https://stackoverflow.com/q/50728135

benchmark.txt

# WARNING # WARNING # WARNING # the following command generates a ~1 GIGABYTE file!

$ perl -le '$,=$/;for(1..50000){print+("Foo")x5000,"Bar CAPTURE Bar"}print+("Foo")x5000' >test.txt

# For testing outputs:
# perl -le '$,=$/;print"Bar CAPTURE Bar";for(1..49999){print+("Foo")x5000,"Bar CAPTURE Bar"}' >out_expect.txt

# UPDATE: Replace "time" with "/usr/bin/time" to get memory usage stats as well!

# https://stackoverflow.com/a/50728937
$ time perl -ne '$x&&push@b,$_;if(/CAPTURE/){$x||=@b=$_;print@b;@b=()}' test.txt >/dev/null
real	0m50.761s
user	0m50.560s
sys	0m0.196s

# https://stackoverflow.com/a/50728937
$ time perl -0777ne '/((^.*CAPTURE.*$)(?s:.*)(?2)(?:\z|\n))/m and print $1' test.txt >/dev/null
real	0m0.579s
user	0m0.328s
sys	0m0.248s

# https://stackoverflow.com/a/50728589
$ cat glenn.sh 
#!/bin/sh
sed -n '/CAPTURE/,$p' test.txt | tac | sed -n '/CAPTURE/,$p' | tac
$ time ./glenn.sh >/dev/null
real	0m48.955s
user	0m48.900s
sys	0m2.852s

# https://stackoverflow.com/a/50728348
$ time awk '/CAPTURE/ && NR==FNR {a[++f]=NR; next} a[1]<=FNR && FNR<=a[f]' test.txt{,} >/dev/null
real	1m36.760s
user	1m36.476s
sys	0m0.276s

# https://stackoverflow.com/a/50729789
$ cat walter1.sh 
#!/bin/sh
echo "/CAPTURE/,?CAPTURE? p" | ed -s test.txt
$ time ./walter1.sh >/dev/null
real	0m29.214s
user	0m25.156s
sys	0m2.628s

# https://stackoverflow.com/a/50729789
$ time sed -n '1,/CAPTURE/{h;n};H;/CAPTURE/{x;p;n;h};' test.txt >/dev/null
real	0m29.852s
user	0m29.676s
sys	0m0.172s