The Linux Command Line

History Management

Execute the last command with sudo

sudo !!

Recall the last argument of the previous command

!$

Recall all arguments of the previous command

!*

Execute the last command that started with grep

!grep

Quick find-and-replace in the last command

^foo^bar

Global find-and-replace in the last command

!!:gs/foo/bar/

Reverse search your command history

Ctrl+R

Built-in variables

Prints the Process ID (PID) of the current shell

echo $$

Prints the PID of the last command you sent to the background

echo $!

Prints the exit status of the last command.

echo $?

Prints the last argument of the previous command.

echo $_

Prints a random integer between 0 and 32767

echo $RANDOM

Navigation

Go back to the previous directory you were in

cd -

Push the current directory onto a stack

pushd .

Pop a directory from the stack and cd into it

popd

cd into the path of the last argument

cd $_

Networking & Localhost

Pings localhost

ping 0

ping localhost

IPv6

ping ::1

Connect to a local web server on port 8080

curl 0:8080

Process & Job Control

Suspend (pause) the currently running foreground process.

Ctrl+Z

Resume the most recently suspended job in the background

bg

Bring the most recent backgrounded or suspended job to the foreground

fg

List all suspended and backgrounded jobs.

jobs

Kill job number 1

kill %1

base64

Generate MD5 hash

md5sum <file>

Generates a SHA256 hash

sha256sum file.txt

Encoding

Encode File + Redirect Output

base64 file.txt > hash.txt

Encode String + Redirect Output

echo "your_string_here" | base64 > encoded_file.txt

• In Base64 encoding, by default, some implementations add line breaks every 76 characters (following the RFC 2045 standard).

Encode File Without line break

base64 -w 0 <file>

Encode String without line breaks

echo -n "your_string_here" | base64 -w 0

---

Safe URL encoding

base64 -w 0 <file> | tr '+/' '-_' > url_safe_encoded.txt

Decoding

Decode String + Output to a file

echo <string> | base64 -d > <file>

Decode File + Output to a file

base64 -d -i <file> > <decoded_file>

Decode File without line breaks

base64 -d -w 0 file.txt > decoded_output.bin

Chroot

Decrypt the system

Decrypt partition

sudo cryptsetup luksOpen /dev/sda3 cryptdisk

Mounts the decrypted device

sudo mount /dev/mapper/cryptdisk /mnt

Mounts the boot partion

sudo mount /dev/sda1 /mnt/boot

chroot into a mounted partition

sudo arch-chroot /mnt

Connect using WPA

Shows connection status

wpa_cli status

Creates the passphrase

sudo wpa_passphrase "MyWiFi" "mypassword123" | sudo tee /etc/wpa_supplicant/wpa_supplicant.conf

Connect using passphrase

sudo wpa_supplicant -B -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf

Boot/UEFI Management

Displays the current boot entries in the UEFI firmware

efibootmgr

deletes the boot entry "0"

sudo efibootmgr --delete-bootnum --bootnum 0