Operators
Arithmetic operators
#!/bin/bash

expr 1 + 3
expr 2 - 1
expr 2 \* 4 # escape wildcard character *
expr 4 / 2
expr 10 % 3

let z=5**3; echo $z # exponentiation

a=`expr 1 + 3`; echo $a
a=$(expr 1 + 3); echo $a
a=$(( 1 + 3 )); echo $a

let "a += 10"; echo $a # +=, -=, *=, /=, %=
(( ++a )); echo $a # ++, --
Logical operators
  • !, not
  • &&, and
  • ||, or
    • #!/bin/bash

# <, <=, >, >=
echo `expr 1 \< 3` # 1, true
echo `expr 0 \> 2` # 0, false
echo `expr 5 \!= 5` # 0
echo `expr 5 == 5` # ==
  • -eq, -ne, -gt, -lt, -ge, -le
    • #!/bin/bash

a=10
b=100

if [ $a != $b ]
then
	echo "Not equal"
fi

if [ $a -lt $b ]
then
	echo "Less than"
fi
    Boolean operators
  • !, not
  • -a, and
  • -o, or
    • #!/bin/bash

a=10
b=100

if [ $(($a % 2)) == 0 -a $a -gt 5 ]
then
	echo "Even and greater than five"
fi
    Bitwise operators
    #!/bin/bash

a=1
((a <<= 1)); echo $a # 2
a=$(( a << 1 )); echo $a # 4
    Quotes
  • ", anything enclose in double quotes removed meaning of that characters (except \ and $)
  • ', enclosed in single quotes remains unchanged
  • `, to execute command
    • #!/bin/bash

echo "Name: $USER" # Name: lchen
echo 'Name: $USER' # Name: $USER
echo `pwd` # /home/lchen
echo "Today is `date`"
    Reference