How to check for an exploding zip file in bash?

Question

I have a bash shell script that unzips a zip file, and manipulates the resulting files. Because of the process, I expect all the content I am interested to be within a single folder like so:

file.zip  
  /file  
    /contentFolder1
    /contentFolder2
    stuff1.txt
    stuff2.txt
    ...

I've noticed users on Windows typically don't create a sub folder but instead submit an exploding zip file that looks like:

file.zip  
    /contentFolder1
    /contentFolder2
    stuff1.txt
    stuff2.txt
    ...

How can I detect these exploding zips, so that I may handle them accordingly? Is it possible without unzipping the file first?

Answer 1

I wouldn't try to detect it. I'd just force unzip to do what I want. With InfoZip:

$ unzip -j -d unzip-output-dir FileFromUntrustedSource.zip

-j makes it ignore any directory structure within the file, and -d tells it to put files in a particular directory, creating it if necessary.

If there are two files with the same name but in different subdirectories, the above command will make unzip ask if you want to overwrite the first with the second. You can add -o to force it to overwrite without asking, or -f to only overwrite if the second file is newer.

Answer 2

Unzip to a directory first, and then remove the extra layer if the zip is not a bomb.

tempdir=`mktemp -d`
unzip -d $tempdir file.zip
if [ $(ls $tempdir | wc -l) = 1 ]; then
        mv $tempdir/* .
        rmdir $tempdir
else
        mv $tempdir file
fi

Answer 3

If you want to check, unzip -l will print the contents of the zip file without extracting them. You'll have to massage the output a bit, though, since it's printing all sorts of additional crud.