使用sed或awk用另一个文件的文本替换文本文件的行

Question

I have a text file eg File1.txt and I want to replace its few lines with new lines available in another text file eg File2.txt. The format of File1.txt is as below It has pointers start and end.

START

line 1
line 2
line 3 
line 4
line 5

END

I want to change line 1 to line 5 with the lines available in File2.txt. The number of lines are not equal in File1.txt and File2.txt. File2.txt may have more or less lines as in File1.txt.

I need input from someone. Thanking in anticipation

Answer 1

If the parts of File1.txt that you want to preserve are fixed, you only need to print the second file and include that parts:

printf 'BEGIN\n\n%s\n\nEND\n' "$(<File2.txt)"

IF that's not the case (substitute START/END with the patterns that match the parts that you want to preserve):

awk 'NR == FNR {
  f2 = f2 ? f2 RS $0 : $0
  next
  }
/START|END/ || !NF {
  print; next  
  }
NF && !c++ { 
  print f2 
  }' File2.txt File1.txt

Answer 2

This GNU sed one liner might work:

sed -re '/^START/,/^END/{/^START/{p;r File2.txt' -e '};/^END/p;d}' File1.txt

This inserts File2.txt between START and END but doesn't preserve empty lines after line 1 and before line 2

This tries to preserve empty lines:

sed -re '/^START/,/^END/{//!{/^$/{p;d};x;/./{x;d};x;h;r File2.txt' -e ';d};x;s/.*//;x}' File1.txt