How to use tail -f with grep to show surrounding lines

greptail

I would like to see the output in a logfile greped by only one domain but also the following two lines.

Example:

tail -f /var/log/apache2/modsec_audit.log |grep mydomain.de

this shows all lines, that contain "mydomain.de" but the important information is in the line below the line, where the domain is included

Best Answer

grep has extra options to define how many lines before and after the result:

-A (after)
-B (before)
-C (context [before + after])

So in your case you need -A:

YOUR_COMMAND |grep -A NUMBER YOURDOMAIN

the above command prints NUMBER of lines after YOURDOMAIN in file.

Related Solutions

Display lines inbetween text with grep

Here is a sed call to get everything between (and including) two specific strings:

sed -n '/<VirtualHost*/,/<\/VirtualHost>/p' httpd.conf

If you want to search for a specific domain, just add it:

sed -n '/<VirtualHost 192.168.1.10:80>*/,/<\/VirtualHost>/p' httpd.conf

How to grep a line with unknown number of its indented lines

If you want to output a REGEXP match and all the indented lines that are just after the match:

command | perl -ne '/^( *)/; $i = length $1; $j && $i >= $j and print, next; $j = 0; /REGEXP/ and $j = $i + 1, print'

replacing REGEXP by your regular expression.

For instance,

$ perl -ne '/^( *)/; $i = length $1; $j && $i >= $j and print, next; $j = 0; /a/ and $j = $i + 1, print' <<EOF
a
b
  c
  a
    b
    a
    c
      b
    d
  e
    b
  a
    c
e
EOF

outputs:

Best Answer

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Display lines inbetween text with grep

How to grep a line with unknown number of its indented lines

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