On Wed, 13 Nov 2013 12:00:00 -0500
lingfei ouyang <oylf1...@gmail.com> wrote:

> and one more quick question?
> What is the correct way for define the variable in pre-commit hooks
> in Git bash so I can using those three variables to run git commands,
> i.e.
> git show $newrev
> git merge-base $oldreve $newrev
> since what I tried in my bash scripts first to define:
> refname="$1"
> oldrev="$2"
> newrev="$3"
> but when I run check if those three variables are valid first and it
> doesn't return any value.

Your question has little sense as is: to define a variable in bash (and
in any other POSIX shell) yo do


to assign value to a variable named "variable" (possibly creating it).
Hence a dumb answer is that you're doing assignments right.

On the other hand, I'm not so sure about these "$1", "$2" and "$3":
in a POSIX shell, $1 expands to the value of the first so-called
positional parameter, $2 to the value of the second positional
parameter and so on.  Positional parameters are arguments passed to the
shell process on its command line, for instance, if you call

$ ./myscript.sh foo bar baz

$1 inside myscript.sh would expand to foo, $2 to bar etc.

The problem is that by (stupid) default it's not an error in a POSIX
shell to attempt to expand a parameter which does not exist.
I mean, if you have a script myscript.sh reading


echo "$foo"

and run it without any arguments, like just

$ ./myscript.sh

it will execute successfully and print nothing (a newline, actually).
The reason: there was no first positional parameter, so $1 expanded to
an empty string instead of erroring out and so the variable foo has been
assigned an empty string which echo printed.

What I'm leading you to is just supposedly what you're observing is
your hook not receiving any arguments and hence it has no positional
parameters set.  Which leads us to the next question: did you read the
githooks(5) manual page to read up on how exactly Git communicates
its information to your kind of hook?  Or is there any such information
at all?  I know the answer but I want you to start thinking and doing
some active research.

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