Hi Ken, Follow up on test results for the 3 scenarios. I added the OS mem usage in each case (which is the real issue). The last option seems to be a little faster ( <$fh> ) but mem usage is similar to Memory::Usage shows. I am going to try the 'slurp string' as the next option as suggested by BrowserUK. Also interesting that using the reference (T2) uses 15% more RAM.

T1: size(\@data):          177490392  total_size(\@data):    183760484
+8
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 6569 xxxxxxx   25   0 6355m 6.0g 1592 R 100.0 51.5   0:46.67 perl


T2: size($data_ref):       177490392  total_size($data_ref): 183760484
+8
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 6603 xxxxxxx   25   0 7208m 6.9g 1592 R 100.0 58.6   0:51.38 perl

T3: size($data_ref):       177490392  total_size($data_ref): 175598464
+9
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 6625 xxxxxxx   25   0 6315m 6.0g 1592 R 100.0 51.2   0:47.73 perl
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