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Bash (Bourne Again Shell)

Types of Shells

Filesystem Interaction

ls - listing

ls -a - show all (includes hidden files)

cd - change directory

cat - concatenate

pwd - print working directory

Searching for Files

find - find / search

find -name passwords.txt

find -name *.txt

grep - search the contents of files for specific values.

grep '81.144.123.80' access.log

Operators

& - allows you to run commands in the background of your terminal.

&& - allows you to combine multiple commands together in one line of your terminal.

> - redirector - take the output from a command and direct it elsewhere.

>> - same as > but appends the output rather than replacing it.

Filesystem Interaction

touch - create file

mkdir - create a folder

cp - copy a file/folder

mv - move file or folder

rm - remove file or folder; use -R if removing directory

file - determine the type of a file

Permissions

ls -lh - show permissions (-h human readable)

su - switch between users

su user2 - use su to switch to user2

su -l user2 -

Downloading / Transfering Files

wget - allows you to download files via HTTP.

wget https://assets.tryhackme.com/additional/linux-fundamentals/part3/myfile.txt

SCP - allows you to transfer files between two computers using SSH.

scp important.txt [email protected]:/home/ubuntu/transferred.txt - transfer file to the other system

scp [email protected]:/home/ubuntu/documents.txt notes.txt -transfer file from a system to yours.

Processes

ps - view current processes

ps aux - view processes run by other users and those that don't run from a session (i.e. system processes)

top - shows real-time statistics about th eproccesses running on your system instead of a one-time view. Will refresh.

kill - terminate a process along with the PID number

SIGTERM - kill the process, but allow it to do some cleanup
SIGKILL - kill the process, does do any cleanup
SIGSTOP - Stop/suspend a process

Ctrl + Z will background a process.

fg bring process to forground

Cron and Crontabs

crontab -e - edit crontab

          • command_to_execute

| | | | | | | | | +---- Day of the week (0 - 7) [0 and 7 both represent Sunday] | | | +------ Month (1 - 12) | | +-------- Day of the month (1 - 31) | +---------- Hour (0 - 23) +------------ Minute (0 - 59)

example:

30 2 * * 1 /path/to/script.sh

Other Commands

echo $SHELL - see which shell you are using.

cat /etc/shells - see which shells are available to you.