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bash

screen

screen - screen manager with VT100/ANSI terminal emulation

#Starting Named Session
$ screen -S session_name

#Detach from Linux Screen Session
# Ctrl+a d

$ screen -ls

$ screen -r

Shortcuts

Shortcut Description
Ctrl+a ? Display all shortcut
Ctrl+a c Create a new window (with shell)
Ctrl+a " List all window
Ctrl+a 0 Switch to window 0 (by number )
Ctrl+a A Rename the current window
Ctrl+a S Split current region horizontally into two regions
Ctrl+a Split current region vertically into two regions
Ctrl+a tab Switch the input focus to the next region
Ctrl+a Ctrl+a Toggle between the current and previous region
Ctrl+a Q Close all regions but the current one
Ctrl+a X Close the current region

Files

Find

Search for files in a directory hierarchy

    #change permissions of all folders
    find ./ -type d -exec chmod 0755 {} \; -print
    #change permissions of all files
    find ./ -type f -exec chmod 0644 {} \; -print
    #find all files and print the name
    for file in "$( find ./ -type f )"
    do
        echo "$file"
    done | sort >> ./files.lst
    #find all directories ( in max depth 2 ) and list them
    find . -maxdepth 2 -type d -ls

Manage Files Content

paste

Merge lines of files

    $ ( echo -e "odd\neven" && seq 10) | paste  - - ;
    #odd	even
    #1      2
    #3	    4
    #5	    6
    #7	    8
    #9	    10

Read More

sed

Stream editor for filtering and transforming text

    echo "gray red grayblack Grey" | sed 's/\bgr[ae]y\b/blue/gI' #blue red grayblack blue

    echo "+30 690000000" | sed 's/[[:digit:]]/X/' #+XX XXXXXXXXX

    echo "James Bond" | sed -E 's/(.*) (.*)/My name is \2, \1 \2/' #My name is Bond, James Bond

    #Match all the words that the first half word is same with the other half
    sed -E -n '/^(.*)\1$/p'cd /words

awk

Pattern scanning and processing language

$ awk -F'[[:space:]]' 'BEGIN { printf "Active Hosts\n%-45s %-25s\n", "IP", "Domain";} \
{\
if($0 != "" && !/^#/){\
    printf "%-45s %-25s\n", $1, $NF;\
}\
}\
 END{print "--------------";\
 }'  /etc/hosts

wc

Counts the number of bytes, characters, whitespace-separated words, and newlines in each given FILE, or standard input if none are given or

#Counts the lines of a file 
wc -l <filename>

Manage Files System

chmod

The chmod command is fairly simple in itself, but giving the right permissions to files and directories is a whole different game.

chmod 664 robots.txt
chmod 775 public/images

tar

The Linux tar stands for tape archive. It is used for collecting many files into one archive file.

tar -cvf my-archive.tar /path/to/directory

tar -xvf my-archive.tar -C /home/myfolder/

Transfer Files

scp

Remote secure copy

scp username@remotehost.com:/path/to/foobar.txt /some/local/directory

rsync

rsync -azP $SOURCECORE $DESTINATION

ftp copy

set ftp:ssl-allow no
open $HOST
user $USER $PASS
lcd $SOURCEFOLDER
mirror  --parallel=5 --reverse  --only-newer --verbose --exclude $EXCLUDE1 --exclude $EXCLUDE2 --exclude $EXCLUDE3 --exclude $EXCLUDE4 --exclude $EXCLUDE5 --exclude-glob .*  --exclude-glob *.md   $SOURCEFOLDER $TARGETFOLDER
bye

Network

tcpdump

Capture the TCP layer packets on a production server into a file, then open and view it with Wireshark

ss -s

Check the TCP connection status

Security

ssh-keygen command is used to generate a new SSH key pair.

#Note that in the example above, we used the ED25519 signing algorithm. While ED25519 is considered best practice, you should always do some research on the different available signing algorithms.
ssh-keygen -t ed25519