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Questions tagged [tail]

Watching updates at the end of a file, with or without the tail utility

250
votes
19answers
172k views

How to have tail -f show colored output

I'd like to be able to tail the output of a server log file that has messages like: INFO SEVERE etc, and if it's SEVERE, show the line in red; if it's INFO, in green. What kind of alias can I setup ...
119
votes
6answers
231k views

cat line X to line Y on a huge file

Say I have a huge text file (>2GB) and I just want to cat the lines X to Y (e.g. 57890000 to 57890010). From what I understand I can do this by piping head into tail or viceversa, i.e. head -A /...
109
votes
4answers
10k views

Does tail read the whole file?

If I want to tail a 25 GB textfile, does the tail command read the whole file? Since a file might be scattered on a disk I imagine it has to, but I do not understand such internals well.
103
votes
5answers
273k views

How to monitor only the last n lines of a log file?

I have a growing log file for which I want to display only the last 15 lines. Here is what I know I can do: tail -n 15 -F mylogfile.txt As the log file is filled, tail appends the last lines to the ...
100
votes
1answer
30k views

How to do a `tail -f` of log rotated files?

On a long running system I usually have a terminal with $ tail -f /var/log/kern.log or something like this open. But from time to time I have to restart such command because no new messages are ...
56
votes
3answers
93k views

How does the “tail” command's “-f” parameter work?

$ tail -f testfile the command is supposed to show the latest entries in the specified file, in real-time right? But that's not happening. Please correct me, if what I intend it to do is wrong... I ...
53
votes
2answers
31k views

Observe multiple log files in one output

Is there an easy way to do something like tail -f mylogfile but to have the changes of more than one file displayed (maybe with the file name added as prefix to each line)? Or maybe a GUI tool? I am ...
52
votes
9answers
34k views

How to obtain inverse behavior for `tail` and `head`?

Is there a way to head/tail a document and get the reverse output; because you don't know how many lines there are in a document? I.e. I just want to get everything but the first 2 lines of foo.txt ...
52
votes
5answers
21k views

monitor files (à la tail -f) in an entire directory (even new ones)

I normally watch many logs in a directory doing tail -f directory/*. The problem is that a new log is created after that, it will not show in the screen (because * was expanded already). Is there a ...
50
votes
2answers
25k views

The 'less' command-line equivalent of 'tail -f'

I would like to open up a file using less, and have it automatically scroll the file similar to tail -f. I know that I can do less file, and then hit Shift-F to forward forever; like tail -f. I need ...
49
votes
6answers
63k views

Best way to follow a log and execute a command when some text appears in the log

I have a server log that outputs a specific line of text into its log file when the server is up. I want to execute a command once the server is up, and hence do something like the following: tail -f ...
45
votes
5answers
53k views

Output file contents while they change

I want to output a file's contents while they change, for example if I have the file foobar and I do: magic_command foobar The current terminal should display the file's contents and wait until, I ...
37
votes
2answers
22k views

What is the difference between “tail -f” and “tail -F”?

I never used tail -F command instead always used tail -f however someone told me that -F is better without much explanation. I looked up man page for tail command. -f output appended data as the ...
35
votes
4answers
59k views

Grep from the end of a file to the beginning

I have a file with about 30.000.000 lines (Radius Accounting) and I need to find the last match of a given pattern. The command: tac accounting.log | grep $pattern gives what I need, but it's too ...
35
votes
2answers
14k views

Does less have a feature like tail --follow=name (-F)

The command less can be used to replace tail in tail -f file to provide features like handling binary output and navigating the scrollback: less +F file The + prefix means "pretend I type that ...
35
votes
7answers
19k views

How do I make Vim behave like “tail -f”?

I would like to know if there is a way to make Vim behave like tail -f. Even the best Vim plugin I've found so far doesn't do what I expect. I really want to see the file update in real-time. Even I'...
34
votes
4answers
9k views

Why does “tail -f … | tail” fail to produce any output?

Why does the following command not produce any output? $ tail -f /etc/passwd | tail After reading about buffering, I tried the following to no avail: $ tail -f /etc/passwd | stdbuf -oL tail Note ...
34
votes
7answers
32k views

How to tail multiple files using tail -0f in Linux/AIX

I tried tailing two files using the option: tail -0f file1.log -0f file2.log In Linux I see an error "tail : can process only one file at a time". In AIX I see the error as "Invalid options". This ...
33
votes
3answers
28k views

Tail log file on multiple machines over ssh

I'm trying to tail a log file on multiple remote machines and forward the output to my local workstation. I want connections to close when pressing Ctrl-C. At the moment I have the following function ...
32
votes
1answer
14k views

Do I need to worry about “tail: unrecognized file system type 0xbeefdead”?

I'm trying to follow a regular text file with tail -f -n 50 filename. I get the information from the file just fine, except I always get this error message: tail: unrecognized file system type ...
31
votes
1answer
6k views

Is `tail -f` more efficient than `less +F`?

This article pointed out some reasons to use less +F over tail -f. Most of the reasons are about the features, not technical reasons: less +F can highlight, search, navigate through file. How about ...
29
votes
3answers
65k views

Piping from grep to awk not working

I am trying to grep the ongoing tail of file log and get the nth word from a line. Example file: $ cat > test.txt <<EOL Beam goes blah John goes hey Beam goes what? John goes forget it Beam ...
28
votes
4answers
9k views

How to do a continous 'wc -l' with gnu texttools?

I know of course that cat logfile.txt | wc -l 120 will tell me the number of lines in a file. Whereas tail -f logfile.txt will show me the new lines that another program writes to logfile.txt. ...
27
votes
8answers
32k views

grep and tail -f?

Is it possible to do a tail -f (or similar) on a file, and grep it at the same time? I wouldn't mind other commands just looking for that kind of behavior.
27
votes
3answers
16k views

How can I do the equivalent of tail -f with ls? [duplicate]

Possible Duplicate: Is it possible to follow a command (run repeatedly)? as one would follow a file using tail -f? I would like to monitor files that are being downloaded to a directory in real ...
27
votes
3answers
9k views

How do I “cat and follow” a file?

A file is being sequentially downloaded by wget. If I start unpacking it with cat myfile.tar.bz2 | tar -xj, it may unpack correctly or fail with "Unexpected EOF", depending on what is faster. How to ...
24
votes
2answers
2k views

'tail -f' for a specific amount of time [duplicate]

I need to run tail -f against a log file, but only for specific amount of time, for example 20 seconds, and then exit. What would be an elegant way to achieve this?
23
votes
9answers
52k views

Command to display first few and last few lines of a file

I have a file with many rows, and each row has a timestamp at the starting, like [Thread-3] (21/09/12 06:17:38:672) logged message from code..... So, I frequently check 2 things from this log file. ...
23
votes
6answers
5k views

Is there a way to make tail -F beep?

Is there a way to make tail -F or less beep (ring the bell in a terminal) when new data comes in (a new line is added to the file). Or is there any other unix utility to do this on a linux or mac.
21
votes
3answers
14k views

Follow a pipe using less?

Can less follow (by pressing F) a piped input (similarly to a file)? For a file that is being written to, the command less <file> will follow the file when pressing F. But if I have a command ...
20
votes
4answers
15k views

How to quit `tail -f` mode without using `Ctrl+c`?

When I do tail -f filename, how to quit the mode without use Ctrl+c to kill the process? What I want is a normal way to quit, like q in top. I am just curious about the question, because I feel ...
20
votes
6answers
9k views

How keep last 50 lines in logfile

I try to keep last 50 lines in my file where I save temperature every minute. I used this command: tail -n 50 /home/pi/Documents/test > /home/pi/Documents/test But the result is empty test file. ...
19
votes
4answers
6k views

How can I see the whole file and also wait for more data to be added to that file?

I want to read whole file and make it waiting for input, just like tail -f but with the complete file displayed. The length of this file will always change, because this is a .log file. How can I ...
19
votes
7answers
19k views

`tail -f` until text is seen

I've got a CI server with a command-line interface that allows me to remotely kick-off a job (jenkins CI server and the jenkins-cli.jar tool). After I kick the job off I tail -f the log (sorry for ...
19
votes
2answers
3k views

Coloring different sources for tail

I'm watching different logs by tail -q -f /var/log/syslog -f /var/log/fail2ban.log -f /var/log/nginx/error.log How can I have the output of each log colored differently?
18
votes
3answers
14k views

Open a text file and let it update itself

How can I open a text file and let it update itself? Similar to the way top works. I want to open a log file and watch it update itself on the fly. I have just tried: $ tail error.log But just ...
17
votes
4answers
139k views

How to get lines 10 to 100 from a 200 line file into a new file [duplicate]

I have file with 200 lines. I need to extract lines from 10 to 100 and put them into a new file. How do you do this in unix/Linux? What are the possible commands you could use?
17
votes
2answers
1k views

Editing text file with Vim does not update tail -f

I'm using tail -f a.txt to watch updates on a file called a.txt. If I update the file using something like ls -a >> a.txt in a second virtual console, the changes will display in real-time in ...
17
votes
1answer
11k views

Convert newlines to null-delimited when using tail

How can I change the output from tail to use null-terminated lines instead of newlines? My question is similar to this one: How to do `head` and `tail` on null-delimited input in bash?, but differs ...
17
votes
1answer
3k views

How to do `head` and `tail` on null-delimited input in bash?

find command can output names of files as a null-delimited strings (if -print0 is provided), and xargs can consume them with -0 option turned on. But in between, it's hard to manipulate that ...
16
votes
1answer
765 views

How to get an average pipe flow speed

If myfile is increasing over time, I can get the number of line per second using tail -f | pv -lr > /dev/null It gives instantaneous speed, not average. How can I get the average speed (i.e the ...
15
votes
3answers
25k views

View only the new entries in a growing log file

tail -f x.log I use this command to see a growing log file in the command prompt. I am interested only in seeing the log lines that are written to the file after running tail -f and not interested ...
15
votes
3answers
41k views

continuous reading from named pipe (cat or tail -f)

I have configured rsyslog to log certain log events to /dev/xconsole: *.*;cron.!=info;mail.!=info |/dev/xconsole /dev/xconsole is a named pipe (fifo). If I want to see what is being logged, I ...
14
votes
6answers
23k views

How do you keep only the last n lines of a log file?

A script I wrote does something and, at the end, appends some lines to its own logfile. I'd like to keep only the last n lines (say, 1000 lines) of the logfile. This can be done at the end of the ...
14
votes
1answer
1k views

Why does piping to 'tail' change the contents of a line?

When I view the result of a SELECT with MySQL Workbench, it's correct with one single \ max@host 10:13:58: ~$ mysql -h db-master.domain.local -uuser -ppw db -e ' > SELECT > ...
14
votes
2answers
28k views

How to use tail -f with grep to show surrounding lines

I would like to see the output in a logfile greped by only one domain but also the following two lines. Example: tail -f /var/log/apache2/modsec_audit.log |grep mydomain.de this shows all lines, ...
14
votes
4answers
30k views

Combining tail && journalctl

I'm tailing logs of my own app and postgres. tail -f /tmp/myapp.log /var/log/postgresql/postgresql.main.log I need to include pgpool's logs. It used to be syslog but now it is in journalctl. Is ...
14
votes
2answers
3k views

“tail -f | iconv -fsjis” does not output anything

I want to tail -f a file, but its content is in sjis encoding, so I need to have it converted to the native (utf-8) encoding of my terminal. When I do tail -f x | iconv -fsjis there will be no ...
13
votes
3answers
1k views

tail -f, insert line break after log is idle for 3 seconds?

When doing a tail -f error.log, how to insert programmatically a line break after nothing has been appened to the file for 3 seconds ? (obviously, once one line break has been added, no other line ...
12
votes
2answers
1k views

How to start tailing a file that has not been yet created

I use tail to monitor the progress of jobs that I know will write their progress to disk. Almost always, I know which file they will create before they start running (the jobs are dispatched by a ...