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Re: Command "tail" printing of '\b' and '\t' Characters

From: Bob Proulx
Subject: Re: Command "tail" printing of '\b' and '\t' Characters
Date: Wed, 5 Sep 2001 18:42:41 -0600


> A program that reproduces the problem follows these directions.
> Copy the source to a file called tail.c.

You are writing to the syslog daemon.  It turns out there is a command
line program to do that called 'logger' which can make this a little
easier to demonstrate.  But I digress.

> tail -f /var/log/messages
> Sep  5 13:51:05 mrx kernel: ^IThe back space and tab characters show up as:
> Sep  5 13:51:05 mrx kernel: ^I^I- backspace -> ^H
> Sep  5 13:51:05 mrx kernel: ^I^I- tab       -> ^I
> Sep  5 13:51:16 mrx kernel: tail.c^H^H::cleanup_module() line 34

This is not a bug in tail.  Nor do I think this is a bug in syslog
either.  It is just the way syslog operates.  It is translating
nonprintable characters into printable characters.

The syslogd/logger functionality is cleaning those up and the actual
values in the messages file are printable.  Tail is doing nothing to
them.  If you edit the /var/log/messages file with an editor you
should be able to verify for yourself that the strings were cleaned up
before tail read them.


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