I'm downloading a file and then unzipping it from a Bash script file.
#!/bin/sh wget -N http://example.com/file.zip unzip -o file.zip Is there a way to check if wget actually downloaded a new file? For instance, if the remote version of file.zip is the same as the local version it will not retrieve the file. I only want to unzip the file if wget actually retrieves a new file.
You should check return value and output from wget to figure out whether file has been downloaded:
out=$(wget -qN 'http://example.com/file.zip' 2>&1) [[ $? -eq 0 && $out ]] && unzip file.zip If file.zip is already there with same timestamp then wget will not download it and nothing will be written to stdout/stderr making out variable empty.
[[ not found means you're not using bash. Make sure to use bash when you run this. To display output you can add echo "$out" after first line.Don't use the Last-Modified header, that's dependent on the server. Anubhava@'s also works but this is less overhead and slightly more portable between Bourne shell variations:
This gets you what you need:
wget -N http://example.com/file.zip 2>&1 | grep "not retrieving" 2>&1 > /dev/null || unzip file.zip It's essentially saying this, with more detail added for readability:
out=$(wget -N http://example.com/file.zip 2>&1) if [ $(echo $(out) | grep "not retrieving") ]; then echo "No new file; not unzipping" else unzip file.zip fi It's an old question but don't work anymore. I don't have any return when I set the quiet option of wget in the 2 case but we can have the HTML Code with the -S option of wget.
-200 if the file is downloaded
-304 if is the same file
-others... for all "bad" situations
a solution without change the @anubhava method's :
out=$(wget -SN 'http://example.com/file.zip' 2>&1 | grep "HTTP/" | awk '{print $2}') [[ $out -eq 200 ]] && unzip file.zip You can use
curl -I http://example.com/file.zip and check Last-Modified: value.
You may also use wget --timestamping but requesting HEAD info you have more control.
curlandwgetcan be told not to download a file if it hasn't changed. See stackoverflow.com/q/32322456/258523 for a recent question and answer about this forwget.