Two potential bugs in aliases that expand to shell commands

Two potential bugs in aliases that expand to shell commands

[Han]

These might just be documentation bugs.

Aliases that expand to shell commands are only documented fairly
superficially, but `git help config` does say: "If the alias expansion
is prefixed with an exclamation point, it will be treated as a shell
command."

It also says, nearer the beginning: "String values may be entirely or
partially enclosed in double quotes. You need to enclose variable
values in double quotes if you want to preserve leading or trailing
whitespace, or if the variable value contains comment characters (i.e.
it contains # or ;)."

There appears to be another case string values need to be enclosed in
quotes, which is a shell command where you want to preserve quote
characters (not leading or trailing); a minimal example is

  shortcut = !cd "" && pwd

will act like you ran, in bash,

$ cd  && pwd

and print your homedir path, whereas

  shortcut = !"cd \"\" && pwd"

will act like you ran, in bash,

$ cd "" && pwd

and stay in the top-level directory of the repo (which is where
aliases that expand to shell commands are run from).

This is problematic precisely because aliases that expand to shell
commands are run from the top-level directory of the repo: if you had
an alias that worked great at the top-level directory, like

  shortcut = !do_something

but it was doing the wrong thing in subdirectories, my first instinct,
at least, upon reading "Note that shell commands will be executed from
the top-level directory of a repository, which may not necessarily be
the current directory. GIT_PREFIX is set as returned by running git
rev-parse --show-prefix from the original current directory.", is to
do

  shortcut = !cd "$GIT_PREFIX" && do_something

which will now do the right thing in subdirectories, but at the
top-level directory of the repo, $GIT_PREFIX is undefined/the empty
string, and it cds to your homedir.

The other bug I'm much more confused by. If you have an alias like

  shortcut = !"echo -n lol; echo wut"

it will, in fact, print

-n lol
wut

which is, uh, not what bash prints. Is git special-casing echo?

(I discovered these while adding something semi-jokingly to my
.gitconfig: https://github.com/laughinghan/dotfiles/commit/34f5528825b287ff40acfe57808b32931a87261c
)

Han

Re: Two potential bugs in aliases that expand to shell commands

[Jeff King]

On Wed, Apr 03, 2013 at 07:05:33PM -0700, Han wrote:

> There appears to be another case string values need to be enclosed in
> quotes, which is a shell command where you want to preserve quote
> characters (not leading or trailing); a minimal example is
> 
>   shortcut = !cd "" && pwd

Yes. You must escape any double-quotes that are not the beginning or
end of a quoted string.

>   shortcut = !"cd \"\" && pwd"

This is fine. Technically so is:

  shortcut = !cd \"\" && pwd

but I think it is more readable to put such shell snippets inside a
double-quoted string, to make it more clear what is going on.

Documentation patches welcome.

> The other bug I'm much more confused by. If you have an alias like
> 
>   shortcut = !"echo -n lol; echo wut"
> 
> it will, in fact, print
> 
> -n lol
> wut
> 
> which is, uh, not what bash prints. Is git special-casing echo?

No, git does not special-case echo. But it runs shell commands with
/bin/sh, which may or may not be bash on your system (and "-n" is not
necessarily portable to other POSIX shells).

If you really want to use bash, do:

  shortcut = "!bash -c 'echo -n lol; echo wut'"

or just use printf, which is a portable way to spell "echo -n".

-Peff