Bash - how to unzip a piped zip file (from "wget -qO-")
Any ideas on how to unzip a piped zip file like this:
wget -qO- http://downloads.wordpress.org/plugin/akismet.2.5.3.zip
I wished to unzip the file to a directory, like we used to do with a normal file:
wget -qO- http://downloads.wordpress.org/plugin/akismet.2.5.3.zip | unzip -d ~/Desktop
Answer
The ZIP file format includes a directory (index) at the end of the archive. This directory says where, within the archive each file is located and thus allows for quick, random access, without reading the entire archive.
This would appear to pose a problem when attempting to read a ZIP archive through a pipe, in that the index is not accessed until the very end and so individual members cannot be correctly extracted until after the file has been entirely read and is no longer available. As such it appears unsurprising that most ZIP decompressors simply fail when the archive is supplied through a pipe.
The directory at the end of the archive is not the only location where file meta information is stored in the archive. In addition, individual entries also include this information in a local file header, for redundancy purposes.
Although not every ZIP decompressor will use local file headers when the index is unavailable, the tar and cpio front ends to libarchive (a.k.a. bsdtar and bsdcpio) can and will do so when reading through a pipe, meaning that the following is possible:
wget -qO- http://downloads.wordpress.org/plugin/akismet.2.5.3.zip | bsdtar -xvf- -C ~/Desktop