How to find lines containing a string and then printing those specific lines and something else

command linegrepsed

I use the following command to recursively search multiple files and find the line number in each file in which the string is found.

    grep -nr "the_string" /media/slowly/DATA/lots_of_files > output.txt

The output is as follows:

    /media/slowly/DATA/lots_of_files/lots_of_files/file_3.txt:3:the_string
    /media/slowly/DATA/lots_of_files/lots_of_files/file_7.txt:6:the_string is in this sentence.
    /media/slowly/DATA/lots_of_files/lots_of_files/file_7.txt:9:the_string is in this sentence too.

As shown above, the output includes the filename, line number and all the text in that line including the string.

I have also figured out how to print just the specific lines of a files containing the string using the following command:

    sed '3!d' /media/slowly/DATA/lots_of_files/lots_of_files/file_3.txt > print.txt
    sed '6!d' /media/slowly/DATA/lots_of_files/lots_of_files/file_7.txt >> print.txt
    sed '9!d' /media/slowly/DATA/lots_of_files/lots_of_files/file_7.txt >> print.txt

I created the above commands manually by reading the line numbers and filenames

Here's my question.

Q1a

Is there a way to combine both steps into one command? I'm thinking piping the line number and the filename into sed and printing the line. I'm having a problem with the order in which the grep output is generated.

Q1b

Same as above but also print the 2 lines before and 2 lines after the line containing the string (total of 5 lines)? I'm thinking piping the line number and the filename into sed and printing all the required lines somehow.

Big thanks.

Best Answer

If I am understanding the question correctly, you can accomplish this with one grep command.

For Q1a, your grep output can suppress the filename using -h, e.g.:

grep -hnr "the_string" /media/slowly/DATA/lots_of_files > output.txt

For Q1b, your grep output can include lines preceding and following matched lines using -A and -B, e.g.:

grep -hnr -A2 -B2 "the_string" /media/slowly/DATA/lots_of_files > output.txt

The output will contain a separator between matches, which you can suppress with --no-group-separator, e.g.:

grep -hnr -A2 -B2 --no-group-separator "the_string" /media/slowly/DATA/lots_of_files > output.txt

Note that the output uses a different delimiter for matching lines (:) and context lines (-).

Related Solutions

Pattern Search between specific lines and print line numbers

When working w/ sed I typically find it easiest to consistently narrow my possible outcome. This is why I sometimes lean on the !negation operator. It is very often more simple to prune uninteresting input away than it is to pointedly select the interesting kind - at least, this is my opinion on the matter.

I find this method more inline with sed's default behavior - which is to auto-print pattern-space at script's end. For simple things such as this it can also more easily result in a robust script - a script that does not depend on certain implementations' syntax extensions in order to operate (as is commonly seen with sed {functions}).

This is why I recommended you do:

sed '10,15!d;/pattern/!d;=' <input

...which first prunes any line not within the range of lines 10 & 15, and from among those that remain prunes any line which does not match pattern. If you find you'd rather have the line number sed prints on the same line as its matched line, I would probably look to paste in that case. Maybe...

sed '10,15!d;/pattern/!d;=' <input |
paste -sd:\\n -

...which will just alternate replacing input \newlines with either a : character or another \newline.

For example:

seq 150 |
sed '10,50!d;/5/!d;=' |
paste -sd:\\n -

...prints...

Grep keep (output) entire .txt file if one line contains string

For non-GNU versions of grep, which are unlikely to have -z, or if portability is required...

grep -q pattern file && cat file

-q suppresses any output but, per usual, exit status is set based on whether or not a pattern match was found. With a pattern match grep returns the success code 0 which is equivalent to true and that allows the cat command to be executed.

Best Answer

Related Solutions

Pattern Search between specific lines and print line numbers

Grep keep (output) entire .txt file if one line contains string

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