Prevent 'cp' from outputting the file name from a bash script

Question

I have a shell script which copies a few files to the current directory, compresses them, and streams the compressed file to stdout.

On the client side I use plink to execute the script and stream stdin to a file.

This almost works.

It seems that the cp command outputs the file name being copied when its executed from inside the script. If I execute 'cp /path/to/file1 .' in the shell it does it quietly; if I execute it in a script it outputs "file1".

How do I prevent this? I've tried piping the output of the cp command to /dev/null and to a dummy text file but with no luck.

thanks for any help.

the script

#!/bin/bash cp /path/to/file1 . cp /path/to/file2 . cp /path/to/file3 . tar -cvzf package.tgz file1 file2 file3 cat package.tgz

the output

file1 file2 file3 <<binary data>>

If you want the tar output, why not removing the -f package.tgz and letting tar print it directly to stdout? — CesarB
– CesarB, Commented Nov 7, 2008 at 1:15
@Ken G: and remove the cat package.tgz at the end, of course. — CesarB
– CesarB, Commented Nov 7, 2008 at 1:28

CesarB · Accepted Answer · 2008-11-07 01:06:20Z

19

It's not cp, it's tar. You are passing it -v, which makes it print the names of the files.

answered Nov 7, 2008 at 1:06

CesarB

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Comments

bendin · Accepted Answer · 2008-11-07 05:55:06Z

Aha! I'd always assumed that the file names emitted by tar go to stderr, but that isn't always the case: only if you write your tar file to stdout do the files written by -v go to stderr:

$ tar cvf - share > /dev/null share/ # this must be going share/.DS_Store # to stderr since we share/man/ # redirected stdout to share/man/.DS_Store # /dev/null above. share/man/man1/ share/man/man1/diffmerge.man1

The counter-example:

$ tar cvf blah.tar share > /dev/null

This produced no list of file names because they got sent to /dev/null. I guess you learn something new every day. :-)

bigendian · Accepted Answer · 2011-11-12 03:33:39Z

As others pointed out, the -v (verbose) option to tar is kicking out the file names to STDERR. You can also make your script more efficient by having tar write the compressed file stream to STDOUT:

tar zcf - file1 file2 file3

In this example, the "-" option passed as the filename makes tar write the output to STDOUT.

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