Replace a value in a file

Shell Programming and Scripting
1

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.

Thanks.

2

Try:

perl -i -pe "/parameter/&&s/nx = \d+/nx = $nx/&&s/ncmk = \d+/ncmk = $ncmk/" file
1 Like
3 
nx="whatyouwant"
ncmk="whateveryouwant"
sed -e "s/\(nx = \)/\1$nx/g" -e "s/\(ncmk = \)/\1$ncmk/g" inputFile > outputFile

--ahamed

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

Initially I understood your issue incorrectly :wall:. Have corrected the code.

This is what you want right?

#Input
parameter (nx = 277, ncmk = 377)
 
Ouput
parameter (nx = 123, ncmk = 456)

--ahamed

1 Like
4

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

Try this

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

--ahamed

1 Like
6

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.

Thanks

---------- 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?

7

This will replace every 3rd occurrence of the Open line:

perl -i -pe "(++\$i%3==0)&&/Open/&&s/Nc_\d+/Nc_$nx/" test.f
1 Like
8 
root@bt:/tmp# cat f
     1  Open (unit=Lfile1, file='Nc_957.dat')
     2  Open (unit=Lfile1, file='Nc_957.dat')
     3  Open (unit=Lfile1, file='Nc_957.dat')
     4  Open (unit=Lfile1, file='Nc_957.dat')
     5  Open (unit=Lfile1, file='Nc_957.dat')
     6  Open (unit=Lfile1, file='Nc_957.dat')
     7  Open (unit=Lfile1, file='Nc_957.dat')
     8  Open (unit=Lfile1, file='Nc_957.dat')
     9  Open (unit=Lfile1, file='Nc_957.dat')
    10  Open (unit=Lfile1, file='Nc_957.dat')

root@bt:/tmp# awk -v nc="123" '/file=.Nc_/{++i} {if(i==3){i=0; gsub(/Nc_[0-9]*.dat/,"Nc_"nc".dat")}}1 ' f
     1  Open (unit=Lfile1, file='Nc_957.dat')
     2  Open (unit=Lfile1, file='Nc_957.dat')
     3  Open (unit=Lfile1, file='Nc_123.dat')
     4  Open (unit=Lfile1, file='Nc_957.dat')
     5  Open (unit=Lfile1, file='Nc_957.dat')
     6  Open (unit=Lfile1, file='Nc_123.dat')
     7  Open (unit=Lfile1, file='Nc_957.dat')
     8  Open (unit=Lfile1, file='Nc_957.dat')
     9  Open (unit=Lfile1, file='Nc_123.dat')
    10  Open (unit=Lfile1, file='Nc_957.dat')

--ahamed

1 Like