I was trying to extract multiple .zip files from a directory into a different folder using the unzip command. Initially, I ran `unzip /path/to/file/*.zip` while in the destination folder, but instead of unzipping the files, it just listed a "caution: filename not matched" error for each archive. After some digging online, I found out that escaping the wildcard with `unzip /path/to/file/*.zip` would work, and it did—everything got extracted where I wanted!
However, this confuses me. I thought escaping the wildcard was supposed to treat it as a regular character, likely making the command look for a file named '*.zip'. Why does this work, and what am I missing about how the command and shell work together? Also, just to note, I'm using Pop OS, which might matter.
3 Answers
When you run `unzip /path/to/file/*.zip`, the shell actually expands that wildcard to match any .zip files in the specified directory before the command gets executed. So if you had three files, it would run something like `unzip /path/to/file/a.zip /path/to/file/b.zip /path/to/file/c.zip` instead of directly calling unzip with the wildcard. Since `unzip` expects actual .zip files to be specified, you get that error message when it can't find them.
On the flip side, using `unzip /path/to/file/*.zip` prevents the shell from expanding the wildcard; it sends it as is to `unzip`, which then performs its own matching and extracts all found archives. This can be a tricky concept, but it's common for commands like `unzip` to support this kind of functionality. Normally, I'd suggest using a loop for extraction tasks, though!
Yeah! Wildcard behavior can be unintuitive, especially with different commands! Glad we figured that out.
Regarding your example with the caution message, the shell's glob patterns matched multiple files. So even though you were pointing at the archives, unzip was expecting those filenames within those archives, which is why the error popped up. Here’s a quick demo you can try to see how the commands look pre-execution after expansion!
You can also use quotes around the wildcard like this: `unzip "*.zip"`. This way, the shell also won’t expand it and will pass it directly to `unzip`. It's one of the few tools that works this way, which is handy when working with multiple zip files!
Right? There are more programs that handle it like `unzip`, though. For example, the `find` command uses similar syntax with its -name option.
Totally true! It's good practice to know when commands support this kind of wildcard expansion.
Got it! So the shell does the expansion first, that makes sense. It’s like a little lightbulb moment! Thanks for clarifying that!