Netcat

chat.sh

#from 
#       https://www.youtube.com/watch?v=LQSMJtckzYI
#  simple chat coomunication between 2 machines with netcat 
#This works with linux, Win
# to install apt-get install netcat-traditional #buntu
#IP 192.168.33.10
nc 192.168.33.10 3137
#IP 192.168.33.11 ; so this machine is listening on the ß0rt 3137 for what 192.168.33.10 is sending, and vicevers
nc -l -p 3137

command_groups.sh

subshell:
  evaluate list of commands in a subshell;environment is distinct from current shell and variable also
  
  form: (list)
  ex:
    unset z; (z=hello; echo $z;); echo $z #the last variable $z is outside the routine, so is empty,ouside the scope of the subshell

group command:
  evaluate list of commands in the current shell,sharing the current shells environment
  
  form: { list; } #spaces is important before and after
  ex:
  unset z; { z=hello; echo $z; }; echo $z #the last variable $z is part of the routine, 
                                          #so is not empty,inside the scope of the group command

usefull grouping:
  
echo b; echo a | sort;  #bad, is not sorted
(echo b; echo a) | sort; #sorted

#show the grouped matriska processes of shells
 echo "$(echo "$(echo "$( ps wwf -s $$)")")"
 




echo "$(echo "$(echo "$(echo "$(ps f  $$)")")")"

conditionals.sh

if list2;then list2;fi
if list1;then list2;else list3;fi  #list2 evaluates only if list1 returns status 0
if list1;then list2;elif list3;then list4;else list5; fi
ex:
  if [ -f license.txt ];then echo 'license';elif [ -f readme.txt ];then echo 'readme';else echo 'none of these'; fi

conditionals_case.sh

case conditionals
case word in
  pattern1)
    list1;;
  pattern2 | pattern3)
    list3;;
esac

ex:
  case one in 
    o)
      echo 'o' #is not matched because is not fully exhausted or complete
    ;;
    o*)
      echo 'o*' #this is matched
    ;;
    *)
      echo 'nope'
    ;;
  esac

dollar_sign.sh

A.----------Parameters

$#    Stores the number of command-line arguments that 
      were passed to the shell program.
$?    Stores the exit value of the last command that was 
      executed.
$0    Stores the the name of the shell program or the shell script.is not a positional parameter
      If started with -c (CMDLINE) option as argument,$0 will be the first argument after CMDLINE
$*    Stores all the arguments that were entered on the
      command line ($1 $2 ...). as a string
"$@"  Stores all the arguments that were entered
      on the command line, individually quoted ("$1" "$2" ...)
#####
$?    Exit status of most recent pipeline
$-    current option flags
$$    PID of the invoked shell              #decimal
$!    PID of most recent background command executed from current shell #decimal
$-    option flags set by shell itself, usually himB
$!    The process ID (PID) of the most recently executed background pipeline (like started with command &)
$_    catck all parameters



ex short:
  $0 :  echo "$0" # -bash or name of the script


ex command line
./command -yes -no /home/username

values of different dollar signs

    $# = 3                         #number
    $* = -yes -no /home/username   #string
    $@ = array: {"-yes", "-no", "/home/username"}   #array
    $0 = ./command, $1 = -yes etc.

looping_conditionals.sh

#Looping and Conditionals in BASH
#
# many infos from
#      https://www.youtube.com/watch?v=uqHjc7hlqd0

#!/bin/bash

#Ex0: iterating words  with select
#like a menu so we can choose what to select from input keyboard
#so, the $choice is the word that corresponds with our number selection($REPLY index)
#if the selection is out of range, $choice is not set
select var1 in one two "three four"
do
  echo "number $REPLY : $choice"     #$REPLY is the index variable of var1 and the value is the selected word
done

#Ex 1; iterating
echo 'Ex1: '
for((i=1;i<=3;i++)); #loops until expr (i<=3) returns a non-zero status(fails)
do                      #each  for  has a do ended with done !
        echo $i; # ";" is optional
done

#Ex 2; just taking a line as a variable
echo 'Ex2: '
for name in  Floki John Levi;
do
        echo ${name};
done

#Ex 3; we take a data and loop thtough it
echo 'Ex3: '
for l in `cat data1.txt`; #not working with '' or "" , gives just data1.txt
do
        echo ${l} | cut -d "," -f 2 #cut is used to filter the data -d = delimiter -f = what columns we want
done

#Ex 4; looping with  < -lt; == -eq ; > -gt ; if elif then else fi
echo 'Ex4: '
cutoff=2
for((i=1;i<=3;i++));
do
        if [ $i -lt $cutoff ];
        then
                echo "$i is less than $cutoff";
        elif [ $i -eq $cutoff ]; # = is for string, -eq for numeric comparision
        then
                echo "$i is same as $cutoff";
        else
                echo "$i is not less than $cutoff"
        fi

done

#Ex 5; just taking a line as a variable
echo 'Ex5: '
for z in Alfa Beta Gamma;
do
        if [ "${z}" = 'Alfa' ];  #note single equal = for comparision of strings;for int use -eq
                then    exit0 #continue  #or use 'continue'  -> for iterating the rest of the code
        else
                echo $z
        fi
done

#interesting reading a list1 and do meanwhile another list2 until list returns non-zero !0 status (fails)
while list1
do
  list2
done
#example: 
while read var1;do echo $var1;done  #reapeats until a non zero exits status 


#until is opposite of while; if a zero status come(succed) fails immediately
#executes list1 ; if fails continue to execute list2 and repeat until list1 returns status 0 (succeds)
until list1
do
  list2
done
#example: 
until read var1;do echo $var1;done  #reapeats until a zero exits status 

pattern_matching.sh

pattern matching

used with [[

* -any
? -single
[character class] -any one of the characters between []
[^...] complement
[x-z] range from x to z
[[:class]] -matches according to POSIX classes:
  alnum alpha ascii blank  cntrl digit graph lower print punct space

remote_shell.sh

#linux to linux, linux to windows etc
#IP 192.168.33.10 Linux
sudo nc -lp 31337 -c /bin/bash
#IP 192.168.33.1 Windows with netcat installed (http://www.securityfocus.com/tools/139 ) 
#and from Powershell or Cmd is connecting to Linux and now you are ready to execute cmd to Linux from WIndows
#like ls, useradd, cat, etc
nc.exe 192.168.33.10 31337

tests.sh

#Tests


[expression] or test expression
    We can evaluate with the test builtin

[[expression]] new way of declaring expressions with bash 3

right side of a comparision is: 1. pattern if NOT quotted 
                                    [[string1==string2]] #so string2 is a pattern
                                2. a string, if quottted
                                    [[string1=="string2"]] #so string2 is a string

[[-n string]]  is non-empty string    #if [[ -n string ]];then echo "hello"; fi
[[-z string]]  is empty string        #if [[ -z string ]];then echo "hello"; fi 
[[string1 == string2]] 1 and 2 are same  #if [[ 'alfa' == 'alfa' ]];then echo "hello"; fi
[[string1 != string2]] 1 and 2 are not same 
[[string1 =~ *]] string1 matches reg express 
[[ -e file.txxt ]] if file exists              #if [[ -e ilsas.txt ]];then echo "hello"; fi
[[ -f file.txxt ]] if is a file              #if [[ -f ilsas.txt ]];then echo "hello"; fi
[[ -d file ]] if is a directory              #if [[ -d ilsas ]];then echo "hello"; fi
[[ -t 0 ]] This test option may be used to check whether the stdin [ -t 0 ] or stdout [ -t 1 ] in a given script is a terminal
            # 0 is for stin input, but we can use 1 ,stdou
            # so if a person is writing something from keyboard the test pass , if is from a script file the input fails
            ex1:
              #the data is coming from us directly( o is for input),so is a terminal
              if [ -t 0 ];then echo 'terminal';else echo 'not terminal';fi
              #the data is coming from a text file ( o is for input),so is not a terminal
              if [ -t 0 ];then echo 'terminal';else echo 'not terminal';fi
            ex2:
              while read f ; do echo $f;if [ -t 0 ];then echo 'not terminal';fi;done < data.txt  #not terminal
              while read f ; do echo $f;if [ -t 0 ];then echo 'terminal';fi;done   #from us, so terminal
              
              

usefull_commands.sh

# vim copy all text
gg"*yG  #gg beginn, "*y start a yank command, G end of file

#read line from text
while read myline
do 
  echo '.......'
  echo "$myline"
done < data.txt

#read from input
while read myline
do 
  echo '.......'
  echo "$myline"
done 

# read the values of two variables from keyboard until Ctrl^c
while read var1 var2
do echo $var2 $var1
done