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Questions tagged [tail]

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

118
votes
6answers
230k 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 /...
250
votes
19answers
171k 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 ...
99
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 ...
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. ...
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 ...
7
votes
5answers
2k views

Display only the penultimate (second last) row of a text [duplicate]

I have a poem with an unknown number of rows and I want to display only the penultimate one. What command should I use?
4
votes
1answer
660 views

make tail -f exit on a broken pipe

I want to watch a file until a bit of text appears I found this answer: `tail -f` until text is seen but when I tried it on ubuntu, it doesn't exit: $ echo one > test.txt $ echo two >> ...
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 ...
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 ...
29
votes
3answers
64k 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 ...
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 ...
0
votes
1answer
864 views

How to Tail -f output with colors using only Awk and show the rest of the output?

I was able to do a tail -f output with colors using the awk command. But I'm unsure how to output the rest of the log as it seems to be filtering only those 2 lines. I also want to see the other lines ...
108
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.
49
votes
6answers
62k 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 ...
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 ...
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.
9
votes
2answers
2k views

Is it possible to follow a command (run repeatedly)? as one would follow a file using tail -f?

I have a script which produces a file 'Detail.out'. I know that the script is completed whenever the file contains a certain number of lines (roughly 21025). So I find myself sitting at the command ...
7
votes
3answers
46k views

How do I tail a log file and keep tailing it when the latest one changes date?

I'm using RHEL 4. The normal tail -F file_name*.log doesn't update when the time flips over to 0000. Here's what I've tried so far from searching the web, both of which try to use nested tail: ...
5
votes
2answers
5k views

Tail -f piped through grep not outputing to file, but outputs to console

I'm using the following command tail -f /mydir/myfile | grep "searchterm" >> outfile Without the -f it works fine, but with the -f, which I need, nothing is written to the file. The following ...
103
votes
5answers
272k 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 ...
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 ...
51
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 ...
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 ...
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 ...
27
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. ...
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 ...
5
votes
4answers
13k views

Tail -f the most recent log file

In a few spots I got this to work ls -rt /path/to/log/file/ | tail -1 | xargs tail -f But I can't figure out why it won't always work (This is quick fix until I get the log rolling fixed here)
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 ...
15
votes
3answers
24k 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 ...
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 ...
8
votes
1answer
2k views

tail -f but suck in content of the file first (aka `cat -f`)

I need to display whole file before tracking it for a new changes, not only the last 10 lines (yep, I know it's not tail conceptually). In other words, something like cat -f would do, if it would ever ...
10
votes
4answers
1k views

What is the easiest way to execute text from tail at the command line?

Sometimes I'm working on a new (ubuntu) box and I type git and am alerted: The program 'git' is currently not installed. You can install it by typing: apt-get install git-core If that happens I ...
3
votes
2answers
359 views

How can I monitor a file that fully recreates during its run?

This is a follow-up question of Why are some file changes not shown in tail -f? With the use of capital F: tail -F I can monitor the output of tail -F ~/.mysql_history from the manual: --retry ...
1
vote
2answers
736 views

tail -f equivalent

I am seeing a delay of several seconds with the tail command. I found the cause for it has something to do with nfs services. I am using Arch linux and yet to find out how to disable all these ...
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 ...
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.
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 ...
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 ...
8
votes
4answers
10k views

What's an alternative to tail -f that has convenient scrolling? [duplicate]

I'm usually inside GNU Screen or tmux, and that doesn't give me great scrolling functionality. Is there an alternative to tail -f that allows me to quickly scroll up? A tool that is like most is to ...
5
votes
4answers
3k views

Prevent tail from modifying the charset of the terminal

In a Linux terminal (CentOS) I am using the command tail --follow=name my-rolling-file.log in order to see the logs of my application. Sometimes in the log, there is some binary data dumped (I dump ...
7
votes
6answers
5k views

Is it possible to “roll” a symlink to a new file without affecting any open file handles?

An application I am developing locally logs it's output to files formatted with the current timestamp such as app-%Y%m%d.log. To make it simple to be able to tail the current's day log in a terminal ...
7
votes
2answers
1k views

What logic does the command “exec tail -n +3 $0” from grub2 config have?

Creating custom menu entry, got stuck on this command: exec tail -n +3 $0 Tried it in terminal, got weird result, cannot understand, what this command exactly does and why grub needs it. Could you ...
3
votes
5answers
2k views

Only output most recent 10 (or n) lines of a lengthy command output

I have a command that outputs thousands of lines. I actually need these lines in order to see the progress of the command. But I do not need to see more than the 10 most recent lines. How can I do ...
3
votes
1answer
665 views

POSIX head and tail not feature equivalent

The documentation for POSIX tail's -n option says that The origin for counting shall be 1; that is, -n +1 represents the first line of the file, -n -1 the last. So tail -n 10 (used later on the ...
3
votes
2answers
1k views

tail -f, but when the file is deleted and re-created (not appended)

I'm trying to watch for any new output of a log file. Another script (not under my control) is deleting the file then creating a new one with the same name. Using tail -f doesn't work because the file ...
2
votes
4answers
1k views

How to change color of a character while tailing and tr

I regularly use this command line but I would like to change the color of the "|" to green in the output. Does anyone know how I can accomplish this? tail -f file.log | tr '\001' '|' | grep TEST
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 ...
8
votes
3answers
18k views

Suppress 'file truncated' messages when using tail

I'm tailing a log file using tail -f messages.log and this is part of the output: Lorem ipsum dolor sit amet, consectetur adipiscing elit. Fusce eget tellus sit amet odio porttitor rhoncus. Donec ...
4
votes
0answers
220 views

Combing head and tail in a single call via pipe [duplicate]

On a regular basis, I am piping the output of some program to either head or tail. Now, suppose that I want to see the first AND last 10 lines of piped output, such that I could do something like ./...