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20 one-line Linux commands to add to your toolbox

Every Linux user has a favorite single-line command. Here are the 20 Linux commands we can't live without.
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Command line output in the terminal

Image by joffi from Pixabay

Many Linux users have experienced a lasting sense of accomplishment after composing a particularly clever command that achieves multiple actions in just one line or that manages to do in one line what usually takes 10 clicks and as many windows in a graphical user interface (GUI). Aside from being the stuff of legend, one-liners are great examples of why the terminal is considered to be such a powerful tool.

By the end of this article, you will have:

  • A list of 20 commands that will make your tasks easier when working on Linux
  • An understanding of the possibilities of combining simple commands to create more powerful commands
  • More fun than you might expect running these commands

Without any specific order of importance, these are our top 20 one-liners for the Linux terminal. Although we've divided some of the longer commands with the \ symbol for easier readability, you can enter them all on a single line in your terminal because, after all, they are one-liners.

1. Apply a command on files with different names

The shell {} operator is great for this. Here's an example with three directories enclosed in {}:

$ mkdir -p -v /home/josevnz/tmp/{dir1,anotherdir,similardir}

2. Edit a file in place

Do you want to replace a string on one or more files without using an editor? Sure, sed to the rescue:

$ sed -i 's#ORIGINAL_VALLUE#NEW_VALUE#g' myfile1 myfile2

But wait, Perl lovers will tell you they can do the same:

$ perl -p -i -e 's#ORIGINAL#NEW_VALUE#' myfile1 myfile2

3. Share a file quickly using a web server

Raise your hand if you haven't used this at least once to share a directory quickly:

$ cd $mydir && python3 -m http.server 8888

4. Find failures with journalctl

Sometimes things break. You can find the most recent errors using a combination of journalctl, along with the classic tools sort and uniq:

$ journalctl --no-pager --since today \
--grep 'fail|error|fatal' --output json|jq '._EXE' | \
sort | uniq -c | sort --numeric --reverse --key 1

898172 "/usr/bin/dockerd"
    752 "/usr/local/sbin/node_exporter"
     30 "/usr/bin/gnome-shell"
     26 "/usr/bin/cat"
     22 "/usr/libexec/gsd-media-keys"
[...]

In this case, it seems that the Docker daemon is unhappy.

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5. Make a backup via encrypted file transfer

Use ssh and tar to make secure backups. They go together like peanut butter and jelly:

$ tar --create --directory /home/josevnz/tmp/ --file - *| \
ssh raspberrypi "tar --directory /home/josevnz \
--verbose --list --file -"

You can add flavor to the backup job with compression and encryption—just like adding ingredients to your sandwich.

6. Write instantaneous files

This is a great trick when you need to write multiline documents:

$ cat<<DOC>/my/new/file
Line1
Line2
A $VARIABLE
DOC

You can also just cat > file, and when you are done editing, just input the EOF character (Ctrl+D):

[josevnz@dmaf5 temp]$ cat > testfile
This is a test
multiple lines
and here we go
[josevnz@dmaf5 temp]$ 

7. Search for a file, and include some extensions and exclude others

This example uses the grep way to search for specific files. It's pretty fast and easy to remember:

$ grep -R 'import' --include='*.java' --color MySourceCodeDir

Or you can try the find way (use xargs to handle a large number of matches properly):

$ find MySourceCodeDir/ -name '*.java' -type f -print| xargs \
grep --color 'import

Why find, you may ask? You can combine find with -exec to execute actions on your files first and then pass the results to the filter. The processing possibilities are endless here.

8. Monitor memory without top or htop

This one is almost cheating. It repeats a command, such as free, every five seconds and highlights the differences:

$ watch -n 5 -d '/bin/free -m'

9. Display disk partition sizes

Use lsbk (list block) and jq (to manipulate a JSON on the command line) to display partition information:

$ lsblk --json | jq -c '.blockdevices[]|[.name,.size]'
["loop0","55.5M"]
["loop1","156M"]
["loop2","32.3M"]
["zram0","4G"]
["nvme0n1","476.9G"]

10. Quickly display a file type

The What is function is called with wi. It quickly tells you a file's type.

To check a single file:

$ function wi { test -n "$1" && stat --printf "%F\n" "$1"; }

To check multiple files:

$ function wi { test "$#" -gt 0 && stat --printf "%n: %F\n" "$@"; }

NOTE: Functions are superior and can do the same work as an alias.

11. Display the size of an installed RPM

If you have an RPM-based system, sooner or later, you will format your queries. Here's an example:

$ rpm --queryformat='%12{SIZE} %{NAME}\n' \
-q java-11-openjdk-headless

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12. Display the total size of a group of files

In this case, the find command acts as a filter, displays the size of each file in bytes, and finally, shows the total size:

$ t=0; for n in $(find ~/Documents -type f -name '*.py' -print | xargs \
stat --printf "%s "); do ((t+=n)); done; echo $t

Or, if you want a function (better), try this approach:

$ function size { t=0; test -d "$1" && for n in $(find $1 \
-type f -name '*.py' -print| \
xargs stat --printf "%s "); do ((t+=n)); done; echo $t; }

size $mydir

13. Update all Git repositories on a directory

You already know how useful Git is. Here's a trick to be more efficient with your updates:

$ for i in */.git; do cd $(dirname $i); git pull; cd ..; done

14. Expose a web directory using containers

Containers are critical today. This one-liner exposes a directory via Podman:

$ podman run --rm -v .:/usr/share/nginx/html:ro,Z \
-p 30080:80 -d nginx

15. Check the weather

Use this function to find out whether you need a jacket today:

weather() { curl -s --connect-timeout 3 -m 5 http://wttr.in/$1; }

16. Display the top 10 IP addresses hitting a webserver

Here's a task web admins may use frequently with Nginx (it may also work with Apache) to grab the top 10 internet protocol addresses hitting a webserver from the access log:

$ cat /var/log/nginx/access.log | cut -f 1 -d ' ' | sort | \
uniq -c | sort -hr | head -n 10

17. Round floats in Bash with Python's help

You can do pretty cool stuff with Python, but this example just rounds numbers:

$ echo "22.67892" | python3 -c "print(f'{round(float(input()))}')"
23

18. Run a mini calculator

This function defines a quick calculator on the command line with variable precision (the default is 2). It uses bc. Create the function like this:

$ function qqbc() { echo "scale=${2:-2}; $1" | bc -l

Next, perform a quick calculation:

$ qqbc "2/3"
.66

In case you need additional precision, just define a second parameter:

$ qqbc "2/3" 4
.6666

This tool is called qqbc because it's an improvement on the old function qbc.

19. Convert a CSV to JSON

This trick is a modification of this popular recipe to convert CSV files to the JSON format:

$ python3 -c \
"import csv,json,sys;print(json.dumps(list(csv.reader(open(sys.argv[1])))))" \
covid19-vaccinations-town-age-grp.csv

20. Install and run commands with Docker

If you have Docker installed and you want to run a command without installing a bunch of dependencies on your system (while doing a quick run), this may be all you need:

$ docker run --rm --interactive curlimages/curl curl \
--verbose --location --fail --silent --output - \
https://example.com

The command runs the latest version of curl from a container, and later removes it. Notice that the command ends with a dash (-), which tells curl to output to your terminal. The possibilities are endless here.

Wrap up

The ability to build powerful combinations of simple commands is one of the reasons Unix and Linux are so popular.

Fortunately. it is not difficult to learn these one-liners. Focus on remembering what a simple command does, and then think about how you can mix many simple commands to make a powerful recipe.

Always check the man page or use the info command to figure out what else the tool can do. You may be surprised to learn that one tool can do everything without combining it with another utility.

There are many sites on the internet with plenty of one-line examples. We hope these examples will lead you to write better one-liners of your own.

Check out these related articles on Enable Sysadmin

Topics:   Linux   Programming   Command line utilities  
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Jose Vicente Nunez

Proud dad and husband, software developer and sysadmin. Recreational runner and geek. More about me

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Anthony Critelli

Anthony Critelli is a Linux systems engineer with interests in automation, containerization, tracing, and performance. He started his professional career as a network engineer and eventually made the switch to the Linux systems side of IT. He holds a B.S. and an M.S. More about me

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Ricardo Gerardi

Ricardo Gerardi is a Senior Consultant at Red Hat Canada where he specializes in IT automation with Ansible and OpenShift.  More about me

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Roberto Nozaki

Roberto Nozaki [RHCSA/RHCE]  is a Senior Consultant at Red Hat Canada where he specializes in IT automation with Ansible. More about me

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