尾巴-f不显示最后几行

Question

I'm doing a scrip that reads from a log and send the line throught netcat

tail -f /tmp/archivo.txt | grep --line-buffered status=bounced | while read LINE0 
do 
    echo "${LINE0}"
    echo "${LINE0}" > /tmp/mail-line.log
    netcat localhost 5699 < /tmp/mail-line.log 
    sleep 1s
done

When I first launch this script it properly sends the data but when a new line is introduced it doesn't work unless I relaunch the script, any ideas? Thank you.

Edit:

As @Kamil Cuk asked me, I tried only doing echos, it didn't work

What's happening?:

Well, I was introducing the new data using gedit, but this didn't work whit the -f flag but instead with the -F flag because it says that archivo.txt has been replaced. I tried doing echo "New line with bounce=status" >> archivo.txt" and it worked. So I'm assuming that gedit somehow changes metadata and tail doesn't show anything with -f thats why it's not working.

Answer 1

Under the hood files in the filesystem are just identified by numbers, called " inodes ". Then you have a text label that points to the inode, called a "file name". When you run tail -f filename you start tailing the file behind the inode that filename currently points to; this is called "opening a file handle " because the tail program creates an open reference to the file through a "file handle".

What happened in your case is that you started tailing one file. Then your logging application (gedit :-) ) created a new file on a different inode and changed what inode filename refers to. The file at the inode that you are tailing still exists because tail still have an open file handle, it won't get removed until all programs close their file handles. But any new program that tries to open the file will get to the new inode.

To get around this you need to open the file in "append mode" (there are other modes as well). "Append mode" means you are pushing data to the end of the file without creating a new inode. All real logging applications will do this since it is much faster than rewriting the entire file every time.