Hi,
In Shell script, what will be the output of the command $! , $_ and $$ ?

Thanks

They are not commands, they are special shell variables.

• $! the process id of the last command run in the background.
  
• $- the current options supplied to this invocation of the shell.
  
• $_ Last argument of previous command
  
• $$ the process number of this shell - useful for including in filenames, to make them unique.

Use the echo command to see what they contain.

Mike

I just would like to add something to $$: do not rely on a really unique file name using $$. For anything bordering on important things, additional checks will be needed.