Cocoa Dialog display command output and also write to log file

@May Inside the while read loop, you can do as many actions as you want, technically speaking. Just send the line info to the log file, and then on a separate line, send the "$line" to the file descriptor for cocoadialog to use.

Here's a modified version of the script above. I don't know if what you posted was only a snippet, but I didn't see a place where you specified or created the log file, so adjust what I have accordingly.

#!/bin/bash

cdPath="/Applications/Utilities/CocoaDialog.app/Contents/MacOS/CocoaDialog"

logpath="/Library/Logs/testlog.log"  ## Specifies the path to the log

## Create the log file if it's not already there
if [ ! -e "$logpath" ]; then
    touch "$logpath"
fi

## Create the name pipe input for the progressbar
rm -f /tmp/hpipe
mkfifo /tmp/hpipe
sleep 0.2

## Display indeterminate progress bar
echo "Displaying progress bar window."
"$cdPath" progressbar --indeterminate --title "Installing Apple Updates" --text "Progress..." 
--posX "right" --posY "top" --width 225 --float --icon info < /tmp/hpipe &

## Send progress through the named pipe
exec 3<> /tmp/hpipe

softwareupdate -i "$Install" | while read line; do  ## Assuming you have the $install variable specified elsewhere in the script
    echo "$line" >> "$logpath" ## We send the "line" to the log file here
    echo "10 $line" >&3    ## We send the same "line" to the file descriptor, which cocoadialog reads back
done

## Wait 1 second before shutting off progressbar
sleep 1

# Turn off progress bar by closing file descriptor 3 and removing the named pipe
echo "Closing progress bar."
exec 3>&-
rm -f /tmp/hpipe

Hope that helps.