grep -A until a string

Question

assuming that we have a file containing the following:

chapter 1 blah blah
blah num blah num
num blah num blah
...
blah num
chapter 2 blah blah

and we want to grep this file so we take the lines from chapter 1 blah blah to blah num (the line before the next chapter).

The only things we know are

the stating string chapter 1 blah blah
somewhere after that there is another line starting with chapter

a dummy way to do this is

grep -A <num> -i "chapter 1" <file>

with large enough <num> so the whole chapter will be in it.

`grep -A 999 string1 | grep -B 999 string2` – Mark Setchell Mar 21 '15 at 09:11 — Mark Setchell, Mar 21 '15 at 09:11

score 2 · Answer 1 · answered Mar 21 '15 at 09:06

2

sed -ne '/^chapter 1/,/^chapter/{/^chapter/d;p}' file

answered Mar 21 '15 at 09:06

Cyrus

84,225
14
89
153

See OPs comment. He does not know the number of the next chapter. – Jotne Mar 21 '15 at 09:07

Jotne · Accepted Answer · 2015-03-21T09:11:47.817

1

This is easy to do with awk

awk '/chapter/ {f=0} /chapter 1/ {f=1} f' file
chapter 1 blah blah
blah num blah num
num blah num blah
...
blah num

It will print the line if flag f is true.
The chapter 1 and next chapter to changes the flag.

You can use range with awk but its less flexible if you have other stuff to test.

awk '/chapter 1/,/chapter [^1]/ {if (!/chapter [^1]/) print}' file
chapter 1 blah blah
blah num blah num
num blah num blah
...
blah num

edited Mar 21 '15 at 09:11

answered Mar 21 '15 at 09:01

Jotne

40,548
12
51
55

assuming that the only thing we know is "chapter 1" and that somewhere after that there is a string "chapter" ( we done know the number of it ) ? – Giannis Tzagarakis Mar 21 '15 at 09:03
@GiannisTzagarakis Updated post to use next chapter of any number to stop the output – Jotne Mar 21 '15 at 09:04
just because I want to parse large files, awk seems to be the best solution. It is faster than sed or grep. Thanks! – Giannis Tzagarakis Mar 21 '15 at 09:21
btw, do you know how can pass the number of chapter as a bash script variable? $num=1 awk '/chapter/ {f=0} /chapter $num/ {f=1} f' file (awk -v n=$num '/chapter/ {f=0} /chapter n/ {f=1} f' file) is not working – Giannis Tzagarakis Mar 21 '15 at 10:34
Here is how `awk -v test="$var" '/chapter/ {f=0} $0~"chapter "test {f=1} f' file`. Then just set `var=2` and it will get chapter `2` – Jotne Mar 21 '15 at 14:29

Avinash Raj · Answer 3 · 2015-03-21T09:24:20.883

You could do this through grep itself also but you need to enable Perl-regexp parameter P and z.

$ grep -oPz '^chapter 1[\s\S]*?(?=\nchapter)' file
chapter 1 blah blah
blah num blah num
num blah num blah
...
blah num

[\s\S]*? will do a non-greedy match of zero or more characters until the line which has the string chapter at the start is reached.

From man grep

-z, --null-data           a data line ends in 0 byte, not newline
-P, --perl-regexp         PATTERN is a Perl regular expression
-o, --only-matching       show only the part of a line matching PATTERN

grep -A until a string

3 Answers3

Linked