Question

I’m new to this, just wondering if anyone could help 🙂

I have a file like this:

start1  
12.3  
13.2  
15.3  
end1

How do I find the string end1 and add a few lines before the string, so it looks like:

start1  
12.3  
13.2  
15.3  
NaN  
NaN  
end1

But the number of line added has to depend on a specific number, say 5. If it only has 3 entries between start1 and end1, the numbers of line added is 2.

Answer 1

It’s really not clear whether that number you mention is always something you figure out from the file contents or something you might program but try this:

awk '
/start/ { c=0 }
/end/   { for (i=1; i<c; i++) print "NaN" }
{ print; ++c }
' file

and let us know of any problems.

EDIT: to add c lines if less than 5 lines exist:

awk '
/start/ { c=0 }
/end/ && c<5  { for (i=1; i<c; i++) print "NaN" }
{ print; ++c }
' file

or to pad up to 5 lines:

awk '
/start/ { c=0 }
/end/   { for (i=c; i<=5; i++) print "NaN" }
{ print; ++c }
' file