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I have two textfiles: file1 and file2, both with several lines.

$ cat file1
line one
line two
line three
line four
line five

$ cat file2
line A
line B
line C
line D
line E
line F

I would like to substitute a range of lines of file1 (from line 1_start to line 1_end) with a range of lines of file2 (from line 2_start to line 2_end).

For example, substitute lines 2,4 in file1 with lines 3,5 from file2.

What I only could do till now is to extract the needed lines from file2 with

$ sed -n 3,5p file2

But it doesn't help putting them in file1. Is it possible with sed? If not, is it possible with a similar tool?

sed can print a given range of lines with something like this:

sed -n 'X,Yp' filename

Where X is first line in a range and Y is the last line, both inclusive. -n tells sed not to print anything unless explicitly told to do so and that's what the p following the range does.

So you can easily call this three times, appending to a temporary file, then move that file to wherever you want. You can also combine them all using cat and process substitution as this example shows (I'm using line numbers I just pulled out of thin air; $ is last line in a file):

cat <(sed -n '1,5p' file1) <(sed -n '10,12p' file2) <(sed -n '9,$p' file1) > file1.tmp && mv file1.tmp file1

Here, we'd be replacing lines 6, 7 and 8 in file1 with lines 10, 11 and 12 from file2.

Update: Thanks to @MiniMax for pointing out that catand the process substitution can be avoided by doing the following:

 sed -n '1,5p' file1; sed -n '10,12p' file2; sed -n '9,$p' file1; > file1.tmp && mv file1.tmp file1

KISS, after all. :)

Another way to do with sed is using r command, handy if -i inplace option has to be used as well

$ sed -n '3,5p; 5q;' f2 | sed -e '2r /dev/stdin' -e '2,4d' f1
line one
line C
line D
line E
line five

$ # if /dev/stdin is not supported
$ sed -n '3,5p; 5q;' f2 > t1
$ sed -e '2r t1' -e '2,4d' f1

Thanks to don_crissti for reminding that we could quit as soon as required line(s) are obtained from file 2.

With huge input files this may be faster:

# replacing lines m1,m2 from file1 with lines n1,n2 from file2

m1=2; m2=4; n1=3; n2=5

 head -n $((m1-1)); head -n $((n1-1)) >/dev/null; head -n $((n2-n1+1));
 <file2; head -n $((m2-m1+1)) >/dev/null; cat; <file1

It's explained here, the only difference being the one-line ranges in that particular case.

I've started doing everything with Python lately, so here's a Python program that does what you want:

#!/usr/bin/env python2
# -*- coding: ascii -*-
"""replace_range.py"""

import sys
import argparse

parser = argparse.ArgumentParser()

parser.add_argument(
 "matchfile",
 help="File in which to replace lines",
)
parser.add_argument(
 "matchrange",
 help="Comma-separated range of Lines to match and replace",
)
parser.add_argument(
 "replacementfile",
 help="File from which to get replacement lines"
)
parser.add_argument(
 "replacementrange",
 help="Comma-separated range of lines from which to get replacement"
)

if __name__=="__main__":

 # Parse the command-line arguments
 args = parser.parse_args()

 # Open the files
 with 
 open(args.matchfile, 'r') as matchfile, 
 open(args.replacementfile, 'r') as replacementfile:

 # Get the input from the match file as a list of strings 
 matchlines = matchfile.readlines()

 # Get the match range (NOTE: shitf by -1 to convert to zero-indexed list)
 mstart = int(args.matchrange.strip().split(',')[0]) - 1
 mend = int(args.matchrange.strip().split(',')[1]) - 1

 # Get the input from the replacement file as a list of strings 
 replacementlines = replacementfile.readlines()

 # Get the replacement range (NOTE: shitf by -1 to convert to zero-indexed list)
 rstart = int(args.replacementrange.strip().split(',')[0]) -1
 rend = int(args.replacementrange.strip().split(',')[1]) - 1

 # Replace the match text with the replacement text
 outputlines = matchlines[0:mstart] + replacementlines[rstart:rend+1] + matchlines[mend+1:]

 # Output the result
 sys.stdout.write(''.join(outputlines))

And here's what it looks like in action:

user@host:~$ python replace_range.py file1 2,3 file2 2,4

line one
line B
line C
line D
line four
line five