bash and operation on multiple files using xargs and copy

nass · 09-21-2009, 08:42 PM

Hello everyone,
I am curious about some functionality of bash...
I have a file (generated with diff) that contains only the filenames of files that do not exist in both folders (in fact it is easy since the folder with the most files contains all the files of the other folder)...

i want to back up all these files ... of course i could use any backup utility.. .but since im here to learn, i decided to do it manually...

so diff (with a suiting grep) outputs only the files that do not exist in both folders, and now i have a file that contains only the filenames of those files... no absolute path or anything.

what i tried to do to get them copied to the backup folder is the following...

cat diff_output.txt | xargs cp -vt <backup folder> <path/ to/ location/ of/ the/ extra/ files/>

and i was hoping that bash would append the filenames read in the txt file directly to the source files and proceed with the copying..
what am i doing wrong?

Thank you for your help,
Nass

slakmagik · 09-22-2009, 12:48 AM

That should work as long as you are in the directory with the files and execute

Code:

cat diff_output.txt | xargs cp -vt /path/to/<backup directory>

or preprocess the diff output to include the full path.

xargs will just append its input. If you say

Code:

cat diff_output.txt | xargs cp -vt <backup folder> <path/ to/ location/ of/ the/ extra/ files/>

and diff_output.txt contains the files 'foo' and 'bar' then cp will get

Code:

cp -vt <backup folder> <path/ to/ location/ of/ the/ extra/ files/> foo bar

You can't copy a directory onto a directory that way and foo and bar still won't exist.

nass · 09-22-2009, 04:20 AM

hm i see...
but then how does 'find' work and you can pipe its output to another command??

escaflown · 09-22-2009, 08:45 AM

Quote:

Originally Posted by nass

hm i see...
but then how does 'find' work and you can pipe its output to another command??

Check out the "-exec" option of find