More information: http://linuxconfig.org/Bash_scripting_Tutorial

----------------------------------------------------------------

--Basic Variable--

#!/bin/bash
STRING="Hello World"
echo $STRING

 

--Read in Variable--

#!/bin/bash
echo -e "Input: \c "
read  word
echo "Output: $word"
echo -e "Enter two words? "
read word1 word2
echo "Output: \"$word1\" \"$word2\""
echo -e "How do you feel about bash scripting? "
# read command now stores a reply into the default build-in variable $REPLY
read
echo "You said $REPLY"
echo -e "What are your favorite colours ? "
# -a makes read command to read into an array
read -a colours
echo "My favorite colours are also ${colours[0]}, ${colours[1]} and ${colours[2]}:-)"

-- Variable from a command--

var=$(command-name-here)
var=$(command-name-here arg1)
var=$(/path/to/command)
var=$(/path/to/command arg1 arg2)

--Command in Echo--

echo "Text $(command-name)"
echo "Here are the users $(w)"

--Arrays--

#!/bin/bash
#Declare array with 4 elements
ARRAY=( 'Debian Linux' 'Redhat Linux' Ubuntu Linux )
# get number of elements in the array
ELEMENTS=${#ARRAY[@]}
# echo each element in array
# for loop
for (( i=0;i<$ELEMENTS;i++)); do
echo ${ARRAY[${i}]}
done

 

--Read in a File--

#!/bin/bash
#Declare array
declare -a ARRAY
# Link filedescriptor 10 with stdin
exec 10<&0
# stdin replaced with a file supplied as a first argument
exec < $1
let count=0
while read LINE; do
ARRAY[$count]=$LINE
((count++))
done
echo Number of elements: ${#ARRAY[@]}
# echo array's content
echo ${ARRAY[@]}
# restore stdin from filedescriptor 10
# and close filedescriptor 10
exec 0<&10 10<&-

 

--IF / Else--

#!/bin/bash
directory="./BashScripting"
# bash check if directory exists
if [ -d $directory ]; then
echo "Directory exists"
else
echo "Directory does not exists"
fi

 

--Arithmentic Comparison--

-lt
-gt
-le
-ge
-eq
-ne
< 
> 
<=
>=
==
 

               
               
               
               
               
               

 

#!/bin/bash
# declare integers
NUM1=2
NUM2=2
if [ $NUM1 -eq $NUM2 ]; then
echo "Both Values are equal"
else
echo "Values are NOT equal"
fi

 

--String Comparison--

=

!=

< 

> 

-n s1

-z s1

Equal

Not equal

Less then

Greater then

String s1 is not empty

String s1 is empty

 
#!/bin/bash
#Declare string S1
S1="Bash"
#Declare string S2
S2="Scripting"
if [ $S1 = $S2 ]; then
echo "Both Strings are equal"
else
echo "Strings are NOT equal"
fi

--FOR Loop--

#!/bin/bash
# bash for loop
for f in $( ls /var/ ); do
echo $f
done
 
Running for loop from bash shell command line:
$ for f in $( ls /var/ ); do echo $f; done

-----OTHER WAYS to USE FOR LOOP-----

for VARIABLE in 1 2 3 4 5 .. N
do
	command1
	command2
	commandN
done
------------------------------------
for VARIABLE in file1 file2 file3
do
	command1 on $VARIABLE
	command2
	commandN
done
------------------------------------
for OUTPUT in $(Linux-Or-Unix-Command-Here)
do
	command1 on $OUTPUT
	command2 on $OUTPUT
	commandN
done
------------------------------------
for i in 1 2 3 4 5
do
   echo "Welcome $i times"
done
------------------------------------
for i in {1..5}
do
   echo "Welcome $i times"
done
------------------------------------
for i in {0..10..2}
  do
     echo "Welcome $i times"
 done


for (( EXP1; EXP2; EXP3 ))
do
	command1
	command2
	command3
done

------------------------------------
for (( c=1; c<=5; c++ ))
do
   echo "Welcome $c times"
done
 
------------------------------------
Infinite for loop can be created with empty expressions, such as:

#!/bin/bash
for (( ; ; ))
do
   echo "infinite loops [ hit CTRL+C to stop]"
done
------------------------------------
You can do early exit with break statement inside the for loop. You can exit from within a FOR, WHILE or UNTIL loop using break. General break statement inside the for loop:

for I in 1 2 3 4 5
do
  statements1      #Executed for all values of ''I'', up to a disaster-condition if any.
  statements2
  if (disaster-condition)
  then
	break       	   #Abandon the loop.
  fi
  statements3          #While good and, no disaster-condition.
done
------------------------------------
#!/bin/bash
for file in /etc/*
do
	if [ "${file}" == "/etc/resolv.conf" ]
	then
		countNameservers=$(grep -c nameserver /etc/resolv.conf)
		echo "Total  ${countNameservers} nameservers defined in ${file}"
		break
	fi
done
------------------------------------
for I in 1 2 3 4 5
do
  statements1      #Executed for all values of ''I'', up to a disaster-condition if any.
  statements2
  if (condition)
  then
	continue   #Go to next iteration of I in the loop and skip statements3
  fi
  statements3
done


--While Loop--

#!/bin/bash
COUNT=6
# bash while loop
while [ $COUNT -gt 0 ]; do
echo Value of count is: $COUNT
let COUNT=COUNT-1
done

--Until Loop--

#!/bin/bash
COUNT=0
# bash until loop
until [ $COUNT -gt 5 ]; do
echo Value of count is: $COUNT
let COUNT=COUNT+1
done

--Functions --

!/bin/bash
# BASH FUNCTIONS CAN BE DECLARED IN ANY ORDER
function function_B {
echo Function B.
}
function function_A {
echo $1
}
function function_D {
echo Function D.
}
function function_C {
echo $1
}
# FUNCTION CALLS
# Pass parameter to function A
function_A "Function A."
function_B
# Pass parameter to function C
function_C "Function C."
function_D

--Select--

#!/bin/bash
PS3='Choose one word: '
# bash select
select word in "linux" "bash" "scripting" "tutorial"
do
echo "The word you have selected is: $word"
# Break, otherwise endless loop
break 
done
exit 0

--CASE Condition--

#!/bin/bash
echo "What is your preferred programming / scripting language"
echo "1) bash"
echo "2) perl"
echo "3) phyton"
echo "4) c++"
echo "5) I do not know !"
read case;
#simple case bash structure
# note in this case $case is variable and does not have to
# be named case this is just an example
case $case in
echo "You selected bash";;
echo "You selected perl";;
echo "You selected phyton";;
echo "You selected c++";;
exit
esac