個人常用的 awk 命令

1. 格式化某些 /proc 文件輸出

Linux下有些 proc 文件的輸出內容確實沒法看，比如/proc/net/snmp的輸出如下：

[root@localhost ~]# cat /proc/net/snmp 
Ip: Forwarding DefaultTTL InReceives InHdrErrors InAddrErrors ForwDatagrams InUnknownProtos InDiscards InDelivers OutRequests OutDiscards OutNoRoutes ReasmTimeout ReasmReqds ReasmOKs ReasmFails FragOKs FragFails FragCreates
Ip: 2 64 1112736 0 0 0 0 0 1112733 1112545 0 36 0 0 0 0 0 0 0
Icmp: InMsgs InErrors InCsumErrors InDestUnreachs InTimeExcds InParmProbs InSrcQuenchs InRedirects InEchos InEchoReps InTimestamps InTimestampReps InAddrMasks InAddrMaskReps OutMsgs OutErrors OutDestUnreachs OutTimeExcds OutParmProbs OutSrcQuenchs OutRedirects OutEchos OutEchoReps OutTimestamps OutTimestampReps OutAddrMasks OutAddrMaskReps
Icmp: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Tcp: RtoAlgorithm RtoMin RtoMax MaxConn ActiveOpens PassiveOpens AttemptFails EstabResets CurrEstab InSegs OutSegs RetransSegs InErrs OutRsts InCsumErrors
Tcp: 1 200 120000 -1 2207 2204 4 598 3803 1112646 1112462 0 0 303 0
Udp: InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors IgnoredMulti
Udp: 176 0 0 91 0 0 0 0
UdpLite: InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors InCsumErrors IgnoredMulti
UdpLite: 0 0 0 0 0 0 0 0

第一行是字段，第二行是字段的值。這些輸出每一行包含的字段太多，字段和值又沒對齊，看着太費勁，遂用awk命令格式化下這類輸出，以後方便查看。
awk命令如下：

awk '{\
    if (NR % 2 == 0) print $1;\
    for(i = 2; i <= NF; i++) {\
        if (NR % 2 ) \
            count[i] = $i;\
        else if ($i > 0) \
            printf("    %-28s:%d\n",count[i], $i);\
    }\
}' \
/proc/net/snmp

格式化後的效果如下：

Ip:
    Forwarding                  2
    DefaultTTL                  64
    InReceives                  2252593
    InDelivers                  2252590
    OutRequests                 2252398
    OutNoRoutes                 36
Icmp:
Tcp:
    RtoAlgorithm                1
    RtoMin                      200
    RtoMax                      120000
    ActiveOpens                 3807
    PassiveOpens                3804
    AttemptFails                4
    EstabResets                 598
    CurrEstab                   7003
    InSegs                      2252503
    OutSegs                     2252315
    OutRsts                     303
Udp:
    InDatagrams                 176
    OutDatagrams                91
UdpLite:

上述命令按格式打印非0值的字段和值。該命令也適合/proc/net/netstat文件。
結合watch命令就能定時得查看這些值的變化，命令如下：

watch -n 1 "awk '{if (NR % 2 == 0) print \$1;for(i = 2; i <= NF; i++) {if (NR % 2 ) count[i]=\$i; else if (\$i > 0 ) printf(\"    %-28s%d\n\",count[i], \$i);}}' /proc/net/netstat"

更進一步，watch 命令只能看到某個時間點的數值統計，如果想查看每秒鐘數值的變化，就不那麼容易了，我花了些時間寫了如下命令來實現這個效果：

echo '' > tmp.txt; \
for((i = 1; ; i++)); do \
    awk '{for(i = 2; i <= NF; i++) {if (NR % 2 ) count[i] = $i; else if ($i > 0 ) print count[i], $i;}}' \
        /proc/net/snmp /proc/net/netstat >> tmp.txt; \
    if [ `expr $i % 2` == 0 ]; then \
        printf "\033c"; \
        awk '{if (a[$1]) {if ($2 != a[$1]) printf("%-28s%d\n", $1, $2 - a[$1])} else a[$1] = $2;}' tmp.txt; \
        echo '' > tmp.txt;\
    else \
        sleep 1;\
    fi; \
done

這個命令會每秒鐘輸出/proc/net/snmp 和 /proc/net/netstat文件中數值的變化，輸出格式如下：

InReceives                  76931
InDelivers                  76931
OutRequests                 76931
InMsgs                      4
InEchos                     2
InEchoReps                  2
OutMsgs                     4
OutEchos                    2
OutEchoReps                 2
InType0                     2
InType8                     2
OutType0                    2
OutType8                    2
ActiveOpens                 200
PassiveOpens                166
EstabResets                 200
CurrEstab                   132
InSegs                      76927
OutSegs                     76927
OutRsts                     100
DelayedACKs                 1114
DelayedACKLocked            2
ListenOverflows             34
ListenDrops                 34
TCPHPHits                   15774
TCPPureAcks                 339
TCPHPAcks                   35402
TCPAbortOnClose             100
TCPOrigDataSent             41348
InOctets                    46293624
OutOctets                   46300484
InNoECTPkts                 77482