Replace a value in a file

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# 1  
Old 09-17-2011
Replace a value in a file

I have a file with the following line

parameter (nx = 277, ncmk = 377)

I want to write a script where I can replace the current values of of the variables nx and ncmk with new values defined by variables $nx and $ncmk.

# 2  
Old 09-17-2011
perl -i -pe "/parameter/&&s/nx = \d+/nx = $nx/&&s/ncmk = \d+/ncmk = $ncmk/" file

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# 3  
Old 09-17-2011
sed -e "s/\(nx = \)/\1$nx/g" -e "s/\(ncmk = \)/\1$ncmk/g" inputFile > outputFile


---------- Post updated at 03:23 AM ---------- Previous update was at 03:14 AM ----------

Initially I understood your issue incorrectly Smilie. Have corrected the code.

This is what you want right?
parameter (nx = 277, ncmk = 377)
parameter (nx = 123, ncmk = 456)


Last edited by ahamed101; 09-17-2011 at 08:22 AM..
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# 4  
Old 09-17-2011
Many thanks bartus11, that worked like a charm!

Yes ahamed101 that's what I meant. The your bit of code just appends the new values next to the old ones, i.e. it doesn't replace the old values?
# 5  
Old 09-17-2011
Try this

sed -e "s/\(parameter (nx = \).*\(, ncmk = \).*\()\)$/\1$nx\2$ncmk\3" inputFile > outputFile

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# 6  
Old 09-18-2011
Hi I have another problem of the similar type. This time the line where the value I want to change looks like

Open (unit=Lfile1, file='Nc_957.dat')

I want to replace the number 957 with a variable $nc. I don't know anything about regex to achieve this.

Also the other problem the above line occurs three times in my file, but I only want the change to be in the third occurrence or the 48th line. I guess it's not ideal if I define the line in case I add more lines of code.


---------- Post updated at 03:52 PM ---------- Previous update was at 11:51 AM ----------

I've made some progress the following code does what I want

perl -i -pe "/Open/&&s/Nc_\d+/Nc_$nx/" test.f

But how can I do this on say the nth line rather than every line it occurs?

Last edited by lost.identity; 09-18-2011 at 01:09 PM..
# 7  
Old 09-18-2011
This will replace every 3rd occurrence of the Open line:
perl -i -pe "(++\$i%3==0)&&/Open/&&s/Nc_\d+/Nc_$nx/" test.f

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