/bin/bash vs /bin/sh

You are on to something. Now it's 2017, using OS X Sierra, and this situation persists. Apple stopped linking the binaries. sh is a slightly larger size (and they hash to different values). It's different all over Unix and Linux with sh sometimes linking to bash. But here it's different somehow and of course, sh should be the POSIX compliant binary.

This is interesting stuff. I notice OS X has drifted far from it's BSD roots.

There aren't two binaries - sh is an alias for bash in os x. note that your third and fourth commands (where you ask for version numbers on sh and bash) both return GNU bash, version 3.2.48.

P.s. well, not literally an alias. I think sh on os x is a small executable that runs bash with a limited command set. Just trying to be clear.

There aren't two binaries - sh is an alias for bash in os x.

On my system there are two different binaries. They're both the same version of bash, but they're slightly different sizes. I don't know why. In past versions of the OS, they were hard linked. It's probably a mistake on the part of the packagers.

well, as I said in my postscript (which you probably didn't notice, granted), I'm guessing the executable you're seeing is probably a small translation thing - it handles the few syntax differences between sh and bash and passes the translated result on to bash. You'd need something like this for (say) handling some statement that's valid in bash but ought to throw an error in sh, so that someone working in sh gets the result they expect.

but that's just a guess.

re the pictures, I only have two comments:

• Concrete is not a valid substitute for common sense.
• You really need to hold a garage sale.

😝

I first noticed the difference when I started using 10.6 on my new mbp. Scripts that use /bin/sh would print echo's -e option when used. Steps to reproduce:

bash-$ /bin/sh -c 'echo -e "Hello\n\tWorld"'

-e Hello

World

bash-$ /bin/bash -c 'echo -e "Hello\n\tWorld"'

Hello

World

p.s. How you post code snippets here?

/bin/sh is suppose to be the POSIX shell, and follow explicit POSIX specificied behavior.

/bin/bash while is very close to POSIX behavior, bash does things slightly different, and bash adds new features or even changes features as the bash dev team desires.

Yes the same sources are used to build both, but the code looks at argv[0] (the name used to invoke the shell), and if it is 'sh' then bash follows POSIX rules. If the name is 'bash' it follows bash rules.

As has been suggested, it is possible to use the exact same executable and use either a Unix hardlink or a Unix symlink to the executable as a way to provide both 'sh' and 'bash' names using the same executable.

Then again, it is also possible to build the code explicitly for 'sh' and 'bash' creating separate executables. This is most likely what Mac OS X is currently doing. Then again, over the years I have seen a lot of new kids put in charge of build environments (NOT Apple's, but other companies), where these kids did not understand Unix hardlinks, symlinks, and the use of argv[0] as a way to tell the difference, so they change the build/install code which breaks the links. And it has not always been kids. My most recent pupil was nearing retirement :-)

Use the advanced editor (top-right link in the simple editor) and then use the double arrows to choose a formatting option (I think they're all the same).

All shells are different sizes for me:

-r-xr-xr-x   1 root  wheel  1371648 Jul  1 13:15 bash
-rwxr-xr-x   2 root  wheel   772992 Jul  1 13:15 csh
-r-xr-xr-x   1 root  wheel  2180736 Jul  1 13:15 ksh
-r-xr-xr-x   1 root  wheel  1371712 Jul  1 13:15 sh
-rwxr-xr-x   2 root  wheel   772992 Jul  1 13:15 tcsh
-rwxr-xr-x   1 root  wheel  1103984 Jul  1 13:15 zsh

Very interesting. I was wondering this today and knew that someone out there would be discussing it.

@BobHarris is correct. Running:

/bin/bash --posix

would (should) have the same effect as runing

/bin/sh

You can read the gospel for yourself here:http://git.savannah.gnu.org/cgit/bash.git/tree/POSIX