unix command to get lines from in between first and last occurence of a word and write to a file - bash

Question

I want a unix command to find the lines between first & last occurence of a word
For example:
let's imagine we have 1000 lines. Tenth line contains word "stackoverflow", thirty fifth line also contains word "stackoverflow".
I want to print lines between 10 and 35 and write it to a new file.

Answer 1

You can make it in two steps. The basic idea is to:
1) get the line number of the first and last match.
2) print the range of lines in between these range.
$ read first last <<< $(grep -n stackoverflow your_file | awk -F: 'NR==1 {printf "%d ", $1}; END{print $1}')
$ awk -v f=$first -v l=$last 'NR>=f && NR<=l' your_file
Explanation
read first last reads two values and stores them in $first and $last.
grep -n stackoverflow your_file greps and shows the output like this: number_of_line:output
awk -F: 'NR==1 {printf "%d ", $1}; END{print $1}') prints the number of line of the first and last match of stackoverflow in the file.
And
awk -v f=$first -v l=$last 'NR>=f && NR<=l' your_file prints all lines from $first line number till $last line number.
Test
$ cat a
here we
have some text
stackoverflow
and other things
bla
bla
bla bla
stackoverflow
and whatever else
stackoverflow
to make more fun
blablabla
$ read first last <<< $(grep -n stackoverflow a | awk -F: 'NR==1 {printf "%d ", $1}; END{print $1}')
$ awk -v f=$first -v l=$last 'NR>=f && NR<=l' a
stackoverflow
and other things
bla
bla
bla bla
stackoverflow
and whatever else
stackoverflow
By steps:
$ grep -n stackoverflow a
3:stackoverflow
9:stackoverflow
11:stackoverflow
$ grep -n stackoverflow a | awk -F: 'NR==1 {printf "%d ", $1}; END{print $1}'
3 11
$ read first last <<< $(grep -n stackoverflow a | awk -F: 'NR==1 {printf "%d ", $1}; END{print $1}')
$ echo "first=$first, last=$last"
first=3, last=11

Answer 2

If you know an upper bound of how many lines there can be (say, a million), then you can use this simple abusive script:
(grep -A 100000 stackoverflow | grep -B 1000000 stackoverflow) < file
You can append | tail -n +2 | head -n -1 to strip the border lines as well:
(grep -A 100000 stackoverflow | grep -B 1000000 stackoverflow
| tail -n +2 | head -n -1) < file

Answer 3

I'm not 100% sure from the question whether the output should be inclusive of the first and last matching lines, so I'm assuming it is. But this can be easily changed if we want exclusive instead.
This pure-bash solution does it all in one step - i.e. the file (or pipe) is only read once:
#!/bin/bash
function midgrep {
while read ln; do
[ "$saveline" ] && linea[$((i++))]=$ln
if [[ $ln =~ $1 ]]; then
if [ "$saveline" ]; then
for ((j=0; j<i; j++)); do echo ${linea[$j]}; done
i=0
else
saveline=1
linea[$((i++))]=$ln
fi
fi
done
}
midgrep "$1"
Save this as a script (e.g. midgrep.sh) and pipe whatever output you like to it as follows:
$ cat input.txt | ./midgrep.sh stackoverflow
This works as follows:
find the first matching line and buffer in the first element of an array
continue reading lines until the next match, buffering to the array as we go
on each subsequent matches, flush the buffer array to output
continue reading file to the end. If there are no more matches, then the last buffer is simply discarded.
The advantage of this approach is that we only read through the input one time only. The disadvantage is that we buffer everything between each match - if there are many lines between each match, then these are all buffered to memory, until we hit the next match.
Also this uses the bash =~ regular expression operator to keep this pure bash. But you could replace this with a grep instead, if you are more comfortable with that.

Answer 4

Using perl :
perl -00 -lne '
chomp(my #arr = split /stackoverflow/);
print join "\nstackoverflow", #arr[1 .. $#arr -1 ]
' file.txt | tee newfile.txt
The idea behind this is to feed an array of the whole input file in to chunks using "stackoverflow" string to split. Next, we print the 2nd occurrences to the last -1 with join "stackoverflow".