regex - performance grep vs perl -ne -

regex - performance grep vs perl -ne -

i made performance test surprising result: perl more 20 times faster!

is normal? result regular expression? egrep far slower grep? ... tested on current cygwin , current opensuse 13.1 in virtualbox.

fastest test perl:

time zcat log.gz \ | perl -ne 'print if ($_ =~ /^\s+\s+\s+\s+(error|warning|severe)\s/ )' | tail 2014-06-24 14:51:43,929 severe ajp-0.0.0.0-8009-13 sessiondataupdatemanager cannot register active info when window has no name 2014-06-24 14:52:01,031 error hfn si threadpool(4)-442 cepeventunmarshaler unmarshaled events duration: 111 2014-06-24 14:52:03,556 error hfn si threadpool(4)-444 cepeventunmarshaler unmarshaled events duration: 52 2014-06-24 14:52:06,789 severe ajp-0.0.0.0-8009-1 sessiondataupdatemanager cannot register active info when window has no name 2014-06-24 14:52:06,792 severe ajp-0.0.0.0-8009-1 sessiondataupdatemanager cannot register active info when window has no name 2014-06-24 14:52:07,371 severe ajp-0.0.0.0-8009-9 sessiondataupdatemanager cannot register active info when window has no name 2014-06-24 14:52:07,373 severe ajp-0.0.0.0-8009-9 sessiondataupdatemanager cannot register active info when window has no name 2014-06-24 14:52:07,780 severe ajp-0.0.0.0-8009-11 sessiondataupdatemanager cannot register active info when window has no name 2014-06-24 14:52:07,782 severe ajp-0.0.0.0-8009-11 sessiondataupdatemanager cannot register active info when window has no name 2014-06-24 15:06:24,119 error hfn si threadpool(4)-443 cepeventunmarshaler unmarshaled events duration: 117 real 0m0.151s user 0m0.062s sys 0m0.139s

fine!

far slower test egrep:

time zcat log.gz \ | egrep '^\s+\s+\s+\s+(error|warning|severe)\s' | tail ... real 0m2.454s user 0m2.448s sys 0m0.092s

(output same above...)

finally slower grep different notation (my first try)

time zcat log.gz \ | egrep '^[^\s]+\s+[^\s]+\s+(error|warning|severe)\s' | tail ... real 0m4.295s user 0m4.272s sys 0m0.138s

(output same above...)

the ungzipped file size 2.000.000 lines un-gzip-ped 500mbytes - matching line count small.

my tested versions:

opensuse grep (gnu grep) 2.14 cygwin grep (gnu grep) 2.16

perhaps bug newer grep versions?

you tricked operating system's cache. when reading , grepping files layers filesystem walked through:

harddrive own cache os read cache

to know what's going on it's thought warm these caches running tests work not count. after these test stop runnning time.

regex perl grep