Replace a line with a number if part of it is matches using sed

I know this is a very simple question and been discussed many times, but I can’t understand where I am doing wrong in my command.

I would like to replace the lines which starts with “It” as 99999. Each row starts with several blank spaces.

infile.txt
     3
     2
     3
     4
  It is not a number = /home/kayan/data
     3
     5
  It is not a number = /home/kayan/data
     4
     5

JavaScript
​x
 
infile.txt     3     2     3     4  It is not a number = /home/kayan/data     3     5  It is not a number = /home/kayan/data     4     5​

I used

sed -i 's/^I/99999/g' infile.txt

JavaScript
 
sed -i 's/^I/99999/g' infile.txt​

But it is not working.

Answer

give this a try:

sed -i 's/^s*It.*/9999/'

JavaScript
 
sed -i 's/^s*It.*/9999/'​

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Answer