Re: git hard-codes use of /bin/sh for aliases

["brian m. carlson" <sandals@crustytoothpaste.net>]

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On 2026-05-11 at 21:13:18, Thorsten Glaser wrote:
> Hi,
> 
> git aliases don’t use the user’s shell but a hardcoded /bin/sh,
> and this cannot be made configurable.
> 
> This, unfortunately, breaks quite some aliases and they cannot
> be made portable by adding something like core.sh = /bin/mksh
> to the .gitconfig.
> 
> I’d love if this could be made configurable.

Yes, I believe they use `/bin/sh`, except on Windows, where they may
look up things in the PATH.  It is very much intentional that they use
sh because it means that aliases work in a consistent way across
platforms and that they work at all.

On Linux, I have mksh, but my work machine on macOS does not, so
specifying `core.sh = /bin/mksh` would not work on all my systems.  If
you have system-level aliases as well as user-level aliases, then you
need to pick a particular shell and letting the user choose will likely
break the system-level aliases.  This is not a hypothetical: my last
company shipped system-level aliases on development VMs while users were
free to customize their user-level aliases (and shell).

This will absolutely be a problem on Windows, where you have CMD,
multiple versions of PowerShell, and bash, all with different syntax.
Some versions of PowerShell also corrupt non-Unicode data sent through
pipelines as well, which means they're effectively useless for
general-purpose scripting.

It can also lead to odd behaviour on some shells because, for instance,
zsh runs a config file with `-c`, `.zshenv`, that can make the shell
very much less POSIX compliant, so behaviour can differ substantially
from sh.

I'll also note that Git doesn't handle aliases specially.  Git has a
with-shell and a without-shell mode for running commands, and we use the
former for aliases.  We definitely do not want the with-shell mode to
generically allow arbitrary shells because we cannot handle non-POSIX
shells and will not quote correctly for them (almost certainly leading
to security vulnerabilities).  We also format the shell command as "%s
\"$@\"", which also basically requires a POSIX shell to work, and we
don't want to work around people's use of non-POSIX shells; that way
madness lies.

However, because mksh is POSIXy, you could build Git on your system with
`SHELL_PATH=/bin/mksh`, which would use `/bin/mksh` everywhere that the
shell is invoked.  That feature exists primarily for systems where `sh`
is not POSIXy or doesn't support `local` (which I know mksh does), but
there's no reason you can't use it yourself.

There has been some discussion about this issue in the past (in the
context of PowerShell) at
https://lore.kernel.org/git/CAAXzdLXt4+-34+OhS=Jn=-VeORN3Y2jMzzg9+bhyn88aN4hm0A@mail.gmail.com/ .
-- 
brian m. carlson (they/them)
Toronto, Ontario, CA

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