Use “dG” command, if you want to delete all lines in a file starting from the line under the cursor in vi.
Additional commands to delete lines
Command parameters for varnishlog to view the backend server that is processing the request. In this particular case, I wanted to see the request URL and backend server for any responses with HTTP code 401 (unauthorized access)
sudo varnishlog -i BackendOpen,BereqURL -q "BerespStatus == 401"
Just for my records
grep "WORD\|ANOTHER\|NEITHER" string
searches for either “WORD” or “ANOTHER” or “NEITHER” in string.
If you are using a Linux system that uses yum for package management (like Fedora, Centos, RHEL), you can use the following command to find out which package contains a file. This is useful when you want to figure out which package to install. For example, dig (DNS utility) doesn’t come pre-installed on the system. And running “sudo yum install dig” doesn’t do anything.
sudo yum whatprovides '*/dig'
This returns
Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile 32:bind-utils-9.8.2-0.47.rc1.el6.x86_64 : Utilities for querying DNS name servers Repo : base Matched from: Filename : /usr/bin/dig
breaking down the command options
whatprovides : Is used to find out which package provides some feature or file. Just use a specific name or a file-glob-syntax wildcards to list the packages available or installed that provide that feature or file.
We were trying to modify some ACL (access control lists) in squid to allow traffic to certain websites. Instead of adding each individual hostnames in a domain, we wanted to add all traffic to a certain domain.
Document on the interwebs is old or not clear on how to achieve this.
After some trial and error, here is what works
say you want to allow all traffic to the google.com domain, you create a access list using dstdomain like below
acl name_of_acl dstdomain .google.comThe “.” before the domain name acts as a wildcard
Then you use the acl to allow http access to it like below
http_access allow name_of_aclquick note for self
hdparm -tT /dev/sdx
sdx : actual device you want to test
Quick how to on using awk to filter results if a certain value (column) is larger than a set value.
For example, if you have a file (servers.txt) with lines in this format
a_datacenter, servers 20 error, servers xyz b_datacenter, servers 21 c_datacenter, servers 50
and you want to show only the lines that have server value larger than 20, you can do this in awk by running
grep datacenter servers.txt | awk '$3 > 20 {print ;}' | more
breaking down the commands
grep – parsing down the output to just show the lines containing datacenter
awk – $3 > 20 : Get the third variable (awk seperates text using spaces by default) and check if it is greater than 20
print – print the entire line
The title pretty much says it all :). Here is a quick one liner, using multiple tools, to look for files in a directory, search for certain content in them and replace them with other content
[code]find -type f | xargs grep -l ORIGINAL_CONTENT | xargs perl -p -i -e ‘s/ORIGINAL_CONTENT/NEW_CONTENT/g’ [/code]
You can theoretically take out the grep (second command) and directly pipe the find output to perl and get the same outcome.
Going over list of the options used
find
grep
perl