Unix wildcard selectors? (Asterisks)

Question

In Ryan Bates' Railscast about git, his .gitignore file contains the following line:

tmp/**/*

What is the purpose of using the double asterisks followed by an asterisk as such: **/*? Would using simply tmp/* instead of tmp/**/* not achieve the exact same result?

Googling the issue, I found an unclear IBM article about it, and I was wondering if someone could clarify the issue. Thanks!

Answer 1

It says to go into all the subdirectories below tmp, as well as just the content of tmp.

e.g. I have the following:

$ find tmp
tmp
tmp/a
tmp/a/b
tmp/a/b/file1
tmp/b
tmp/b/c
tmp/b/c/file2

matched output:

$ echo tmp/*
tmp/a tmp/b

matched output:

$ echo tmp/**/*
tmp/a tmp/a/b tmp/a/b/file1 tmp/b tmp/b/c tmp/b/c/file2

It is a default feature of zsh, to get it to work in bash 4, you perform:

shopt globstar

Answer 2

From http://blog.privateergroup.com/2010/03/gitignore-file-for-android-development/:

(kwoods)

"The double asterisk (**) is not a git thing per say, it’s really a linux / Mac shell thing.

It would match on everything including any sub folders that had been created.

You can see the effect in the shell like so:

# ls ./tmp/* = should show you the contents of ./tmp (files and folders)
# ls ./tmp/** = same as above, but it would also go into each sub-folder and show the contents there as well."