How to filter files when using scp to copy dir recursively?

Question

I need to copy all the .class files from server to local with all dir reserved. e.g. server:/usr/some/unknown/number/of/sub/folders/me.class will be /usr/proj

Answer 1

Since you can scp you should be ok to ssh,
either script the following or login and execute...

# After reaching the server of interest
cd /usr/some/unknown/number/of/sub/folders
tar cfj pack.tar.bz2 $(find . -type f -name *.class)

return back (logout) to local server and scp,

# from the local machine
cd /usr/project/backup/some/unknown/number/of/sub/folders
scp you@server:/usr/some/unknown/number/of/sub/folders/pack.tar.bz2 .
tar xfj pack.tar.bz2

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If you find the $(find ...) is too long for your tar change to,

find . -type f -name *.class | xargs tar cfj pack.tar.bz2

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Finally, since you are keeping it in /usr/project/backup/,
why bother extraction? Just keep the tar.bz2, with maybe a date+time stamp.