Cheat Sheet :: Linux Shell Tricks

To find the corresponding hex code

echo -n "&" | hexdump -C

How to redirect standard error in bash

nixCraft Article

Command Description/Purpose
command 2>filename Redirect stderr to filename
command >output 2>filename Redirect stderr to file named filename and stdout to file named output
command &> filename Redirect stderr and stdout to filename
command 2>&- Just suppress error messages. No file created. No error message displayed on screen
command 2>/dev/null Just suppress error messages.
command 2>&1 Redirect error messages to standard output. Useful in shell script when you need to forcefully display error messages on screen

Removing blank spaces and special chars

Note that we cannot just type the accent ^, instead we must use CTRL+V and then type CTRL+M.

Using Vim Editor

  • If you want to remove blank lines (using vi): :g/^$/d

  • For commented lines (using vi): :g/^#/d

  • For lines where windows editor put ^M and you want to remove (using vi). :%s/^V^M//g

  • The final command will look like this: :%s/^M//g

Using sed

sed -e "s/^M//" >

Using Dos2Unix

dos2unix input
dos2unix -b input

Using tr

To delete a CRLF:

tr -d '\r' < input > output

Using egrep

egrep -v "^#|^$" squid.original > squid.conf

Using grep

grep -v ^["#"] squid.original > squid.conf

Interactive shell

Using rlwrap

rlwrap nc -nlv 443
rlwrap ./

Using python

  • Once you have a shell on the victim:
python -c 'import pty;pty.spawn("/bin/bash")'


/usr/bin/python3 -c 'import pty;pty.spawn("/bin/bash")'
  • Press CTRL+Z
  • On attacker’s machine:
stty raw -echo
  • Now press fg to get the shell back

Backup of files permissions

  • To create the permission file
getfacl -Rp /home/psylinux/Desktop > /home/psylinux/permissoes_desktop.txt
  • To restore the permissions from file
setfacl --restore=/home/psylinux/permissoes_desktop.txt -R

  • Installation
apt install stow
  • Managing soft links
stow -v -t Target Folder1 Folder2 Folder3
stow -v -D -t Target Folder1 Folder2 Folder3
stow -v -R -t Target Folder1 Folder2 Folder3 Folder4
stow -v -R -t Target Folder1 --ignore='SubFolder1' --ignore='SubFolder2'
stow -v -R -t Target Folder1 --ignore='(?:\..*|[^+]*\+[^+]*)'