Add timestamp to cat output from shell script

问题:

I have a small script that cats the output from the ttyUSB to a file I would like to prepend a timestamp to each line. From the command line this does everything I want:

$ cat /dev/ttyUSB0 /home/pi/daily_logs/ttyUSSB0 | awk '{ print strftime("%Y-%m-%d %H:%M:%S"), $0; }

My issue is that when I add it to a script everything works but the awk timestamp isn't added. My script line looks like this:

cat < /dev/ttyUSB0 > /home/pi/daily_logs/ttyUSB0 | awk '{ print strftime("%Y-%m-%d %H:%M:%S"), $0; } &

Any help getting this going would be appreciated.

回答1:

You need to redirect awk's output to the file, not cat's. The way you have it, awk gets nothing. Actually, you may not need cat at all:

awk '{ print strftime("%Y-%m-%d %H:%M:%S"), $0; }' /dev/ttyUSB0 > /home/pi/daily_logs/ttyUSB0 &

回答2:

You need to put the > /home/pi/daily_logs/ttyUSB0 after the pipe. Like so:

cat < /dev/ttyUSB0 | awk '{ print strftime("%Y-%m-%d %H:%M:%S"), $0; }' > /home/pi/daily_logs/ttyUSB0

回答3:

Useless use of cat is impeding the solution. To minimize the changes needed, you can also do:

< /dev/ttyUSB0 > /home/pi/daily_logs/ttyUSB0 awk '...' &