$ zgrep -c 'Duplicate entry' exception.log-20150[567]*
exception.log-20150501.gz:5
exception.log-20150502.gz:3
exception.log-20150503.gz:11
exception.log-20150504.gz:7
exception.log-20150506.gz:6
exception.log-20150507.gz:6
exception.log-20150508.gz:2
exception.log-20150509.gz:1
exception.log-20150510.gz:5
exception.log-20150511.gz:5
exception.log-20150512.gz:0
exception.log-20150513.gz:4
exception.log-20150514.gz:2
exception.log-20150515.gz:4
exception.log-20150516.gz:3
exception.log-20150517.gz:5
exception.log-20150518.gz:2
exception.log-20150519.gz:8
exception.log-20150520.gz:0
exception.log-20150521.gz:3
exception.log-20150522.gz:1
exception.log-20150523.gz:1
exception.log-20150524.gz:4
exception.log-20150525.gz:1
exception.log-20150526.gz:1
exception.log-20150527.gz:2
exception.log-20150528.gz:36
exception.log-20150529.gz:3
exception.log-20150530.gz:5
exception.log-20150531.gz:1
exception.log-20150601.gz:1
exception.log-20150602.gz:1
exception.log-20150603.gz:4
exception.log-20150604.gz:2
exception.log-20150605.gz:3
exception.log-20150606.gz:1
exception.log-20150607.gz:3
exception.log-20150608.gz:1
exception.log-20150609.gz:5
exception.log-20150610.gz:193
exception.log-20150611.gz:212
exception.log-20150612.gz:524
exception.log-20150613.gz:37
exception.log-20150614.gz:363
exception.log-20150615.gz:859
exception.log-20150616.gz:463
exception.log-20150617.gz:347
exception.log-20150618.gz:355
exception.log-20150619.gz:806
exception.log-20150620.gz:558
exception.log-20150621.gz:359
exception.log-20150622.gz:230
exception.log-20150623.gz:125
exception.log-20150624.gz:54
exception.log-20150625.gz:49
exception.log-20150626.gz:55
exception.log-20150627.gz:54
exception.log-20150628.gz:22
exception.log-20150629.gz:11
exception.log-20150630.gz:19
exception.log-20150701.gz:27
exception.log-20150702.gz:45
exception.log-20150703.gz:13
exception.log-20150704.gz:17
exception.log-20150705.gz:9
exception.log-20150706.gz:9
exception.log-20150707.gz:54
exception.log-20150708.gz:43
exception.log-20150709.gz:15
exception.log-20150710.gz:21
exception.log-20150711.gz:26
exception.log-20150712.gz:74
exception.log-20150713.gz:22
exception.log-20150714.gz:50
exception.log-20150715.gz:52
exception.log-20150716.gz:47
exception.log-20150717.gz:42
exception.log-20150718.gz:40
exception.log-20150719.gz:40
exception.log-20150720.gz:19
exception.log-20150721.gz:56
exception.log-20150722.gz:111
exception.log-20150723.gz:107
exception.log-20150724.gz:55