bash if examples

bash_if_&_loop.sh

#!/bin/bash

Reading
####################################

read -e -p "Enter value: " value # saves read input to var, $value
read -n 1 -p "Type a character > " #reads one character saves to default read var $REPLY 

Cheking
####################################
#String cheking

#Checks if empty
[[ -n "$filesystem" ]] #return 1 if empty

#Check if no argument entered
if [ $# -eq 0 ] 
    then 
    echo "Usage: randomExample word" 
    exit 1 
fi 


#find only ip adresses
grep -Eoa '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'  /var/log/auth.log

ip a | grep inet | awk '{ print $2 }'


Letter comparison
####################################

read character
if [[ $character == 'Y' || $character == 'y' ]]
then 
    echo "YES"
else 
    echo "NO"
fi
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read x
if [ "$x" == "Y" ] || [ "$x" == "y" ]; then
    echo "YES"
elif [ "$x" == "N" ] || [ "$x" == "n" ]; then
    echo "NO"
fi

#function for input
function ask() {
echo "[y/n]"
read x
if [ "$x" == "Y" ] || [ "$x" == "y" ]; then
        echo "Executing..."
elif [ "$x" == "N" ] || [ "$x" == "n" ]; then
    echo "Skipping..."
        (exit 1)
    fi

}
#better version with case
function ask() {
  echo "[y/n]"
  read x
  case "$x" in
          y|Y)
              echo "Komanda vykdoma..."
              echo
              ;;

          *)
              echo "Komanda atsaukta."
              exit 1
  esac
}

ask && ls #exaple
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if [ "$BASH" ] && [ "$BASH" != "/bin/sh" ]; then echo "Not sh"; fi


loops
####################################
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for str in $(ls); do echo $str; done
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ls | while read; do echo $REPLY; done
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for NUMBER in 1 2 3 4 5; do echo $NUMBER; done
for i in {1..10}; do printf '%d\n' "$i"; done
for FILE in $(ls); do echo $FILE; done

i=1; while [ $i -lt 10 ]; do echo -n $i; let i=$i+1; done 
i=1; until [ $i -gt 10 ]; do printf '%d\n' "$i"; i=$((i+1)); done
------------------------------------

arrays
####################################
programs=(httpd mysql-server php php-mysql wget unzip)

#array itteration example
for i in "${programs[@]}"
do
        rpm -q $i > /dev/null 2>&1
        if [ $? -eq 1 ]; then
                echo "Error: $i not found. Install? [y/n]"
                read x
        if [ "$x" == "Y" ] || [ "$x" == "y" ]; then
                echo "installing $1"
                yum install $i -y
        elif [ "$x" == "N" ] || [ "$x" == "n" ]; then
                echo "Skipping $i install"
        fi
        fi
done