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

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58
votes
6answers
101k 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 /...
152
votes
18answers
85k 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 ...
51
votes
1answer
11k 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 ...
21
votes
3answers
23k 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 ...
20
votes
9answers
41k 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. ...
12
votes
1answer
881 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 ...
88
votes
3answers
5k 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.
18
votes
6answers
3k 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.
6
votes
2answers
1k 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 ...
4
votes
2answers
3k 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 ...
42
votes
4answers
92k 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 ...
34
votes
8answers
18k 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 ...
28
votes
3answers
33k 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 ...
19
votes
5answers
15k 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 ...
16
votes
4answers
3k 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. ...
9
votes
4answers
7k 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 ...
4
votes
1answer
1k 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
894 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 ...
6
votes
1answer
1k 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 ...
14
votes
3answers
5k 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 ...
3
votes
2answers
253 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: --...
1
vote
2answers
503 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 ...
20
votes
6answers
20k 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 ...
17
votes
7answers
19k 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.
10
votes
3answers
1k 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 ...
5
votes
2answers
12k 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 ...
4
votes
5answers
1k 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 ...
4
votes
6answers
3k 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 ...
4
votes
3answers
9k 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: ...
3
votes
1answer
346 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 ...
2
votes
4answers
663 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
11
votes
2answers
377 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 ...
4
votes
0answers
83 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 ./...
3
votes
2answers
2k views

Using tail to follow daily log file in Bash

I have a task to use a bash script to monitor a couple of log files named with the current day, eg. YYYY-MM-DD.log. (1) I used tail -f to follow the file but unable to deal file rotation. Even if ...
3
votes
1answer
141 views

Why are some file changes not shown in tail -f?

I tried to follow the mysql history file with: tail -f ~/.mysql_history in another window I entered as the same user: mysql -u someotheruser -p and none of the following commands are shown in my ...
1
vote
1answer
4k views

how do i redirect output from tailf & grep to a file [duplicate]

All I wanted is to grep for specific lines in an ongoing log and re-direct it to some file.. tailf log | grep "some words" Now, I want the above command output to get re-directed to some file in on-...
0
votes
0answers
65 views

Why does GNU head/tail read the whole file? [duplicate]

I have a huge file and want to see its beginning and end. However, when I use head and tail, it apparently tries to read the whole file. Since the file is larger than a terabyte, this takes a very ...
0
votes
1answer
42 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 ...