Listing installed packages with YUM:

$ sudo yum list installed

To display details about a package:

$ yum info nginx

You can cat all installed packages to a file, copy the file to another machine and duplicate the system:

$ sudo yum list installed > installed-packages.txt $ sudo yum -y install $(cat installed-packages.txt)

List installed packages with RPM:

Let’s say that you want to delete the last 3 commits that you’ve already pushed to the remote repository. In this example, you want 566dab6 to be the new HEAD revision.

$ git log --pretty=oneline --abbrev-commit 57bc36b (HEAD -> master, origin/master, origin/HEAD) 3nd set of bad entries on 6th commit dfb4bd3 2nd set of bad entries on 5th commit 0fd1e16 First set of bad entries on 4th commit 566dab6 Yet more good entries on third commit d50370a More good entries on second commit b5fbc6d Good entries on first commit 2cad4c7 Initial commit

If you have a file (or a stream) that has blank lines you want to remove, you can use this command:

$ grep -v "^ *$" file-with-blanks.txt > output-file.txt

where file-with-blanks.txt is the input file and has blank lines and output-file.txt will be the output file without the blank lines.

You have to keep the space between the ^ and the *$ otherwise blank lines which include spaces will not be removed.

You can use ffmpeg to convert webm to mp4 on the command line very easily:

$ ffmpeg -i file.webm -c copy file.mp4

This will stream copy (re-mux) and avoid re-encoding.

If you use the excellent Bitwarden app for you password storage you may not be aware that they also have a command line version on Linux. It outputs data using the JSON format. You can install the jq JSON parser and pipe the output of the CLI’s query to it in order to extract the username and password for a specific site in your search:

$ bw list items --search accounts.google.com | jq '.[] | .login.uris[].uri,.login.username,.login.password' "https://accounts.google.com" "john.doe@gmail.com" "** password1 **" "https://accounts.google.com" "jdoe@gmail.com" "** password2 **"

Sometimes you may want to move a virtual machine in VirtualBox from one server to another. Once way of doing that is to export it from the command line.

1. Locate the virtual machine that you want to export (I’ll use the name UbuntuServer for the one to be exported and name the new one UbuntuServerNew), and then
2. Run the export command as follows:

$ vboxmanage export UbuntuServer -o UbuntuServerNew.ova

If you have used youtube-dl to download content from YouTube then you know that the file names can get to be rather long. In addition to the video’s title there is a dash followed by what appears to be a random sequence of characters just before the file extension. If you find this to be annoying then here is a code snippet that you can use to remove it.

This will remove the last field separated by a ‘-’ and replace it with the file extension of your choice, .mp4 is used in this example:

If you prefer using mutt as your command line email tool, then here are a couple of examples of using mutt to send emails which can be automated quite easily to use in scripts.

Sending a file attachment (-a) and an empty message body:

$ mutt -s "System Logs" -a /var/log/somelog.log -- username@example.com < /dev/null

Sending a message body using redirection:

$ mutt -s "Email Subject" username@example.com < email.html

Sending a file attachment along with a message body:

Let’s assume that you had a RFC 5822 formatted file named mail.txt as follows:

From: Some Sender <some.sender@gmail.com>
To: Some Recipient <some.recipient@example.com>
Subject: Saying Hello
Date: Tue, 6 Jun 2023 04:15:06 -0100
Message-ID: <1234@local.machine.example>

This is a message just to say hello.
So, "Hello".

You can forward this to a email recipient using Google’s SMTP with the following curl command provided you have a Google app password:

$ curl --url 'smtps://smtp.gmail.com:465' --ssl-reqd \
 --mail-from 'some.sender@gmail.com' \ 
 --mail-rcpt 'some.recipient@example.com' \
 --upload-file mail.txt \
 --user 'some.sender@gmail.com:your-gmail-app-password'

Output should be something like this:

You can use netcat to transfer a file from one machine to another machine. On the receiving machine enter the following command:

$ netcat -l 12345 > file.txt or

$ netcat -l -p 12345 > file.pdf

Then, on the sending machine use this command:

$ netcat $MY_IP_ADDRESS 12345 < file.txt