What is something *new* you have learned about Linux within the past 7 days?

average_user · 04-22-2021, 03:01 PM

I learned how to use nmcli to connect to 802.1X protected network.

I learned that you can use xrandr to configure 2 monitors connected by the daisy chain as you would normally do.

pinqvin · 04-22-2021, 03:33 PM

I have learned that my (?) Linux distro has a native hash checking utility with many options... Don't need to download and install one separately.

Code:

[sha|md5]sum

Michael Uplawski · 04-23-2021, 06:30 AM

Quote:

Originally Posted by pinqvin

I have learned that my (?) Linux distro has a native hash checking utility with many options.

They are normally different programs. shasum uses to be implemented in Perl, md5sum appears to be a C-program.

Code:

brillat@savarin:~$ man md5sum

Quote:

BUGS

Do not use the MD5 algorithm for security related purposes. Instead,
use an SHA-2 algorithm, implemented in the programs sha224sum(1),
sha256sum(1), sha384sum(1), sha512sum(1), or the BLAKE2 algorithm, im‐
plemented in b2sum(1)

igadoter · 04-24-2021, 08:46 AM

Code:

% command -v ls

ondoho · 04-25-2021, 01:21 AM

^ or

Code:

type ls

igadoter · 04-25-2021, 05:55 PM

Code:

% wget http://remote/file & tail -f wget-log

igadoter · 04-25-2021, 11:35 PM

To test csum (md5um, sha...) on the fly, eg.

Code:

% mkfifo /tmp/csum
% wget -O - http://remote-site/hybrid.iso | tee /tmp/csum | dd of=/dev/sdb & (md5sum /tmp/csum > hybrid.iso.md5)

MadeInGermany · 04-26-2021, 06:55 PM

Let bash do an automatic fifo (or device) by using a "process substitution"

Code:

wget -O - http://remote-site/hybrid.iso | tee >(md5sum > hybrid.iso.md5) | dd of=/dev/sdb bs=1M

Or

Code:

wget -O - http://remote-site/hybrid.iso | tee >(dd of=/dev/sdb bs=1M) | md5sum > hybrid.iso.md5

dogpatch · 04-30-2021, 11:27 AM

Just learned about csplit, thanks to shruggy in the programming forum. Very good to know about this when uploading multiple files in one text file, as is commonly done in the programming forum.

rnturn · 05-02-2021, 12:34 AM

While I was working on a system and wanted a hard copy of a config file to compare to another system's, I discovered that no print queues had ever been set up. And... the CUPS config software crashed while trying to set one up (now I know why no queues). Yes, I could have sftped that config file to another system with a working print queue but that gets old fast -- and I always forget to get rid of those copies -- then I thought: Ah ha! netcat!

Code:

$ cat path-to-file | netcat -C printer-ip-addr 9100

It appears to hang when the above command is issued but when you enter Ctrl-C, the printer kicks into action. No fancy printing (and maybe not duplexed even if the printer supports it) but works in a pinch.

evo2 · 05-06-2021, 08:42 PM

I use the following which allows passing options to the printer. Needs ssh authentication but as with the netcat solution is also just a one liner (no scp, ssh, lpr, rm, exit).

Code:

cat path-to-file | ssh hostwithprintqueue lpr [lpropts]

Evo2.

Chuck56 · 05-15-2021, 02:48 PM

Parameter Expansion in Bash (or probably all major shells) is amazing! I've used some parameter expansion in the past while manipulating text but this week I dove in to learn more. Time well spent!

https://www.gnu.org/software/bash/ma...Expansion.html

Enjoy!

ondoho · 05-15-2021, 11:15 PM

Quote:

Originally Posted by Chuck56

Parameter Expansion in Bash (or probably all major shells) is amazing! I've used some parameter expansion in the past while manipulating text but this week I dove in to learn more. Time well spent!

https://www.gnu.org/software/bash/ma...Expansion.html

Enjoy!

Oh yes!
There's a few I didn't know, esp. the last paragraph "${parameter@operator}".

Just keep in mind that many of these do not translate to other shells, e.g. dash, the default startup shell for Debian systems.

MadeInGermany · 05-16-2021, 12:45 AM

Apropos parameter expansion,
the term parameter means variable aka ${varname} or positional parameter aka ${1} ${2}

The following is from the ksh man page - it is missing in the previously posted URL and in man bash

Quote:

If the colon ( : ) is omitted from the above expressions, then the shell only checks whether parameter is set or not.

What does it mean?
An exercise:

Code:

var="hello"
[ "${var+x}" ] && echo "var exists"
[ "${var:+x}" ] && echo "var is not empty"
var=""
[ "${var+x}" ] && echo "var exists"
[ "${var:+x}" ] && echo "var is not empty"
unset var
[ "${var+x}" ] && echo "var exists"
[ "${var:+x}" ] && echo "var is not empty"

igadoter · 05-16-2021, 06:03 AM

Personally I dislike hello world examples. It is of no use - so one cant easy memorize learned features. I think even difficult examples are better. Not easy to understand them - but once you do - whoooa - that expression of full amazement. And from now on it sits in head. That whoooaaa moment is an anchor.