Here's a demo...make a file like this:

#!/bin/bash
echo "stderr" >&2
echo "stdout"

Then try these commands...

• test (both print to console)
• test | less (only shows stdout in less)
• test 2>&1 | less (redirects stderr to stdout, so both show up in less)
• test 1> /dev/null (redirects stdout to /dev/null, stderr still goes to console)
• test 2> /dev/null (redirects stderr to /dev/null, stdout still goes to console)
• test 2>&1 1> /dev/null (redirects stderr to stdout, and stdout to /dev/null. Note, this does not redirect the combined stderr/stdout you have also specified...it redirects JUST what would have been stdout)

This is making a custom file descriptor with value three . this override the bash/shell default file descriptors. and save the current stdout value you can make it 4 6..9 .do not do 5 .

exec 3>&1 

execute your command and pipe it to grep

command 2>&1 >&3 3>&- | grep word  3>&-  
#1       2   3    4   5  6   7      8

       1. your command
       2. redirect the output at the default stdout
       3. this will call the the saved value which u make for it save
       4. close file descriptor 3 for 'grep'
       5. the world famous pipe
       6. grep #man grep for details
       7. your needed words
       8. close output file descriptor 3. 

close the upper exec 3>&1 to resume work on your shell as defaults :

exec 3>&-  

Diaa Radwan 

-- MattWalsh - 28 Nov 2005