Recursive globs. ** or */** globstar different on zsh, Bash, Python, and Ruby

Question

Suppose you have this directory tree:

$ tree /tmp/test
/tmp/test
├── dir_a
│   ├── dir a\012file with CR
│   ├── dir a file with spaces
│   └── sub a directory
│       └── with a file in it
├── dir_b
│   ├── dir b\012file with CR
│   └── dir b file with spaces
├── dir_c
│   ├── \012
│   ├── dir c\012file with CR and *
│   └── dir c file with space and *
├── file_1
├── file_2
└── file_3

4 directories, 11 files

(HERE is a script to produce that. The \012 is a \n to make the scripting more challenging. There is a .hidden file in there too.)

There seem to be substantial implementation differences for recursive globbing between Bash 5.1, zsh 5.8, Python pathlib 5.10, Python glob module with recursion enabled and ruby 3.0.

This also assumes shopt -s globstar with Bash and cwd is current working directory and set to /tmp/test for this example.

This is what Bash does:

1. * Just the files, directories in cwd. ie, 3 directories, 3 files
2. ** All files and directories in a tree rooted by cwd but not the cwd -- 4 and 11 files
3. **/ Only directories in the tree rooted by cwd but not including cwd -- 4 and 0
4. */** All directories in cwd and all files EXCEPT the files in cwd -- 4 and 8 files since recursion only starts in the sub directories
5. **/* Same as ** -- 4 and 11
6. **/*/ Only directories in tree -- 4 and 0 files
7. */**/* Only directories below second level and files below first -- 1 and 8

If I run this script under Bash 5.1 and zsh 5.8, they results are different:

# no shebang - execute with appropriate shell
# BTW - this is how you count the result since ls -1 ** | wc -l is incorrect 
# if the file name has \n in it.
cd /tmp/test || exit
[ -n "$BASH_VERSION" ] && shopt -s globstar
[ -n "$ZSH_VERSION" ] && setopt GLOBSTARSHORT # see table
dc=0; fc=0
for f in **; do              # the glob there is the only thing being changed
    [ -d "$f" ] && (( dc++ ))
    [ -f "$f" ] && (( fc++ ))
    printf "%d, %d \"%s\"\n" $dc $fc "$f"
done
printf "%d directories, %d files" $dc $fc

Results (expressed as X,Y for X directories and Y files for that example directory using the referenced glob. By inspection or by running these scripts you can see what is visited by the glob.):

glob	Bash	zsh	zsh GLOBSTARSHORT	pathlib	python glob	ruby
*	3,3	3,3	3,3	3,3	3,3	3,3
**	4,11	3,3	4,11	5,0‡	5,11‡	3,3
**/	4,0	4,0	4,0	5,0‡	5,0‡	5,0‡
*/**	4,8	1,7	1,8	4,0	4,8	1,7
**/*	4,11	4,11	4,11	4,12†	4,11	4,11
**/*/	4,0	4,0	4,0	4,12†	4,0	4,0
*/**/*	1,8	1,8	1,8	1,9†	1,8	1,8

‡ Directory count of 5 means the cwd is returned too.

† Python pathlib globs hidden files; the others do not.

Python script:

from pathlib import Path 
import glob 

tg="**/*"  # change this glob for testing

fc=dc=0
for fn in Path("/tmp/test").glob(tg):
    print(fn)
    if fn.is_file():
        fc=fc+1
    elif fn.is_dir():
        dc=dc+1

print(f"pathlib {dc} directories, {fc} files\n\n")      

fc=dc=0
for sfn in glob.glob(f"/tmp/test/{tg}", recursive=True):
    print(sfn)
    if Path(sfn).is_file():
        fc=fc+1
    elif Path(sfn).is_dir():
        dc=dc+1

print(f"glob.glob {dc} directories, {fc} files") 

Ruby script:

dc=fc=0
Dir.glob("/tmp/test/**/").
    each{ |f| p f; File.directory?(f) ? dc=dc+1 : (fc=fc+1 if File.file?(f)) }

puts "#{dc} directories, #{fc} files"

So the only globs that all agree on (other than the hidden file) are *, **/* and */**/*

Documentation:

1. Bash: two adjacent ‘*’s used as a single pattern will match all files and zero or more directories and subdirectories.

2. zsh: a) setopt GLOBSTARSHORT sets **.c to be equivalent to **/*.c and b) ‘**/’ is equivalent to ‘(*/)#’; note that this therefore matches files in the current directory as well as subdirectories.

3. pathlib: ** which means “this directory and all subdirectories, recursively”

4. python glob: If recursive is true, the pattern ** will match any files and zero or more directories, subdirectories and symbolic links to directories. If the pattern is followed by an os.sep or os.altsep then files will not match.

5. ruby: ** Matches directories recursively if followed by /. If this path segment contains any other characters, it is the same as the usual *.

Questions:

1. Are my assumptions about what each glob is supposed to do correct?

2. Why is Bash the only one that is recursive with **? (if you add setopt GLOBSTARSHORT to zsh the result is similar with **

3. Is it reasonable to tell yourself that **/* works for all

Answer 1

A file glob pattern works differently depending on the program doing the globing. There are many other possible programs that do globing (e.g. Perl, git, fish shell, windows’ cmd.exe, or PowerShell, csh, tcsh, tcl, etc). As you have found, specifications and behavior varies. You ask if your assumptions are correct; this is a broad question that is difficult to answer, but your research and testing looks thorough to me. That said, I don’t think it is productive to attempt to quantify and describe behavior across all of these programs, since any generalizations you discover are of limited utility. Personally, when a program says that it accepts a “glob” all I assume is that simple patterns work (a single * with text before or after), and if I need something more complex I consult specific documentation (which, sadly, is often lacking or difficult to find).

You might also find https://github.com/begin/globbing useful, since it tries to document commonly supported globbing syntax.