How can i remove multiple lines from a file based on a pattern that spans multiple lines?

Question

I have a text formatted like the following:

2020-05-02
apple
string
string
string
string
string
2020-05-03
pear
string
string
string
string
string
2020-05-03
apple
string
string
string
string
string

Each group has 7 lines = Date, Fruit and then 5 strings.

I would like to delete groups of 7 lines from the file by supplying just the date and the fruit.

So if choose '2020-05-03' and 'pear'

this would remove:

2020-05-03
pear
string
string
string
string
string

from the file, resulting in this:

2020-05-02
apple
string
string
string
string
string
2020-05-03
apple
string
string
string
string
string

The file contains thousands of lines, I need a command, probably using sed or awk to:

Search for date 2020-05-03
Check if string after date is pear
delete both lines and following 5 lines

I know i can delete with sed like sed s'/string//g', however i am not sure if i can delete multiple lines.

Note: Date followed by fruit is never repeated twice so

2020-05-02
pear

would only occur once in the file

How can i acheive this?

sed s'/2020-05-03\npear\n(?:.*\n){5}//' doesn't seem to work, but doesn't throw an error — Jonny P
– Jonny P, Commented Feb 5, 2020 at 20:54
I'm not a sed expert but maybe it doesn't support non-capturing groups so try 2020-05-03\npear\n.*\n.*\n.*\n.*\n.*\n — MonkeyZeus
– MonkeyZeus, Commented Feb 5, 2020 at 20:55
I think the issue is the \n , it does not match, eg: sed s'/2020-05-03\npear//' does not remove the first 2 lines — Jonny P
– Jonny P, Commented Feb 5, 2020 at 20:57

anubhava · Accepted Answer · 2020-02-05 20:59:38Z

3

Using awk, you may do this:

awk -v dt='2020-05-03' -v ft='pear' '$1==dt{p=NR} p && NR==p+1{del=($1==ft)}
del && NR<=p+6{next} 1' file

2020-05-02
apple
string
string
string
string
string
2020-05-03
apple
string
string
string
string
string

Explanation:

-v dt='2020-05-03' -v ft='pear': Supply 2 values to awk from command line
$1==dt{p=NR}: If we find a line with matching date then store line no in variable p
p && NR==p+1{del=($1==ft)}: If p>0 and we are at next line then set a flag del to 1 if we have matching fruit name otherwise set that flag to 0.
del && NR<=p+6{next}: If flag del is set then skip next 6 lines
1: Default action to print line

answered Feb 5, 2020 at 20:59

anubhava

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Comments

potong · Accepted Answer · 2020-02-09 11:49:24Z

0

This might work for you (GNU sed):

sed '/2020-05-03/{:a;N;s/[^\n]*/&/7;Ta;/^[^\n]*\npear/d}' file

If a line contains 2020-05-03 gather up in total 7 lines and if the 2nd of these lines contains pear delete them.

answered Feb 9, 2020 at 11:49

potong

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