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Shell Programming and Scripting

sed substitution

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# 1  
Old 07-21-2011
sed substitution
Hello,
I have two files. File1 is normal txt file and File2 contains list of line numbers.

e.g. File2:
Code:
3
6
9
.....

I need to replace a character in File1 in lines (taken from File2). For that I am using a "for" loop:
Code:
for i in $(cat File2)
do
  sed "$i s/Y/N/" File1
done

but my files contain million numbers and for loop is taking a long time. can I use a faster approach?

Thanks......
Last edited by Scott; 07-21-2011 at 03:57 PM.. Reason: Please use code tags, and a subject title that better reflects your problem
# 2  
Old 07-21-2011
You can try another way of reading "File2":
Code:
while read i; do
  sed "$i s/Y/N/" File1
done < File2

# 3  
Old 07-21-2011
I already tried but its slower than what I need....

I am trying to create a data file, which will look sonething like:
sed "3;6;9........ s/Y/N/" File1 (by running a for/while loop)
and then will execute this file..... hopefully this wud be faster....
# 4  
Old 07-21-2011
Code:
awk 'NR == FNR {
  nr[$1]; next
  }
NR in nr {
  sub(/Y/, "N")
  }1' file2 file1

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