Another alternative and performance/memory comparison

dedupe

@@ -10,8 +10,20 @@ function usage_exit {
 if [[ "$1" == '-h' || "$1" == '--help' ]]; then usage_exit 0; fi
 if [[ $# -ne 2 ]]; then usage_exit 1; fi
 
-# Perl seems to be ~30 % faster than AWK for this, but grep is ~2-3 times faster than Perl.
-# AWK uses the least memory, Perl about 1.5 times as much, grep twice as much (as AWK).
+# Performance and memory comparison using <(seq 1000000 2048575) <(seq 1000000 2048575)  (i.e. 8 MiB of input data, all lines in both files), median of 9 runs:
+#
+# Implementation | User time | Sys time | Peak RSS
+#                |       [s] |      [s] |    [MiB]
+# ---------------|-----------|----------|---------
+# AWK            |      1.16 |     0.03 |     86.8
+# Perl           |      0.90 |     0.06 |    149.6
+# Python         |      0.58 |     0.06 |    112.6
+# grep           |      0.36 |     0.07 |    216.9
+#
+# Exact command executed for these tests, with warmup:
+#  { for i in {0..3}; do ./dedupe <(seq 1000000 2048575) <(seq 1000000 2048575) >/dev/null; done; for i in {0..8}; do /usr/bin/time -v ./dedupe <(seq 1000000 2048575) <(seq 1000000 2048575) 2> >(grep -F -e ' time ' -e 'Maximum resident' >&2) | cat >/dev/null; done; } |& sort
+
 #awk 'NR==FNR { s[$0]=1; next; }  !($0 in s)' "$1" "$2"
 #perl -ne 'if (@ARGV == 1) { $seen{$_}=1; } else { print $_ if !(exists $seen{$_}); }' "$1" "$2"
+#python3 -c 'import sys'$'\n''s={}'$'\n''with open(sys.argv[1], "r") as fp:'$'\n'' for line in fp:'$'\n''  s[line]=True'$'\n''with open(sys.argv[2], "r") as fp:'$'\n'' for line in fp:'$'\n''  if line not in s:'$'\n''   print(line, end="")' "$1" "$2"
 grep -F -x -v -f "$1" "$2"