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Cake day: October 19th, 2023
  • ClusterBomb@lemmy.blahaj.zonetoLinux@lemmy.ml•30 interesting commands for the Linux shellEnglish
    46·
    7 months ago
    1. Supervise command (run every 2s)
    watch "ls -larth"
    1. Kill program using one port
    sudo fuser -k 8000/tcp
    1. Limit memory usage for following commands
    ulimit -Sv 1000       # 1000 KBs = 1 MB
ulimit -Sv unlimited  # Remove limit
    1. Rename selected files using a regular expression
    rename 's/\.bak$/.txt/' *.bak
    1. Get full path of file
    readlink -f file.txt
    1. List contents of tar.gz and extract only one file
    tar tf file.tgz
tar xf file.tgz static
    1. List files by size
    ls -lS
    1. Nice trace route
    mtr google.com
    1. 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
    1. Print text ad infinitum
    yes
yes hello
    1. Who is logged in?
    w
    1. Prepend line number
    ls | nl
    1. Grep with Perl like syntax (allows chars like \t)
    grep -P "\t"
    1. Cat backwards (starting from the end)
    tac file
    1. 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
    1. Run command every time a file is modified
    while inotifywait -e close_write document.tex
do
    make
done
    1. Copy to clipboard
    cat file.txt | xclip -selection clipboard
    1. 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.

    1. Check resources’ usage of command
    /usr/bin/time -v ls
    1. 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
    1. 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.

    1. Run a command for a limited time
    timeout 10s ./script.sh

    # Restart every 30 minutes

    while true; do timeout 30m ./script.sh; done
    1. Combine lines from two sorted files
    comm file1 file2

    Prints these three columns:

    Lines unique to file1.
Lines unique to file2.
Lines both in file1 and file2.

    With options -1, -2, -3, you can remove each of these columns.

    1. Split long file in files with same number of lines
    split -l LINES -d file.txt output_prefix
    1. 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
    1. 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
    1. Create empty file of given size
    fallocate -l 1G test.img
    1. 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
    1. 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
    1. Find packages that have a given file in Ubuntu
    apt-file update
apt-file search dir/file.h