Stop using tail -f (mostly)
I still see a lot of people using
tail -f to monitor files that are changing, mostly log files. If you are one of them, let me show you a better alternative:
less documentation explains well what this
+F is all about:
Scroll forward, and keep trying to read when the end of file is reached. Normally this command would be used when already at the end of the file. It is a way to monitor the tail of a file which is growing while it is being viewed. (The behavior is similar to the “tail -f” command.)
So it says that it’s similar to
tail -f, but why I think it’s better?
Simply put, it allows you to switch between navigation and watching mode. We all have been there: You are watching a file with
tail -f, and then you need to search for something in this file, or just navigate up and down.
Now you need to exit
tail (or open a new shell), and
ack this file or open it with
vim to find what you are looking for. After that, you run
tail again to continue watching the file. There’s no need to do that when
you are using
Let’s say you want to watch the file
$ less +F production.log Important log information here Waiting for data... (interrupt to abort)
Here you have pretty much the same behaviour you’d get with
Now let’s say something interesting appears, and you want to search all the occurrences of “foo”. You can just hit
Ctrl-c to go to “normal”
mode (as if you had opened the file without the
+F flag), and then you have all the normal
less features you’d expect, including the search with
/foo. You can go to the next or previous occurrence with
up and down with
k, create marks with
m and do all sort of things that
less(1) says you can do.
Once you are done, just hit
F to go back to watching mode again. It’s that easy.
When not to use less
When you need to watch multiple files at the same time,
tail -f can actually give you a better output. It will show you something like this:
$ tail -f *.txt ==> file1.txt <== content for first file ==> file2.txt <== content for second file ==> file3.txt <== content for third file
When a change happens, it prints the file name and the new content, which is quite handy.
less, it would be like this:
$ less +F *.txt content for first file
It shows the content of just one file at a time. If you want to see what’s happening in the second file, you need to first
Ctrl-c to go to normal mode, then type
:n to go to the next buffer, and then
F again to go back to the watching mode.
Depending on your needs, it might still be worth to use
less for multiple files, but most of the time I just go with
tail for these cases. The important thing is to know the tools that we have available and use the right one
for the job at hand.
Статья на сайте softdroid.net: Блог о файлах и данных: Перестаньте использовать -f (часто)
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