Ubuntu – grep to return Nth and Mth lines before and after the match

awkcommand linegrep

I know that with grep I can use the fields -A and -B to pull previous and next lines from a match.

However they pull in all lines between the match based on however many lines are specified.

grep -r -i -B 5 -A 5 "match"

I'd like to only receive the 5^th line before a match and the 5^th line after the match in addition to the matched line and not get the lines between.

Is there a way to do this with the grep?

Best Answer

The tool you want to use is called sift. This is basically a grep on steroids. Grep in parallel. Sift has a huge amount of options to do exactly what you want - specifically to return a particular line relative to a match(s) which may/may not be followed by /preceded by some text.

It amazes me that sift is not mainstream gnu as it was written in the go language but installs on Linux just fine. IT searches in parallel using all cpus huge quantities of text where grep just takes weeks to do the same.

Sift website - see examples

Related Solutions

Ubuntu – How to include a space character with grep

Make sure you quote your expression.

$ grep ' \.pdf' example
grep .pdf

Or if there might be multiple spaces (we can't use * as this will match the cases where there are no preceding spaces)

grep ' \+\.pdf' example

+ means "one or more of the preceding character". In BRE you need to escape it with \ to get this special function, but you can use ERE instead to avoid this

grep -E ' +\.pdf' example

You can also use \s in grep to mean a space

grep '\s\+\.pdf' example

We should escape literal . because in regex . means any character, unless it's in a character class.

Grep – How to Show All Lines Before a Match

Including the match,
```
sed '/foo/q' file
```
It is better to quit sed as soon as a match is found, otherwise sed would keep reading the file and wasting your time, which would be considerable for large files.
Excluding the match,
```
sed -n '/foo/q;p' file
```
The -n flag means that only lines that reach the p command will be printed. Since the foo line triggers the quit action, it does not reach p and thus is not printed.
- If your sed is GNU's, this can be simplified to
```
sed '/foo/Q' file
```

References

Best Answer

Related Solutions

Ubuntu – How to include a space character with grep

Grep – How to Show All Lines Before a Match

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