bash-as-sh echo -n

Question

Is there a way to get bash (version 3.2.57(1), if it matters), in the mode where it's emulating sh, to implement the -n option to the echo builtin?

Specifically, I'm curious whether there might be one option I could set somewhere, rather than seeking out and rewriting N calls to echo -n in M different scripts, that had — perhaps only by dumb luck — been working fine for years. Clearly it's possible for bash's echo builtin to implement -n, because in full bash mode, it does.

[Disclaimer: Yes, I know that echo -n is not portable in the first place, and that printf is recommended.]

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Side note: Commentators have noted that this version of bash is "17 years old". Someone should tell Apple about this — it's the version that came with MacOS Ventura 13.0 on the reasonably new Mac where I'm typing this.

Answer 1

The best idea I could come up with is replacing the builtin echo with the "real" echo executable from the GNU coreutils, that is almost certainly installed if you have a bash:

echo() { "$(type -P echo)" "$@" ; }

which simply shadows the built-in.

Since GNU Coreutil's echo.c really isn't very long, and a good part of that is special-case handling for things like "am I running on UNIX System V and am expected to behave like that?", --help printing and similar things you don't strictly need, you might consider just including a small C implementation of echo in your shell scripts and put it through the POSIX-specified c99 if you know that you got that. Heck, this is a machine from the 2000s, so you might as well assume you have perl and implement the same in perl.

Answer 2

As seen at Why is printf better than echo?, bash doesn't support the -n option (nor -e/-E) when both the posix option is enabled (like when invoked as sh) and the xpg_echo option is enabled (as it is by default on systems where bash is built so as to be UNIX compliant).

So to have bash's echo support -n (and -e/-E and combinations thereof like echo -en, echo -e -n...), you need to disable either or both of those options. If you want that sh to still be UNIX-compliant except for that -n, it's probably xpg_echo only that you want to turn off:

shopt -u xpg_echo

Example:

$ bash -o posix -O xpg_echo -c 'echo -n a'
-n a
$ bash -o posix -O xpg_echo -c 'shopt -u xpg_echo; echo -n a'
a

bash is still mostly UNIX-compliant, except for the -n that was not printed.

$ bash -o posix -O xpg_echo -c 'set +o posix; echo -n a'
a

That -n handling is enabled, but also some other non-UNIX compliances so it behaves even less like standard sh.

Answer 3

You can define a function with the necessary functionality

echo() ( IFS=' ' nl='\n'; [ "$1" = '-n' ] && shift && nl=; printf "%s$nl" "$*" )

In dash (admittedly not bash in sh mode, and definitely not the version you have), this avoids external references.

Note that POSIX says the only guaranteed compatible way to use echo is without arguments or backslash escapes:

If the first operand is -n, or if any of the operands contain a <backslash> character, the results are implementation-defined.

If you want the extended version that handles backslash escapes, use %b instead of %s:

echo() ( IFS=' ' nl='\n'; [ "$1" = '-n' ] && shift && nl=; printf "%b$nl" "$*" )

Answer 4

The external /bin/echo on my Mac does support -n, and you can disable the Bash builtin one with enable -n:

bash-3.2$ enable -n echo
bash-3.2$ type echo
echo is /bin/echo
bash-3.2$ echo -n foo |od -c
0000000    f   o   o
0000003

Answer 5

Fix the Underlying Issue

Google will return a plethora of results if you use "Upgrade bash macOS" as the search term. Using a native exchange answer, and combining 2 answers into one (Per your Side note):

Frequently Asked Questions about the GNU Licenses: Tivoization

When people distribute User Products that include software under GPLv3, section 6 requires that they provide you with information necessary to modify that software. User Products is a term specially defined in the license; examples of User Products include portable music players, digital video recorders, and home security systems.

Since Apple's Darwin OS has been closed source since about 10.5, providing an upgraded BASH would violate the above paragraph, so Apple does know. There is a way to update the BASH shell and even make it the default:

Install Updated Bash Via Homebrew

Paste the following in your terminal:

1. /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" as one line.
2. Issue brew install bash

This should install an updated version of BASH in Homebrew which is then symlinked. Use which bash to find the location To set this as the default:

1. Edit /etc/shells.
2. Add the path + the binary to the file at the end.
3. Logout and back in to update your environment.
4. Use the chsh command to "Change Shells", providing the path to the new BASH version. This should make the new version your default shell.

Sources

• AskDifferent: Update bash to version 4.0 on OSX
• Homebrew: The Missing Package Manager for MacOS

Answer 6

On the macOS 14.3 version of bash, unsetting posix seems to be enough:

% /bin/sh -c 'set +o posix; echo -n foo; set -o posix; echo -n bar'
foo-n bar
% /bin/sh --version
GNU bash, version 3.2.57(1)-release (arm64-apple-darwin23)
Copyright (C) 2007 Free Software Foundation, Inc.