A little more robust but still nasty (ensuring that we only hit an assignment; also notice that only the first occurrence will be replaced): perl -p -i -e 's/(?<!=)=this\|\|self/=self/'

In case anyone finds this thread, here's a function I now use in my Bash build-script:

function fix_goog_global() {
  local f=$1
  local num_to_replace
  # Nasty hack to solve goog.global not being set correctly by ClojureScript (cljs/core.cljs bottom) before being used
  # by other code (like "goog.Timer.defaultTimerObject = goog.global;" in goog/timer/timer.js).
  # Using  does not seem to be a possibility because goog/base.js is not
  # loaded as a module but with a raw "document.write('<script ..."; the imports-loader complains that the module does
  # not exist.
  # Terminate if there's any doubt that we are replacing the right thing.
  num_to_replace=$(grep -oE '[^=]=this\|\|self[,;]' "$f" | wc -l)
  if [[ "$num_to_replace" -ne 1 ]]; then
    echo "Found $num_to_replace occurences of '=this||self' to replace!"
    exit 1
  fi
  perl -p -i -e 's/(?<!=)=this\|\|self(?=[,;])/=self/' "$f"
}