How can I use a shell script to add and replace lines in a file?

abefroman · 12-10-2005, 01:49 AM

How can I use a shell script to replace lines in a file?

I want the script to:
replace
deliver_queue_load_max = 5
with
deliver_queue_load_max = 25
in exim.conf

and replace
Timeout 300
with
Timeout 60
and
KeepAlive Off
with
KeepAlive On
in httpd.conf

added
#RLimitMEM 203961002
#RLimitCPU 240
after
Alias /bandwidth/ /usr/local/bandmin/htdocs/
in httpd.conf

How can I do this?

Thanks in advance

linmix · 12-10-2005, 08:28 AM

sed is the answer to your question.
Find a good tutorial like this short primer and have alook at the man and info pages...

zahadumy · 12-11-2005, 05:33 PM

Quote:

Originally Posted by abefroman

How can I use a shell script to replace lines in a file?

I want the script to:
replace
deliver_queue_load_max = 5
with
deliver_queue_load_max = 25
in exim.conf

and replace
Timeout 300
with
Timeout 60
and
KeepAlive Off
with
KeepAlive On
in httpd.conf

added
#RLimitMEM 203961002
#RLimitCPU 240
after
Alias /bandwidth/ /usr/local/bandmin/htdocs/
in httpd.conf

How can I do this?

Thanks in advance

Take a look here.
Something like

Code:

"sed s/deliver_queue_load_max\ =\ 5/deliver_queue_load_max\ =\ 25/g"

should work. You might need a "\" before "=", I'm not sure about this.

kshkid · 12-17-2005, 02:32 AM

Quote:

Originally Posted by zahadumy

Take a look here.
Something like

Code:

"sed s/deliver_queue_load_max\ =\ 5/deliver_queue_load_max\ =\ 25/g"

should work. You might need a "\" before "=", I'm not sure about this.

you neednot prefix a "\" before "="
it would work without that

Code:

echo "deliver_queue_load_max = 5" | sed -e 's/deliver_queue_load_max = 5/deliver_queue_load_max = 25/'

linmix · 12-17-2005, 03:22 AM

Have you checked that? Actually the \ is not for = but to escape the white-space.

zahadumy · 12-17-2005, 07:34 AM

Quote:

Originally Posted by linmix

Have you checked that? Actually the \ is not for = but to escape the white-space.

As far as I know, \ is used to escape any character that the shell would construe and you want it construed by the sed command. I'm pretty sure about that...

linmix · 12-17-2005, 08:01 AM

yes, but have a look at the placing. In both cases where \ is use it is located before a space, so in this instance it is not = that's being escaped, but the spaces.

bigearsbilly · 12-19-2005, 05:21 AM

Code:

#!/usr/bin/perl -wna

# splits into an array, -1 is the last field

$F[-1] = "XXX" if m/Timeout/;
$F[-1] = "XXX" if m/KeepAlive/;
$F[-1] = "XXX" if m/deliver_queue_load_max/;

# you get the idea?


print "@F\n" ;

perl -i.bak <script> <file>
will edit the file and create a backup .bak

denver1980 · 12-19-2005, 05:31 AM

You only need to use \ before "system" caracters if you don't want sed to interpret them...
like :
^ = start of line
$ = end of line
so if you want to replace :
My ^ gives me $$
by :
Hello world

Code:

echo 'My ^ gives me $$' | sed 's/My \^ gives me \$\$/Hello world/'

kshkid · 12-21-2005, 04:01 AM

Quote:

Originally Posted by linmix

Have you checked that? Actually the \ is not for = but to escape the white-space.

yes i had checked that.

its working as i had expected.

why to provide a '\' to escape a white-space character which isnt a special character?

i believe i am right.

jschiwal · 12-27-2005, 05:05 PM

The backslash character isn't needed in your case because the sed expression is contained in single quotes. Suppose the name of the file you were changing was named "http one.conf" in that case you would either need to escape the space, or put the argument in quotes. If the filename contained the "$" character, then you would need either a backslash or single quotes.

All of the whitespace characters and special characters are listed in the bashref manual.