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FileMaker Server – Dangers of wildcards in bash – FileMaker Today
Many web developers and some filemaker developers likely use bash while using the terminal. You may have come across some odd issues when you use a command like “rm *”, when you’re in a folder with a lot of files or a file that starts with dash. The challenge is that bash expands * to be a list of the files and folders rather than passing it on the command.
The issue with a lot of files is there’s a max command length and the issue with files that start with a dash is the command your trying to call might think your trying to pass it a argument and not a file. This feature can get fun when you use something like gnu tar.
There’s a nice write-up of the feature/issue at http://www.defensecode.com/public/DefenseCode_Unix_WildCards_Gone_Wild.txt.
$ touch -- "--checkpoint=1" $ touch -- "--checkpoint-action=exec=sh shell.sh" $ echo "whoami" > shell.sh $ touch a $ sudo tar cf archive.tar * root
What happens when you run “tar cf archive.tar *” is bash turns that into “tar cf archive.tar a –checkpoint=1 –checkpoint-action=exec=sh shell.sh shell.sh”. GNU tar tries to be as helpful as it can process each — parameter in to something it should act on regardless of where it is in the command.
The question quickly becomes “What should I do to prevent issues like this?”. For most commands there’s two methods around it. The first is prefix the * with ./ (tar cf archive.tar ./*) because that will cause bash to prefix what’s passed with ./. The second solution that works with most commands is pass — before the * (tar cf archive.tar — *) as most commands take that as a hint that everything that’s after it is a filename.