shell scripting 101

#!/bin/bash

# give it executable permission
# `chmod +x filename.sh`


echo "Total arguments : $#"
echo "1st Argument = $1"
echo "2nd argument = $2"







# accessing parameters by name
function greeting() {
str="Hello, $name"
str+=" nice to meet you.\nwelcome to: THE SHELL TRAINIG SERIES"
echo $str
}


echo -n "Enter Your Name: "

read name

msg=$(greeting)
echo -e $msg









# accessing parameters by index
sum() {
res=$(($1 + $2))
echo "$res"
}



while [[ true ]]; do

echo -n "Ingresa un numero entre [1..10]: "

read num

# checkeo que es un numero (primero como string; notese los parentesis-rectos)
if [[ ! $num =~ ^-?[0-9]+$ ]] ; then
    echo "No good"
    exit
fi

# lo checkeo como integer (notese los parentesis-curvos)
# if ((num<1)); then
#     echo "$num es menor que 1"
# elif ((num>10)); then
#     echo "$num es mas grande que 10"
# fi

# checkeo 2x1
if ((num<1)) || ((num>10)); then
    echo "$num no es valido"
else
	break # breakea el while
fi
	
done


# pequena aritmetica
(( num = num + 1 ))
echo "its sucessor is $num"

total=$(sum num 123)
echo "and $num + 123 = $total"










echo -n "Enter username: "
read username

echo -n "Enter password: "
read password

if [[ ( $username == "admin" && $password == "secret" ) ]]; then
echo "valid user"
else
echo "invalid user"
fi








echo -n "Enter directory name: "
read newdir
if [ -d "$newdir" ]; then
echo "Directory exist"
else
`mkdir $newdir`
echo "Directory successfully"
fi

# last echo must not contain `-n` flag!!!







# read a file

file='book.txt'
while read line; do
echo $line"asdsss"
done < $file



# delete a file

echo -n "Enter filename to remove: "
read fn

echo "y or n"
rm -rf $fn





# date

Year=`date +%Y`
Month=`date +%m`
Day=`date +%d`
Hour=`date +%H`
Minute=`date +%M`
Second=`date +%S`
echo `date`
echo "Current Date is: $Day-$Month-$Year"
echo "Current Time is: $Hour:$Minute:$Second"