Command line tips & tricks

KAGY · 07-03-2014 12:49am

I had edited my post to include this, but I'll repost it here to keep the flow of conversation:-

btw you could add those string of commands into .bashrc as a function.
function mykill () {kill -9 `ps -e | grep "$1" | cut -d' ' -f1`}

partyboy690 · 07-03-2014 12:30pm

KAGY wrote: »

I had edited my post to include this, but I'll repost it here to keep the flow of conversation:-

btw you could add those string of commands into .bashrc as a function.
function mykill () {kill -9 `ps -e | grep "$1" | cut -d' ' -f1`}

Yeah I could do that6, doesn't make too much of a difference because this command is run adhoc as a job on Jenkins.

PrzemoF · 10-03-2014 5:00pm

Those are not typical command line tips, but I hope they are close enough to fit into this thread.

In vim:
:make - This will run the regular old make in the command line for you.
:copen - Opens the quickfix window, to show the results of the compilation
:cw[indow] - Opens the quickfix window only if there is an error.
:cn - Goto the next error in source code.
:cp - Goto the previous error in source code.
:cfirst - Goto the first error in source code.
:clast - Goto the last error in source code.

P.S. All credit goes to the author of [URL="In vim: :make - This will run the regular old make in the command line for you. :copen - Opens the quickfix window, to show the results of the compilation. Opens the window even if there are no errors in compilation. :cw[indow] - Opens the quickfix window only if there is an error. If quickfix window is open and there are now errors, the window is closed. :cn - Goto the next error in source code. :cp - Goto the previous error in source code. :cfirst - Goto the first error in source code. :clast - Goto the last error in source code. how come that I did not know those earlier?? P.S. All credit goes to the author of this blog"]this blog[/URL]

Recondite49 · 10-06-2014 7:29pm

Generate a random number between X and 1 (in this case 10) drawing directly from the pool of random data.

echo "$(od -An -N4 -tu4 /dev/random) % 10 + 1" | bc

You can check available levels of entropy in your system as follows:

cat /proc/sys/kernel/random/entropy_avail

Be advised that checking available levels of entropy in itself uses up entropy.

If you need lots of random numbers, a personal favourite program of mine is randomsound. It uses white noise from your sound card and pipes it straight into /dev/random.

This comes in very handy when trying to generate gpg/SSL keys.

Recondite49 · 10-06-2014 7:32pm

Another nugget I discovered the other day.

A friend of mine had a folder with over one million jpgs inside it. He wanted to know if there was a terminal command which would allow for automatic search and deletion of all images below a certain size (in this case 250kb).

After some judicious googling I saw that this can be done in one line:

find . -name \*.jpg -size -250k -exec rm {} \

This will take some time but at least it's simple.

Dave! · 10-06-2014 8:44pm

syklops · 11-06-2014 12:17am

Dave! wrote: »

Anyone else baffled?

Khannie · 11-06-2014 9:47am

It means "great". Quoting pictures! I'm surprised at you. :P

syklops · 11-06-2014 2:14pm

Khannie wrote: »

It means "great".

News to me.

Quoting pictures! I'm surprised at you. :P

Well if I didnt quote the picture, how would anyone know what I was baffled about?

Khannie · 11-06-2014 3:01pm

syklops wrote: »

News to me.

Have you not seen Breaking Bad??? :eek:

Khannie · 11-06-2014 5:26pm

Today I learned about a program called parallel. It does what you think it would - launches lots of programs in parallel to make use of your lovely, lovely cores. Here's an example:

parallel -j 8 oggenc -- *.flac

Translation:

in parallel, using 8 cores, run oggenc. Each instance of oggenc will be given one of the files after the -- (in this case a flac file). When one finishes, a new one is spawned so 8 are always running in parallel until the jobs are exhausted.

I had put up a script in here to achieve this before, but this is handier.

edit: Encoded a whole album in 14 seconds. Yummy.

syklops · 11-06-2014 6:00pm

Khannie wrote: »

Have you not seen Breaking Bad??? :eek:

Just the first few episodes. Its on my 'to watch' list.

PrzemoF · 18-06-2014 2:48pm

"Save a file as root with your normal user

Sometimes you start to edit a file without noticing that you can’t save it for permissions problems, tee can easily save you in this case, as example:

$ vim /etc/passwd
[:w !sudo tee %]

In vim this means:

:w saves the file
!sudo calls the sudo command
tee redirects vim’s output
% the current file

After this command you’ll have saved successfully your file and can exit safely from the editor."

Source: http://linuxaria.com/pills/linux-terminal-the-tee-command

Recondite49 · 27-08-2014 11:22am

Tillotson · 02-09-2014 11:43pm

Recondite49 wrote: »

Generate a long, random string of X bits :

dd if=/dev/random bs=1 count=X 2>/dev/null | base64 -w 0 | rev | cut -b 2- | rev

e.g

dd if=/dev/random bs=1 count=32 2>/dev/null | base64 -w 0 | rev | cut -b 2- | rev

7X50xEE3Xxjb0DxI7BDhGqig8k2PfZnJflVj0KG/14g

Very useful if you want to generate a secure password, although admittedly difficult to remember!

cat /dev/random | base64 | head -c 10

PrzemoF · 13-10-2014 8:22am

After you execute a command (or shell script) in the background using &, if you logout from the session, the command will get killed. To avoid that, you should use nohup as shown below.

$ nohup ./my-shell-script.sh &

Using at command you can schedule a job to run at a particular date and time. For example, to execute the backup script at 10 a.m tomorrow, do the following.

$ at -f backup.sh 10 am tomorrow

More here: http://www.thegeekstuff.com/2010/12/5-ways-to-execute-linux-command/

PrzemoF · 10-11-2014 1:10pm

bash:
Ctrl-T - transpose 2 previous words in command line
Alt-T - same for letters
Ctrl+_ - undo changes

syklops · 17-11-2014 6:18pm

PrzemoF wrote: »

bash:
Ctrl-T - transpose 2 previous words in command line
Alt-T - same for letters
Ctrl+_ - undo changes

Im on Fedora and its the other way round.

Khannie · 17-11-2014 6:37pm

Almost universally, Ctrl + Alt + T opens a new terminal.

syklops · 17-11-2014 6:47pm

Khannie wrote: »

Almost universally, Ctrl + Alt + T opens a new terminal.

In KDE its CTRL + shift + t.

Johnboy1951 · 17-11-2014 10:48pm

CTRL + shift + t

opens a new tab here (KDE)

PrzemoF · 18-11-2014 11:44am

syklops wrote: »

Im on Fedora and its the other way round.

My mistake. Unfortunately I cannot edit it

Khannie · 18-11-2014 1:15pm

syklops wrote: »

In KDE its CTRL + shift + t.

That's new tab for me.

Stupid, awkward KDE.

Skrynesaver · 18-11-2014 1:48pm

This is about terminal commands, if your Xterm application captures bash commands you should probably remap the keys as [CTRL]-T (transpose letters), is one of the most useful shortcuts out there for the thickfingered clumsy demographic.

syklops · 18-11-2014 2:04pm

Skrynesaver wrote: »

This is about terminal commands, if your Xterm application captures bash commands you should probably remap the keys as [CTRL]-T (transpose letters), is one of the most useful shortcuts out there for the thickfingered clumsy demographic.

By that you mean, most of us.

syklops · 18-11-2014 2:06pm

Khannie wrote: »

That's new tab for me.

Stupid, awkward KDE.

KDE rocks.

Johnboy1951 · 18-11-2014 2:47pm

In KDE it is (at least here

)

Ctrl + shift + t .... for new tab

and

Ctrl + shift + n .... for New window

They are of course easily modified to your own preferences

humbert · 18-11-2014 11:44pm

Khannie wrote: »

Almost universally, Ctrl + Alt + T opens a new terminal.

I think the mileage on almost universally in Linux isn't great.

deconduo · 18-11-2014 11:47pm

humbert wrote: »

I think the mileage on almost universally in Linux isn't great.

Those sort of shortcuts are mainly DE/WM dependant anyway.

jimgoose · 18-11-2014 11:49pm

CTRL-insert/SHIFT-insert is copy/paste in VNC/PuTTY/ESX console on Solaris/AIX/RHEL/SuSE.

Kinet1c · 19-11-2014 12:06am

Ctrl+Alt+t in LXDE too.

PrzemoF · 05-12-2014 11:03am

Create new file or wipe out content of existing file

> file_name

That's how is works:

[przemo@localhost test]$ ls
[przemo@localhost test]$ > file.log
[przemo@localhost test]$ ls -l
total 0
-rw-rw-r--. 1 przemo przemo 0 Dec  5 10:01 file.log
[przemo@localhost test]$ echo "something" > file.log 
[przemo@localhost test]$ ls -l
total 4
-rw-rw-r--. 1 przemo przemo 10 Dec  5 10:02 file.log
[przemo@localhost test]$ > file.log 
[przemo@localhost test]$ ls -l
total 0
-rw-rw-r--. 1 przemo przemo 0 Dec  5 10:02 file.lo

more here: http://www.linuxtechi.com/standard-input-output-error-in-linux/

PrzemoF · 15-07-2015 11:11am

A stack with directories useful for scripting, but also in normal day-to-day command line operations. Basic commands: pushd, popd and dirs (to show the stack)

[przemo@localhost freecad]$ pwd
/home/przemo/fedora/FreeCAD/freecad
[przemo@localhost freecad]$ pushd .
~/fedora/FreeCAD/freecad ~/fedora/FreeCAD/freecad
[przemo@localhost freecad]$ cd /tmp
[przemo@localhost tmp]$ cd /bin
[przemo@localhost bin]$ cd /usr/share/
[przemo@localhost share]$ popd
~/fedora/FreeCAD/freecad
[przemo@localhost freecad]$ pwd
/home/przemo/fedora/FreeCAD/freecad

PrzemoF · 19-08-2015 9:59am

File

cat file_name_here | command arg1 arg2

can be replaced with

< file_name_here | command arg1 arg2

http://www.catb.org/jargon/html/U/UUOC.html

Dante · 19-08-2015 10:15am

I use this in my bashrc to prettify my bash prompt:

PS1='\e[0;35m\[[\u\]\e[0;37m\]@\e[0;32m\]\h]\e[0;37m\]\$\[\e[0m\] '

It will look something like below:
[usernameserver]:

KAGY · 06-10-2015 5:23pm

Can't remember if this was posted before. Actually I must look back over all the posts again.

If you need to do a calculation for an option you can use $((calc))

e.g. mount a partition from a dd disk image

sudo mount -o ro,loop,offset=$((122880*512)) pi_2015-09.dd /media/SD_backup

where the numbers came from fdisk -l

$sudo fdisk -l pi_2015-09.dd
Sector size (logical/physical): 512 bytes / 512 bytes

Device                   Boot  Start     End Sectors Size Id Type
pi_2015-09.dd1        8192  122879  114688  56M  c W95 FAT32 (LBA)
pi_2015-09.dd2      122880 6399999 6277120   3G 83 Linux

quick edit:
to see progress of a dd

watch --interval=10 "sudo kill -SIGUSR1 1234"

where 1234 is the PID from

ps -ef | grep / dd/

there is a space after the last /

Khannie · 26-11-2015 5:55pm

recursive scp slow because of lots of small files?

ssh remotebox -T -o Compression=no -x "tar cf - /remote/path" | tar xf - -C .

or if you want to store it locally as a tarball:

ssh remotebox -T -o Compression=no -x "tar cf - /remote/path" > tarball.tar

or a compressed tarball:

ssh remotebox -T -o Compression=no -x "tar cf - /remote/path" | gzip -c > tarball.tar.gz

I'm working with a lot of routers these days and they don't have the storage or processing power to be tarring up stuff on the device so this works well.

deconduo · 26-11-2015 10:48pm

Khannie wrote: »

recursive scp slow because of lots of small files?

ssh remotebox -T -o Compression=no -x "tar cf - /remote/path" | tar xf - -C .

or if you want to store it locally as a tarball:

ssh remotebox -T -o Compression=no -x "tar cf - /remote/path" > tarball.tar

or a compressed tarball:

ssh remotebox -T -o Compression=no -x "tar cf - /remote/path" | gzip -c > tarball.tar.gz

I'm working with a lot of routers these days and they don't have the storage or processing power to be tarring up stuff on the device so this works well.

You could also use rsync

Hotblack Desiato · 27-11-2015 9:56pm

You need rsync installed at the remote end though, which a router may not have.

Khannie · 02-12-2015 3:56pm

deconduo wrote: »

You could also use rsync

It's not on the router.

Does it not suffer the same painfully slow multi-file copy issue that SCP does though? It's a while since I've used rsync.

RebelButtMunch · 27-01-2016 11:28am

Want to answer 'n' to lots of repetitive questions? Use the YES command
e.g.
"yes n | gzip -d *"

RebelButtMunch · 27-01-2016 11:28am

Want to answer 'n' to lots of repetitive questions? Use the YES command
e.g.
"yes n | gzip -d *"

RebelButtMunch · 27-01-2016 11:29am

cat a file backwards... use tac command

Keplar240B · 23-06-2016 6:47pm

cat /dev/urandom

https://en.wikipedia.org/wiki//dev/random

Dero · 03-08-2016 10:45am

One thing that (irrationally) bugs me is seeing "grep -v grep"; e.g.

ps -ef | grep java | grep -v grep

So I use this character class trick that someone showed me years ago:

ps -ef | grep [j]ava

It'll also work anywhere else that regex can be used, like awk:

ps -ef | awk '/[j]ava/ {print $2}'

Yes, pgrep will do this, but I work a lot on AIX, which doesn't have pgrep.

Also, for parallel execution, you can use xargs and nproc if parallel is not installed/available.

ls -1 *.flac | xargs -P $(nproc) -n1 -I{} oggenc "{}"

Using nproc will match the number of logical CPUs in your machine, but you could use more or less if you want.

PrzemoF · 19-01-2017 5:15pm

$ cat a
A
B
C
D
$ cat b
1
2
3
4
$ paste a b
A   1
B   2
C   3
D   4

Nothing really special about it, but it just saved me some work :-)

rayzercork · 20-05-2019 8:41pm

if you have the xfce terminal installed type

xfce4-terminal --drop-down

and it will drop down from the top of your screen. if you create a launcher with that command and stick it into usr/share/applications you can run it from the menu or else assign a keyboard shortcut like F12 to activate it.
i like to run cmus music player inside this terminal because i can hide it out of the way when not needed

lyda · 16-09-2021 12:37pm

If you want to version control your home directory, look at vcsh: https://github.com/RichiH/vcsh

It's also available in most distros. The nice part is that you can put different parts of your home dir in different repos.

Command line tips & tricks

Comments