Can you please explain how $target variable is evaluated and on what the map function is applied ?

• Type the command: wmic process list full /format:csv on a windows command line to see that it produces a csv of information about the running processes.
• Wrapping that in backticks (`...`) cause perl to run that command and capture the output.
• It supplies that output one line at a time to the map: map[ (split ',', $_ )[1,24] ] `...`; which:
  1. splits it on the commas,
  2. extracts the second and 25th fields, which are the command line text and the process id respectively.
  3. And places those two fields from each line into its own anonymous array.
• Those anonymous arrays are passed into the second map (appearing lexically first in the source code):

  ... = map {
      1+ index( $_->[0] // '', $0 ) && $_->[1] != $$
      ? $_->[1]
      : ()
  } ...
  [download]

  Which tests if the first value in the anonymous array ($_->[0]) contains $0 (the name&path of the current program), and if the second value in the anonymous array ($_->[1]) (the process id) is not equal to $$ (the process id of the current perl program),

  then it passes that second value (the pid) out of the map

  otherwise it returns nothing.

• Hence, if another copy of this script is already running, $target will be assigned its pid.

I am getting syntax error

What is the text of the syntax error? What version of perl are you running?