@linux @bash
Useful oneliners
Show dir sizes: du -hs */ | sort -hr | head
Show ssh key ids
for file in $(fd -e pub); do ssh-keygen -lf $file && echo $file; done
for file in $(fd -e pub); do ssh-keygen -l -E md5 -f $file && echo $file; done
ENV via ssh forward
export MYVAR=test
ssh myhost "export MYVAR='$MYVAR' && echo $MYVAR"
# test
A one-liner version incrementer
inc_version() {
awk -F. -vOFS=. '{ $ver++; while(ver++<NF) $ver=0; print $0 }' ver=$1
}
Source: https://gir.st/blog/inc-version.htm
Reset efivars in bootmenu (bootctl)
To remove LoaderEntryDefault-[…] variable it was enough to press d key twice in the boot menu: to set and unset a new value. To remove LoaderConfigTimeout-[…] variable it turned out enough to press Shift+t enough times to set the timeout to 0, plus one more time. Link
Check dns server for dnssec
With dig +dnssec kuketz-blog.de @116.203.32.217 check for flags, needs to have
the ad included, for authenticated answer.
Search in .tar.gz files
rg -a -z 'regex'
List open ports
sudo ss -tulpn
sudo netstat -tulpn | grep LISTEN
sudo lsof -i -P -n | grep LISTEN # process list
sudo lsof -i -n -P | grep TCP # macOS
sudo nmap -sT -O localhost # scan localhost
Find file from iNode Number
find ~/ -inum 123456
Start GUI app in background from commandline
<guiapp> . &!
Run last command as root
sudo !!
Serve current dir tree at :8080
Only in python2
python -m SimpleHTTPServer
Python3:
python3 -m http.server
### Replacing in last command
^sub^to
### Supervise command (run every 2s)
watch “ls -larth”
### Kill program using one port
```bash
sudo fuser -k 8000/tcp
Limit memory usage for following commands
ulimit -Sv 1000 # 1000 KBs = 1 MB
ulimit -Sv unlimited # Remove limit
Rename selected files using a regular expression
rename 's/\.bak$/.txt/' *.bak
Get full path of file
readlink -f file.txt
List contents of tar.gz and extract only one file
tar tf file.tgz
tar xf file.tgz filename }}
List files by size
ls -lS
Nice trace route
mtr google.com
Find files tips
find . -size 20c # By file size (20 bytes)
find . -name "*.gz" -delete # Delete files
find . -exec echo {} \; # One file by line
./file1
./file2
./file3
find . -exec echo {} \+ # All in the same line
./file1 ./file2 ./file3
Print text ad infinitum
yes
yes hello
Who is logged in?
w
Prepend line number
ls | nl
Grep with Perl like syntax (allows chars like \t)
grep -P "\t"
Cat backwards (starting from the end)
tac file
Check permissions of each directory to a file
It is useful to detect permissions errors, for example when configuring a web server.
namei -l /path/to/file.txt
Run command every time a file is modified
while inotifywait -e close_write document.tex
do
make
done
Copy to clipboard
cat file.txt | xclip -selection clipboard
Spell and grammar check in Latex
detex file.tex | diction -bs
You may need to install the following sudo apt-get install diction texlive-extra-utils.
Check resources’ usage of command
/usr/bin/time -v ls
Randomize lines in file
cat file.txt | sort -R
cat file.txt | sort -R | head # Pick a random sambple
Even better (suggested by xearl in Hacker news):
shuf file.txt
Keep program running after leaving SSH session
If the program doesn't need any interaction
nohup ./script.sh &
If you need to enter some input manually and then want to leave
./script.sh
<Type any input you want>
<Ctrl-Z> # send process to sleep
jobs -l # find out the job id
disown -h jobid # disown job
bg # continue running in the background
Of course, you can also use screen or tmux for this purpose.
Run a command for a limited time
timeout 10s ./script.sh
Restart every 30 minutes
while true; do timeout 30m ./script.sh; done
Combine lines from two sorted files
comm file1 file2
Split long file in files with same number of lines
split -l LINES -d file.txt output_prefix
Flush swap partition
If a program eats too much memory, the swap can get filled with the rest of the memory and when you go back to normal, everything is slow. Just restart the swap partition to fix it:
sudo swapoff -a
sudo swapon -a
Fix ext4 file system with problems with its superblock
sudo fsck.ext4 -f -y /dev/sda1
sudo fsck.ext4 -v /dev/sda1
sudo mke2fs -n /dev/sda1
sudo e2fsck -n <first block number of previous list> /dev/sda1
Create empty file of given size
fallocate -l 1G test.img
Manipulate PDFs from the command line
To join, shuffle, select, etc. pdftk is a great tool
pdftk *.pdf cat output all.pdf # Join PDFs together
pdftk A=in.pdf cat A5 output out.pdf # Extract page from PDF
You can also manipulate the content with cpdf
cpdf -draft in.pdf -o out.pdf # Remove images
cpdf -blacktext in.pdf -o out.pdf # Convert all text to black color
Monitor the progress in terms of generated output
Write random data, encode it in base64 and monitor how fast it is being sent to /dev/null
cat /dev/urandom | base64 | pv -lbri2 > /dev/null