tail -f，awk并输出到文件>

Question

I am attempting to filter a log file and am running into issues, what I have so far is the following, which does not work,

tail -f /var/log/squid/accesscustom.log | awk '/username/;/user-name/ {print $1; fflush("")}' | awk '!x[$0]++' > /var/log/squid/accesscustom-filtered.log

The goal is to take a file that contains

ipaddress1 username
ipaddress7
ipaddress2 user-name
ipaddress1 username
ipaddress5
ipaddress3 username
ipaddress4 user-name

and save to accesscustom-filtered.log

ipaddress1
ipaddress2
ipaddress3
ipaddress4

It works without the output to accesscustom-filtered.log but something in the > isn't working right and the file ends up empty.

Edit: Changed the original example to be correct

Answer 1

Use tee :

tail -f /var/log/squid/accesscustom.log | awk '/username/;/user-name/ {print $1}' | tee /var/log/squid/accesscustom-filtered.log

See also: Writing “tail -f” output to another file and Turn off buffering in pipe

Note: awk doesn't buffer like grep in the superuser example, so you shouldn't need to do anything special with your awk command. ( more info )