How to select first occurrence between two patterns including them

Question

How can I select first occurrence between two patterns including them. Preferably using sed or awk.

I have:

text
something P1 something
content1
content2
something P2 something
text
something P1 something
content3
content4
something P2 something
text

I want the first occurrence of the lines between P1 and P2 (including P1 line and P2 line):

something P1 something
content1
content2
something P2 something

Answer 1

sed '/P1/,/P2/!d;/P2/q'

...would do the job portably by deleting all lines which do !not fall within the range, then quitting the first time it encounters the end of the range. It does not fail for P2 preceding P1, and it does not require GNU specific syntax to write simply.

Answer 2

In sed:

sed -n '/P1/,/P2/p; /P2/q'

• -n suppresses the default printing, and you print lines between the matching address ranges using the p command.
• Normally this would match both the sections, so you quit (q) when the first P2 matches.

This will fail if a P2 comes before P1. To handle that case, try:

sed -n '/P1/,/P2/{p; /P2/q}'

Answer 3

with awk

awk '/P1/{a=1};a;/P2/{exit}' file
something P1 something
content1
content2
something P2 something

Answer 4

awk '/P1/,/P2/{print;f=1} f&&/P2/{exit}' data

Quit immediately after print, not before.

Answer 5

If you want to skip the patterns themselves, here is the awk version:

awk '/P2/ {exit} /P1/ {f=1; next} f' file

Answer 6

A simpler awk solution (sort-of halfway between iruvar’s answer and muru’s answer, but not using a variable):

awk '/P1/,/P2/ { print }  /P2/ { exit }'

and, as muru noted, if the first P2 appears before the first P1, this will print nothing.

Of course, if you want to print all the P1-P2 ranges:

something P1 something
content1
content2
something P2 something
something P1 something
content3
content4
something P2 something

just leave out the exit part:

awk '/P1/,/P2/ { print }'

Answer 7

To skip the patterns themselves, and show only first matching block in single GNU sed:

sed -nre '/STARTPATTERN/ {:a;n;/ENDPATTERN/{b;};p;ba}' file

Answer 8

awk '/something P1/{f=1}/something P2/{f=0;print;exit}f'  file

output

something P1 something
content1
content2
something P2 something

Answer 9

sed: (from @SU3's comment):

sed -n '/P1/,${p;/P2/q}'

awk:

awk '/P1/,0 {print; if ( /P2/ ) exit}' file

Both take the same approach: Within the range /P1/ to end of input, print and then exit if P2 is matched.

Both are DRY. P1 and P2 are specified only once.

Both pass the corner case of P2 preceding P1.

Answer 10

Using Raku (formerly known as Perl_6)

raku -ne 'state $i=0; .put if m/ P1 {last if $i++ == 1} /fff/ P2 /;'

#OR

raku -e 'my $i=0; .put if m/ P1 {last if $i++ == 1} /fff/ P2 / for lines;' 

#OR

raku -e 'my $i=0; for lines() { .put if m/ P1 {last if $i++ == 1} /fff/ P2 / };'  

Sample Input:

text
something P1 something
content1
content2
something P2 something
text
something P1 something
content3
content4
something P2 something
text

Sample Output (1):

something P1 something
content1
content2
something P2 something

The above answer is coded in Raku, a member of the Perl-family of programming languages. Explaining the first answer briefly, Raku's non-autoprinting -ne command line flags are employed to run code over each line of input. Raku's m/<start>/fff/<stop>/ sed-like "flip-flop" operator is employed which takes linewise input (special-cased within the Rakudo compiler), enabling the return of text blocks that start with the first matching line and stop with the second matching line. The variable $i is stated once at the beginning of the loop to equal 0 zero. Finally, Raku also allows code blocks to execute within Regexes upon matching.

Putting it all together, when the sed-like "flip-flop" operator encounters a full match in both (start,stop) halves of the fff regex operator, $i gets incremented to 1, and thus lasts out of the loop, so only the first complete match is put. [If you want to output all matches, simply omit the {last if $i++ == 1} code block].

Note, it's simple enough to omit the two 'sentinal' lines in the return by changing fff to ^fff^, giving the following result:

Sample Output (2):

content1
content2

Further testing: All code above handles the case where P2 comes before P1. Additionally, all code above handles the case where P1 and P2 occur on the same line, WITHOUT terminating prematurely. If such "single line text blocks" are desired/preferred in the output, use Raku's "non-sed-like" ff operator instead of the fff operator.

https://docs.raku.org/routine/fff
https://raku.org