Bash

Frequently used bash snippets

Check memory from bash

free -mh

Check access through ssh

last | head

Check open ports nmap

while :; 
do nmap <addres> -p443,9200,80,22 -Pn --max-rtt-timeout 60ms  ;
sleep 1 ; done

Check open ports lsof

sudo lsof -i -P -n #or
sudo lsof -i -P -n | grep LISTEN #or
lsof -i :8000 # by port

Openning port in ubuntu

sudo ufw allow [PORT]

If statements

if [ -z STRING]
then
fi

If with multiple conditions and checking lenght == 0

if [ -z $VAR1 ] || [ -z $VAR2]; then
# code
fi

Uninstall packages

sudo apt remove pkg

Kill processes

kill -9 PID

Search keywords in files within a directory

grep -Hrn 'search term' path/to/files

Remove character in-place

sed -i 's/past/future/g' file.txt

Remove a specific line from file

sed -i 'Ld' file.txt
# L is the linenumber to delete

Add character to the beginning of the file

sed -i '1s/^/future/' file.txt

Remove first line from file

tail -n +2 FILE

Create sudo user

adduser username

usermod -aG sudo username

List omitting directory

ls -1R -I [omit_dir]

Collect http urls from several csv into a single one

cat urls.html | grep -Eo "(http|https)://[a-zA-Z0-9./?=_%:-]*" | sort -u

cURL requests

curl --header "Content-Type: application/json" \
  --request POST \
  --data '{"username":"xyz","password":"xyz"}' \
  http://localhost:3000/api/login

Delete history entry

history -d <line_number>

tmux

Create a new session

tmux new -s sessionName
## Detached mode:
#tmux new -d -s sessionName

List sessions

tmux ls

Attach a session

tmux a -t sessionName

Detach a session

C-a + d

Send a command to a detached session

tmux send-keys -t sessionName.0 "echo 'Hello world'" ENTER

Split panes for detached sessions

tmux splitw -h -p 50 -t sessionName:1.0
# -p percentage of the display for the created pane
# -h or -v # horizontal/vertical splitting
## if we need to do it again we may need to select the pane we want to split first
tmux select-pane -t sessionName:1.0
tmux splitw -h -p 50 -t sessionName:1.0

Compress file

tar -zcvf outputFileName folderToCompress

unzip file

sudo apt install unzip #(ubuntu)
unzip target_file.zip

Text processing

Get specific line from file

sed -n LINEp target_file

awk > sed for big files

Substitute char in big file

aws '{gsub(/old/,"NEW"); print}' in_file > out_file

Might require LC_ALL=C at the beginning depending on in_file encoding

Get content between START and END pattern

sed -n '/^CREATE TABLE/,/GO/p'

Generate a password or key

openssl rand -base64 32

Generate base64 encoded for text

echo 'to_encode' | base64

References

• https://dev.to/thiht/shell-scripts-matter

• Awesome shell