[PATCH v4 2/3] Documentation: alias: add notes on shell expansion

Ian Wienand
2024-05-24T07:34:32Z

When writing inline shell for shell-expansion aliases (i.e. prefixed
with "!"), there are some caveats around argument parsing to be aware
of. This series of notes attempts to explain what is happening more
clearly.

Signed-off-by: Ian Wienand <iwienand@redhat.com>
---
Documentation/config/alias.txt | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)

diff --git a/Documentation/config/alias.txt b/Documentation/config/alias.txt
index 40851ef429..51fa876c91 100644
--- a/Documentation/config/alias.txt
+++ b/Documentation/config/alias.txt
@@ -27,3 +27,24 @@ it will be treated as a shell command. For example, defining
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. See linkgit:git-rev-parse[1].
+* If the shell alias is the full path to a binary, it will be executed
+ directly with any arguments.
+* If the alias contains any whitespace or reserved characters, it will
+ be considered an inline script and run as an argument to `sh -c`.
+* When running as a script, Git appends "$@" to the alias shell
+ command when arguments are present. If there are no arguments,
+ `"$@"` will not be appended.
+** This may initially be confusing if your alias script references
+ argument variables, or is otherwise not expecting the presence of
+ `"$@"`. For example: `alias.echo = "!echo $1"` when run as `git
+ echo arg` will actually execute `sh -c "echo $1 $@" "echo $1"
+ "arg"` resulting in output `arg arg`. An alias `alias.for = "!for
+ i in 1 2 3; do echo $i; done"` will fail if any arguments are
+ specified to `git for` as the appended `"$@"` will create invalid
+ shell syntax.
+** A convenient way to deal with this is to write your script
+ operations in an inline function that is then called with any
+ arguments from the command-line. For example `alias.echo = "!e() {
+ echo $* ; }; e" will work as expected, with the function `e`
+ receiving any arugments from the command-line.
+** Setting `GIT_TRACE=1` can help debug the command being run.
--
2.45.1