bash计时器的实现案例：检查并记录网络稳定性的脚本

e13e

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。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82

#!/bin/bash #set -o errexit export SCRIPT=$0 SID=$PPID usage(){     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\tPrint this info"     echo -e "Example:"     echo -e "\tbash $0 -W 1 -I 3 -i 127.0.0.1 -L error -log /tmp/${SCRIPT}-${SID}.log"     echo -e "\tbash $0"     exit 255 } [ $# -eq 4 ] && usage # 默认参数 LOGFILE="/tmp/${SCRIPT}-${SID}.log" touch $LOGFILE TIMEOUT=1 INTERVAL=10 LEVEL=info IP=127.0.0.1 MyIP=$(ip addr sh eth0 |awk '/^[\ ]*inet /{split($2,IP,"/");printf IP[1]}') # 参数获取 TEMP=$(getopt -o W:I:i:L:l:h --long timeout:,interval:,ip:,level:,log:,help -- "$@") [ $? != 0 ] && usage eval set -- "$TEMP" # 参数处理 while true; do     case "$1" in         -W|--timeout) TIMEOUT=$2; shift 2;;         -I|--interval) INTERVAL=$2; shift 2;;         -i|--ip) IP=$2; shift 2;;         -L|--level) LEVEL=$2; shift 2;;         -l|--log) LOGFILE=$2; shift 2;;         -h|--help) usage; shift;;         --) shift; break ;;     esac done [ "$IP" = "" ] && usage adjust(){     return $((SECONDS%INTERVAL)) } pinger(){     ping $1 -W $TIMEOUT -c 1 | 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\" >> $LOGFILE && exit 0"  1 2 9 15 } trapper logger "START($SID)\t$MyIP -> $IP" >> $LOGFILE while true do     if adjust; then         unset t         t=$(pinger $IP)         if [ "$t" = "" ]; then             logger "ERROR($SID)\t$MyIP -> $IP ${TIMEOUT}(S)" >> $LOGFILE &         else             [ "$LEVEL" = "erorr" ] || logger "INFO($SID)\t$MyIP -> $IP ${t}(ms)" >> $LOGFILE &         fi         sleep 1     fi     sleep 0.1 done

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 17:24:50 START(26729)192.168.202.2 -> a.b.c
2015-04-28 17:24:50 INFO(26729)192.168.202.2 -> a.b.c 0.630(ms)
2015-04-28 17:24:52 INFO(26729)192.168.202.2 -> a.b.c 0.575(ms)
2015-04-28 17:24:54 INFO(26729)192.168.202.2 -> a.b.c 0.875(ms)