squid(8) on Linux
The text 5d8567415bfd, as Debian 9 (Stretch) shipped it.
HTTP web proxy caching server
Flags it lists
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-C -
-F -
-N -
-O -
-R -
-S -
-X -
-Y -
-a -
-d -
-f -
-h -
-i -
-l -
-n -
-r -
-s -
-u -
-v -
-z