30 interesting commands for the Linux shell
14 Sep, 2017
This article got pretty big on Hacker News, check the discussion there for some interesting comments.
These are 30 interesting commands and tips for the Linux shell that I have collected over the years.
1. Supervise command (run every 2s)
watch "ls -larth"
2. Kill program using one port
sudo fuser -k 8000/tcp
3. Limit memory usage for following commands
ulimit -Sv 1000 # 1000 KBs = 1 MB
ulimit -Sv unlimited # Remove limit
4. Rename selected files using a regular expression
rename 's/\.bak$/.txt/' *.bak
5. Get full path of file
readlink -f file.txt
6. List contents of tar.gz and extract only one file
tar tf file.tgz
tar xf file.tgz static
7. List files by size
ls -lS
8. Nice trace route
mtr google.com
9. 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
10. Print text ad infinitum
yes
yes hello
11. Who is logged in?
w
12. Prepend line number
ls | nl
13. Grep with Perl like syntax (allows chars like \t)
grep -P "\t"
14. Cat backwards (starting from the end)
tac file
15. 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
16. Run command every time a file is modified
while inotifywait -e close_write document.tex
do
make
done
17. Copy to clipboard
cat file.txt | xclip -selection clipboard
18. 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.
19. Check resources' usage of command
/usr/bin/time -v ls
20. 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
21. 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.
22. Run a command for a limited time
timeout 10s ./script.sh
# Restart every 30 minutes
while true; do timeout 30m ./script.sh; done
23. Combine lines from two sorted files
comm file1 file2
Prints these three columns:
- Lines unique to
file1. - Lines unique to
file2. - Lines both in
file1andfile2.
With options -1, -2, -3, you can remove each of these columns.
24. Split long file in files with same number of lines
split -l LINES -d file.txt output_prefix
25. 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
26. 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
27. Create empty file of given size
fallocate -l 1G test.img
28. 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
29. 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
# pv options:
# -l, lines
# -b, total counter
# -r, show rate
# -i2, refresh every 2 seconds
30. Find packages that have a given file in Ubuntu
apt-file update
apt-file search dir/file.h