Grep Show Lines Before and After

The short answer

To show N lines before and after the grep results, including the lines containing the matched search pattern, you can use the -C flag (short for context) as follows:

 $ grep -C <number> <pattern> <file>

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For example, to show 3 lines:

$ grep -C 3 "pattern" file.txt

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Read our article on how to grep across multiple lines if you are trying to provide a multi-line grep input.

Easily retrieve this command using Warp’s AI Command Search

If you’re using Warp as your terminal, you can easily retrieve this command using the Warp AI Command Search feature:

Entering grep show context lines in the AI Command Search will prompt a grep command that can then quickly be inserted into your shell by doing CMD+ENTER.

Showing N lines before the grep result

$ grep -B  <number>  <pattern>  <file>

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For example, to show 3 lines:

 $ grep -B 3 "pattern" file.txt

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Showing N lines after thegrep result

To show N lines after the grep results, including the lines containing the matched search pattern, you can use the -A flag (short for after) as follows:

 $ grep -A <number> <pattern> <file>

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For example, to show 3 lines:

 $ grep -A 3 "pattern" file.txt

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Selectively showing N lines before and after the grep result

To selectively show N lines before and M lines after the grep results, including the matched search pattern, you can use a combination of the aforementioned -B and -A flags.

For example, to show 1 line before and 2 lines after:

$ grep -B 1 -A 2 "pattern" file.txt

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Showing all lines before the grep result

To show all lines before the grep results, not including the search pattern, you can use a combination of the following commands:

$ head -n $(( $(grep -m <number> -n <pattern> <file> | tail
-n 1 | cut -d ':' -f 1) - 1 )) <file>

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Where:

• head -n displays the first N lines of a file.
• grep -m <number> -n <pattern> <file> searches for the pattern in the file and returns the line number and corresponding lines where the pattern is found. The -m option flag tells grep to stop after finding number matches—leave it out if you want to find all matches.
• tail -n 1 displays the last line of the matches returned by grep
• cut -d ':' -f 1 returns the line number of the pattern matched by grep.
• $( … ) is used to substitute a command by the result of its execution.
• $(( … )) is an expansion used to perform arithmetic calculations.

For example, considering the following file:

$ cat lorem.txt
sed ut perspiciatis
unde omnis iste natus
ut labore et dolore
sed quia consequuntur
qui ratione voluptatem
neque porro quisquam
sed quia non numquam

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The following command will attempt to display all the lines of the lorem.txt file before the one containing the second matched sed pattern.

$ head -n $(( $(grep -m 2 -n "sed" lorem.txt |
  tail -n 1 | cut -d ':' -f 1) - 1 )) lorem.txt

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Which will output:

sed ut perspiciatis
unde omnis iste natus
ut labore et dolore

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Common pitfalls

Note that when using the -m 1 flag, if the pattern matched by grep is present in the first line of the file, this command will output the following error indicating that the head command cannot print the first 0 lines of the specified file.

head: illegal line count -- 0

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Also note that, if the searched pattern doesn’t exist in the specified file, this command will output the following error message.

head: illegal line count -- -1

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Showing all lines after the grep result

To show all lines after the grep result, not including the search pattern, you can use a combination of the following commands:

$ tail -n $(( $(wc -l < < file> | tr -d ' ') - $(grep -m <number> -n <pattern> <file> |
  tail -n 1 | cut -d ':' -f 1)  )) <file>

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Where:

• tail -n displays the last N lines of a file.
• wc -l returns the number of lines of the specified file.
• tr -d ' ' removes space characters from the string returned by wc.
• cut -d ':' -f 1 returns the line number of the pattern matched by grep.
• $( … ) is used to substitute a command by the result of its execution.
• $(( … )) is an expansion used to perform arithmetic calculations.

For example, considering the following file:

 
$ cat lorem.txt
sed ut perspiciatis
unde omnis iste natus
ut labore et dolore
sed quia consequuntur
qui ratione voluptatem
neque porro quisquam
sed quia non numquam

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The following command will attempt to display all the lines of the lorem.txt file after the one containing the second matched sed pattern.

  
$ tail -n $(( $(wc -l < lorem.txt | tr -d ' ') - $(grep -m 2 -n "sed" lorem.txt |
  tail -n 1 | cut -d ':' -f 1)  )) lorem.txt

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Will output:

  
qui ratione voluptatem
neque porro quisquam
sed quia non numquam

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Common pitfalls

Note that, if the searched pattern doesn’t exist in the specified file, this command will output the following error message.

  
-bash: 7 -   : syntax error: operand expected (error token is " ")

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