line1Let's say I want to retrieve the 'random text' lines but have no clue of what it looks like. I however know that the previous line contains the unique 'some text' string and that the line just after the random text I want to retrieve contains the unique 'other text' string.
Note the previous and next lines can contain any other text on them as long as I have a pattern I can match with grep.
Here is how I solve that problem;
Find the pattern before and return it with 999999 lines after
grep 'some text' -A 999999
Remove the first line of the previous results (start at line two)
tail -n +2
Find the pattern following our random text and return it with 999999 lines before it
grep 'other text' -B 999999
Skip the last line of these results
head -n -1
Put together we get
cat file.txt | grep 'some text' -A 999999 | tail -n +2 | grep 'other text' -B 999999 | head -n -1