bash的帮助中提到SECONDS系统变量：
SECONDS Each time this parameter is referenced, the number of seconds since shell invocation is returned. If a value is assigned to SECONDS, the value returned upon subsequent references is the number of seconds since the assignment plus the value assigned. If SECONDS is unset, it loses its special properties, even if it is subsequently reset.
我们在程序执行期间，检查这个变量，即可实现记时的功能。
本例是用来每隔一个固定时间，ping一个IP，出现故障时记录下来的脚本。
#!/bin/bash#set-oerrexitexportSCRIPT=$0SID=$PPIDusage(){echo-e”Usage:”echo-e”\tbash$0[OPTs]”echo-e”\t-W|–timeout\t\t<M>”echo-e”\t-I|–interval\t\t<N>”echo-e”\t-i|–ip\t\t\t<A.B.C.D>”echo-e”\t-L|–level\t\t<info|error>”echo-e”\t-l|–log\t\t</tmp/${SCRIPT}-${SID}.log>”echo-e”\t-h\t\t\tPrintthisinfo”echo-e”Example:”echo-e”\tbash$0-W1-I3-i127.0.0.1-Lerror-log/tmp/${SCRIPT}-${SID}.log”echo-e”\tbash$0″exit255}[$#-eq4]&&usage#默认参数LOGFILE=”/tmp/${SCRIPT}-${SID}.log”touch$LOGFILETIMEOUT=1INTERVAL=10LEVEL=infoIP=127.0.0.1MyIP=$(ipaddrsheth0|awk’/^[\]*inet/{split($2,IP,”http://wangxiaoyu.blog.51cto.com/”);printfIP[1]}’)#参数获取TEMP=$(getopt-oW:I:i:L:l:h–longtimeout:,interval:,ip:,level:,log:,help–“$@”)[$?!=0]&&usageevalset–“$TEMP”#参数处理whiletrue;docase”$1″in-W|–timeout)TIMEOUT=$2;shift2;;-I|–interval)INTERVAL=$2;shift2;;-i|–ip)IP=$2;shift2;;-L|–level)LEVEL=$2;shift2;;-l|–log)LOGFILE=$2;shift2;;-h|–help)usage;shift;;–)shift;break;;esacdone[“$IP”=””]&&usageadjust(){return$((SECONDS%INTERVAL))}pinger(){ping$1-W$TIMEOUT-c1|tail-1|awk-F/'{print$(NF-1)}’2>/dev/null}logger(){echo-e”$(date+%F””%T)\t””$@”}trapper(){trap”logger\”EXIT($SID)\t$MyIP->$IP\”>>$LOGFILE&&exit0″12915}trapperlogger”START($SID)\t$MyIP->$IP”>>$LOGFILEwhiletruedoifadjust;thenunsettt=$(pinger$IP)if[“$t”=””];thenlogger”ERROR($SID)\t$MyIP->$IP${TIMEOUT}(S)”>>$LOGFILE&else[“$LEVEL”=”erorr”]||logger”INFO($SID)\t$MyIP->$IP${t}(ms)”>>$LOGFILE&fisleep1fisleep0.1done
执行
bash pinger.sh -W 1 -I 2 -i a.b.c &
执行结果如下：
# tail -f -n 10 /tmp/bash-26729.log
2015-04-28 17:24:50START(26729)192.168.202.2 -> a.b.c
2015-04-28 17:24:50INFO(26729)192.168.202.2 -> a.b.c 0.630(ms)
2015-04-28 17:24:52INFO(26729)192.168.202.2 -> a.b.c 0.575(ms)
2015-04-28 17:24:54INFO(26729)192.168.202.2 -> a.b.c 0.875(ms)
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