UNIX for Dummies Questions & Answers

Hi,
I am new to scripting in unix..
Anyway i'll jump straight to the problem that i am facing..
I have a file that, i have to search in the file for some specific data and update it.
For ex..
(a data row in the file)
12345678|abc

what i do is sed 's/\(12345678\).*/\1|cd/' fileName.dat from the unix prompt so that i change this row in the file to:
12345678|cd
running this command from the prompt gives me an output on the console and the row is indeed changed, but if i open the file then the row is still the same as was before the change!!!!..
i tried sed 's/\(12345678\).*/\1|cd/g' fileName.dat as well but the same result. i tried to run chmod 777 filename.dat and chmod +rwx filename.dat, before i ran the command, but the same result, i also tried to pipe the command in the following way:
sed 's/\(12345678\).*/\1|cd/' fileName.dat | >[fileName.txt]|mv fileName.txt fileName.dat
but this results in an an empty fileName.dat file!!!!!!!!!!!!!!!!!

Can someone help me on this please, i am not a unix programmer, i have scripted only as much to run a set of commands in one go (move to directory, find a file, run a shell script etc)..
i have not used ksh scripting to process data files before....

Please let me know, many thanks in advance....
Am

It's not the default of sed to save the changes to the file, you can use the -i option if your sed version supports that:

Code:

sed -i 's/\(12345678\).*/\1|cd/' fileName.dat

Use a temporary file otherwise:

Code:

sed 's/\(12345678\).*/\1|cd/' fileName.dat > fileName.new
mv fileName.new fileName.dat

Regards

Hi..thank you so much for your reply....

looks like the '-i' option is not supported the version we are using will use the temporary file option instead..
Also could you let me know if there is any change in behaviour for the sed command, if run from a script and if i were using variables from within the loop..that is to say if i were using it as below[actually this is what i am trying to do..heh]

cut -f1 -d "|" SomeOtherFileName.dat | while read rec
[some if condition that matches the number read in the loop]
then
sed 's/\($rec*\).*/\1|cd/' FileName.dat
else
echo 'bbye'

the rec is a variable of the while loop inside that is an 'if' condition inside of which i am trying to make this update happen!
I ask this because, sed is not changing/updating the data as it is supposed to, and as it does if i use that with absolute values from the unix prompt!!It is sending the output to the console and i can see the change is not happening..
Thanks again..
Am

oh, i used double quotes in the command instead of the single quotes, and it's worked as supposed to....

Thanks a lot....
Am