Bash Scripting Zero to Hero Examples

debugging.sh

#debugging shellscripts -x would show the scrips line by line and output followed by
#!/bin/bash -x
TEST_VAR="test"
echo "$TEST_VAR"
#custom
#set -x / start debugginh 
#set +x / stop
#-ex exit on stop
#-v prints shell before substitution are applied
#-vx 
#DEBUG="echo"
#$DEBUG ls

decisions_case.sh

#!/bin/bash
#case statement example
read -p "Enter y or n:" ANSWER
case "$ANSWER" in
    [yY]|[yY][eE][sS])
        echo "You answered yes."
        ;;
    [nN]|[nN][oO])
        echo "You answered no."
        ;;
   *)
        echo "Invalid answer."
        ;;
esac

decisions_if.sh

#!/bin/bash
#decisions
HOST_NAME="windows"
#simple if
if [ $HOST_NAME = "ubuntu" ]; then
        echo "Ubuntu for humans"
fi
#if else
if [ $HOST_NAME = "ubuntu" ]; then
        echo "Ubuntu for humans"
else
        echo "Windows for !humans"
fi
#if elif else
if [ $HOST_NAME = "ubuntu" ]; then
        echo "Ubuntu for humans"
elif [ $HOST_NAME = "windows" ]; then
        echo "We !Love Windows"
else
        echo "Windows for !humans"
fi

define_variables.sh

#!/bin/bash

#declare variable
SERVER_NAME="nginx"
echo $SERVER_NAME
echo "We are running on $SERVER_NAME"
echo "We are ${SERVER_NAME}er";

#command output to variable
SERVER_NAME=$(hostname)
echo "We are running on $SERVER_NAME"

file_operations.sh

#!/bin/bash
#file operators
FILE="basic.sh"
if [ -e $FILE ]; then
        echo "File Exists"
else
        echo "No File Found"
fi

#-d,e,r,w,x
#string operations
#arithmetic operations are allowed
#arg1 -eq arg2 - equalto
#arg1 -ne arg2 - !equalto
#arg1 -lt arg2 - less than
#arg1 -le arg2 - less than equalto
#arg1 -gt arg2 - greater than
#arg1 -ge arg2 - greater than equalto

logging_example.sh

#syslog
  
#logger -p user.info "$MESSAGE"
#logger -i -t randomly -p user.info "$MESSAGE"
#while loop
while [ "$CORRECT" != "y" ]
do
        read -p "Whats your name ? " NAME
        read -p "Is your Name: $NAME - correct ?" CORRECT
done
#read file line by line
LINE_NUM=1
while read LINE
do
  echo "${LINE_NUM}: ${LINE}"
  ((LINE_NUM++))
done < /etc/fstab

loops.sh

#!/bin/bash
#loops
COLORS="red green blue"
for COLOR in $COLORS
do

wildcard_examples.sh

#!/bin/bash
#wildcards *.txt match zero or more characters
#?.txt match exactly one character
ls *\? #file end with ?
ls ? #file 1 character
ls -l *.txt
ls c[aeiou]t #character class
#can use this with mv cp rm
#copy .html files to another folder - wildcards
cd /var/www
for FILE in *.html
do
        echo "Copying $FILE"
        cp $FILE /var/www-backup
done