MacBook Pro – How to Screenshot to Clipboard by Default

You can change 'Screen shot' to 'screenshot' with the following commands

defaults write com.apple.screencapture name screenshot
killall SystemUIServer

If you want to go digging a bit deeper in Terminal, you can achieve what you want by doing the following:

NOTE: Make a backup of any files you change in case you make a mistake.

1. cd /System/Library/CoreServices/SystemUIServer.app/Contents/Resources/English.lproj
2. Make a copy of the existing file:
   sudo cp ScreenCapture.strings ScreenCapture.strings.old
3. Enter Admin password if prompted
4. Convert to an editable format:
   sudo plutil -convert xml1 ScreenCapture.strings

5. sudo vi ScreenCapture.strings

   Locate the following lines:

   <key>%@ %@ at %@</key>  
   <string>%@ %@ at %@</string>  
   

   and replace with the following lines:

   <key>%@ %@ at %@</key>  
   <string>%@_%@_%@</string>  
   

6. Convert back to binary:
   sudo plutil -convert binary1 ScreenCapture.strings
7. killall SystemUIServer

which combined with the first change should get you something like this:

screenshot_2011-08-30_10.01.36.png which is very close to what you need I think

You can assign a shortcut to a script like this:

f=~/Desktop/$(date +%Y%m%d%H%M%S).png
screencapture -i $f
osascript -e 'set the clipboard to POSIX file "'$f'"'

One way to do that is to create a service in Automator:

Then give the service a keyboard shortcut from System Preferences.

If you just want to copy the path as text, replace the last line with printf %s $f | pbcopy.