which is the best command to use

[lina <lina.lastname@gmail.com>]

Hi,

I have two questions, wish to get advice,

Question 1:

For a series of files:

cat  a_*.o* | grep "WARNING"

some file like a_1.o12 has WARNING, but others does not have WARNING

How can I let grep returns the filename?


Question 2:

ls . | xargs -i -t cp ./{} {}.bak

How does xargs work,

I checked google, :
-i : replace the string
-t print
but still lack well understanding,

how those xargs organise things,

and
$ ls .
a.txt b.txt

above will give a.txt.bak b.txt.bak
ls | xargs -i cp ./{} {basename {}.bak}
definitely not work,


Sorry I send it to debian list, I asked on another bash list, for two 
days the second question, no one replied. I have much more faith in this 
list.

WIth all the best regards,