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Showing What's in a File
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25.18 Watching Several Files Grow

Now here's a useful tool: suppose you want to monitor several files at once. Administrators, for example, might want to keep track of several log files, such as /usr/adm/messages , /usr/adm/lpd-errs , UUCP error files, etc.

xtail
The xtail program comes in useful for keeping an eye on several administrative log files at once. But it also comes in useful for non-administrators. It's sort of a tail -f   for several files as once.

For example, suppose you want to perform several grep s through many files, saving the output in different files. You can then monitor the files using xtail . For example:

% grep Berkeley ch?? > Berkeley.grep &


% grep BSD ch?? > BSD.grep &


% grep "System V" ch?? > SystemV.grep &


% grep SysV ch?? > SysV.grep &


% xtail Berkeley.grep BSD.grep SystemV.grep SysV.grep

When new text appears in the files called with xtail , it also appears on the screen:

*** SysV.grep ***
ch01:using a SysV-based UNIX system, you must

*** Berkeley.grep ***
ch01:at the University of California at Berkeley, where

*** BSD.grep ***
ch03:prefer BSD UNIX systems because they are less likely to
ch04:who use a BSD-based UNIX systems must run the

*** SysV.grep ***
ch04:is a SysV derivative sold by Acme Products Inc.

(When text is written to a new file, the filename is printed surrounded by *** .)

If you press your interrupt key (5.9 ) (usually CTRL-c or DEL), xtail will tell you which files have been modified most recently:

[CTRL-c]

*** recently changed files ***
   1   4-Nov-92 18:21:12  BSD.grep
   2   4-Nov-92 18:19:52  Berkeley.grep
   3   4-Nov-92 17:42:45  SysV.grep

To exit xtail , you must send the QUIT signal (usually CTRL-\, control-backslash).

If an argument given to xtail is a directory name and not a filename, then xtail monitors all files in that directory. For administrators, this comes in very useful for monitoring the UUCP (1.33 ) log files in all the subdirectories of /usr/spool/uucp/.Log :

% xtail /usr/spool/uucp/.Log/*

- LM


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