix bash -c 'echo -ne "hello\n"'
-ne hello
or:
$ env BASHOPTS=xpg_echo POSIXLY_CORRECT= bash -c 'echo -ne "hello\n"'
-ne hello
At compile time, you can pass --enable-xpg-echo-default
and --enable-strict-posix-default
options to configure
script.
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