日期字元串未在 while true 內更新；做循環

我有一個簡單的 bash 腳本：

#!/bin/bash

enp="$(ip route | grep "192.168.1.1" | cut -d' ' -f 3)"

while true; do
   vnstat -l -i "$enp" --style 4 --json | awk '{ print strftime("[%d/%b/%Y:%H:%M:%S]"), $0 }' >> raw/caching_server_network.json
   printf -- '-%.0s' {1..100}; echo "" >> raw/caching_server_network.json
   sleep 10
done

目前，此腳本會在每個 vnstat 輸出的開頭附加一個 strftime，並且每次呼叫都會更新 strftime。輸出：

[04/Jan/2022:13:31:17] {"index":1012,"seconds":2024,"rx":{"ratestring":"13.59 Mbit/s","bytespersecond":1698943,"packetspersecond":15220,"bytes":3397887,"packets":30441,"totalbytes":29895276777,"totalpackets":43496469},"tx":{"ratestring":"2.81 Gbit/s","bytespersecond":350918926,"packetspersecond":233842,"bytes":701837853,"packets":467685,"totalbytes":518923724379,"totalpackets":354639132}}
[04/Jan/2022:13:31:41] {"index":1013,"seconds":2026,"rx":{"ratestring":"206.68 Mbit/s","bytespersecond":25834765,"packetspersecond":31840,"bytes":51669531,"packets":63681,"totalbytes":29946946308,"totalpackets":43560150},"tx":{"ratestring":"3.15 Gbit/s","bytespersecond":394123782,"packetspersecond":269030,"bytes":788247565,"packets":538060,"totalbytes":519711971944,"totalpackets":355177192}}

我想做的是讓 datetime 字元串包含毫秒。但我面臨的問題是日期輸出不再更新。每次呼叫只是將相同的時間添加到字元串中。

我嘗試了以下方法：

#!/bin/bash

enp="$(ip route | grep "192.168.1.1" | cut -d' ' -f 3)"

while true; do
   vnstat -l -i "$enp" --style 4 --json | awk '{ print "'"$(date +%F:%T.%3N)"'", $0 }' >> raw/caching_server_network.json
   printf -- '-%.0s' {1..100}; echo "" >> raw/caching_server_network.json
   sleep 10
done

輸出：

04/Jan/2022:13:30:11.743 {"index":975,"seconds":1950,"rx":{"ratestring":"73.04 Mbit/s","bytespersecond":9130121,"packetspersecond":25590,"bytes":18260242,"packets":51181,"totalbytes":29368713172,"totalpackets":42315654},"tx":{"ratestring":"3.90 Gbit/s","bytespersecond":486961964,"packetspersecond":326200,"bytes":973923928,"packets":652400,"totalbytes":498158299423,"totalpackets":340676257}}
04/Jan/2022:13:30:11.743 {"index":976,"seconds":1952,"rx":{"ratestring":"12.23 Mbit/s","bytespersecond":1529119,"packetspersecond":17962,"bytes":3058239,"packets":35924,"totalbytes":29371771411,"totalpackets":42351578},"tx":{"ratestring":"4.18 Gbit/s","bytespersecond":522336815,"packetspersecond":346742,"bytes":1044673631,"packets":693484,"totalbytes":499202973054,"totalpackets":341369741}}

請注意，上述輸出中的日期時間對於兩行來說是相同的。在使用日期呼叫時，如何獲取每個 vnstat 呼叫更新的日期？

每次呼叫的時間都會改變vnstat，但如果vnstat輸出多行，它們都會收到相同的時間。這是因為 shell 執行date並將其輸出插入到 的參數中awk。

要為每一行獲取新的時間戳，您需要呼叫datefrom within awk。由於我vnstat的機器上沒有，我創建了一個更簡單的範例：

#! /bin/bash

while true; do
   for i in {1..3} ; do
       echo $i
       sleep .1
   done  | awk '{ system("date +%F:%T.%3N\\  | tr -d \\\\n"); print $0 }'
   printf -- '-%.0s' {1..80}; echo ""
   sleep 1
done

刪除時間戳後的tr換行符。

引用自：https://unix.stackexchange.com/questions/685187