Stupid sed question

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2 total messages Started by Alan H. Mintz Fri, 26 Oct 1990 22:29

#1628

Author: Alan H. Mintz
Date: Fri, 26 Oct 1990 22:29

44 lines
1548 bytes

(Hmmm. Hard to tell if this is the right group nowadays :)

I'm trying to write a script to edit the /etc/ttytype file under XENIX. The
idea is to search the file for the line for a given port and alter the
terminal type associated with it. The ttytype file consists of lines
like:

wy60ak	ttya1
svt1210	ttya2
ansi	ttya3

The separator between the fields is a tab character (\011, 0x09). So,

*********************
:
# Edit script

tty='ttya1'
ttytype='vt100n'

line=`fgrep $tty /etc/ttytype`
cat /etc/ttytype | sed "s/$line/$ttytype	$tty/" >tempfile
#		This is a tab -----------^^^^^^

if [ $? -eq 0 ]
then
 mv tempfile /etc/ttytype
fi
***********************

This works great, if the file does not contain another terminal that starts
with ttya1 (like ttya10):

ansi	ttya1
ansi	ttya10

In this case, sed barfs with "command" garbled. What am I missing here ? I 
understand that the problem has to do with sed matching more than one line,
but why doesn't it just (incorrectly) screw up both lines ?
-- 
< Alan H. Mintz             | Voice +1 714 980 1034       >
< Micro-Quick Systems, Inc. | FAX   +1 714 944 3995       >
< 10384 Hillside Road       | uucp:     ...!uunet!mq!alan >
< Alta Loma, CA  91701 USA  | Internet: alan@MQ.COM       >

Re: Stupid sed question

#1630

Author: Paul John Falstad
Date: Sat, 27 Oct 1990 00:30

54 lines
2289 bytes

In article <118@mq.com> alan@mq.com (Alan H. Mintz) writes:
>(Hmmm. Hard to tell if this is the right group nowadays :)
>
>I'm trying to write a script to edit the /etc/ttytype file under XENIX. The
>idea is to search the file for the line for a given port and alter the
>terminal type associated with it. The ttytype file consists of lines
>like:
>
>wy60ak	ttya1
>svt1210	ttya2
>ansi	ttya3
>
>The separator between the fields is a tab character (\011, 0x09). So,

>tty='ttya1'
>ttytype='vt100n'
>
>line=`fgrep $tty /etc/ttytype`
>cat /etc/ttytype | sed "s/$line/$ttytype	$tty/" >tempfile
>#		This is a tab -----------^^^^^^

>This works great, if the file does not contain another terminal that starts
>with ttya1 (like ttya10):
>
>ansi	ttya1
>ansi	ttya10
>
>In this case, sed barfs with "command" garbled. What am I missing here ? I 

When there are two terminals that contain the string ttya1, $line is
being set to "ansi ttya1\nansi ttya10", since the output of fgrep has
two lines.  So sed sees this as its command:

s/ansi ttya1
ansi ttya10/vt100n ttya1/

which is garbled, since the first line has no ending delimiter.  Try
something like this instead:

line=`grep "[TAB]$tty$" /etc/ttytype`
cat /etc/ttytype | sed "s/$line/$ttytype $tty/" >tempfile

or better, replace both lines with:

sed "/[TAB]$tty\$/s/.*[TAB]/$ttytype[TAB]/" /etc/ttytype >tempfile

If you actually have more fields after the tty name, you may have to
change the \$ to another tab.

--
Paul Falstad, pfalstad@phoenix.princeton.edu PLink:HYPNOS GEnie:P.FALSTAD
"Your attention please.  Would the owner of the Baader-Meinhof shoulder-bag
which has just exploded outside the terminal please pick up the white
courtesy phone."

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