Команда let в Linux с примерами

Команда let используется для вычисления арифметических выражений переменных оболочки.

Синтаксис:

 пусть [выражение]

Options:

• Basic arithmetic operators : The addition(+), subraction(-), multiplication(*), division(/) and modulus(%) operators can be used in the expression with the let command.

  Example:

  let "myvar =2" "myvar1=1" "myvar2=myvar1+myvar"; echo $myvar2
  let "myvar =2" "myvar1=1" "myvar2=myvar1-myvar"; echo $myvar2
  let "myvar =2" "myvar1=1" "myvar2=myvar1*myvar"; echo $myvar2
  let "myvar =2" "myvar1=1" "myvar2=myvar1/myvar"; echo $myvar2
  let "myvar =2" "myvar1=1" "myvar2=myvar1%myvar"; echo $myvar2
  

  

• Post-increment(var++) / Post-decrement(var–) operator : This operator is used to interpret the integer value then increase/decrease the integer variable by 1.

  Example:

  let "myvar=2" "myvar2=myvar++" ; echo $myvar $myvar2

  

  In the above example, myvar2 gets the value of myvar2 before the increment occurs.

• Pre-increment(++var) / Pre-decrement(–var) operator : This operator increases/decreases the integer value by 1 and then interpret the integer variable.

  Example:

  let "myvar=10" "myvar2=--myvar"; echo $myvar $myvar2

  

  In the above example, the change in value occurs first then the value gets stored in myvar2.

• Unary plus(+exp) / Unary minus(-exp) : This operator is used to multiply a given expression by 1 or -1.

  Example:

  

  In the above example, The value of myvar changes from positive to negative with unary minus operator.

• Bit-wise negation(~) : This operator is used to negate every bit of the integer value i.e., turns 0 to 1 and 1 to 0.

  Example:

  let "myvar=0" "myvar= ~myvar"; echo $myvar

  

  In the above example, The value myvar is ‘0000…00’ in binary while the negation is ‘1111…11’ which is the 2’s complement value of -1.

• Exponent(**) operator : This operator is used to raise one quantity to the power of another.

  Example:

  let "myvar= 5 ** 2" ; echo $myvar

  

• Bitwise shift left / Bitwise shift right : This operator is used to shift the order of the bits either to the left or right.

  Example:

  let "myvar = 5 << 2"; echo $myvar

  

• Bitwise AND operator : This operator does a bitwise comparison between two bits and returns 1 if both are 1 else returns 0.

  Example:

  let "myvar=5" "myvar2=4" "myvar3 = myvar & myvar2" ; echo $myvar3

  

• Bitwise OR operator : This operator does a bitwise comparison between two bits and returns 1 if atleast one the bits is 1, else returns 0.

  Example:

  let "myvar=7" "myvar2=4" "myvar3= myvar | myvar2" ; echo $myvar3

  

• Bitwise XOR operator : This operator does a bitwise comparison between two bits and returns 0 if they are alike, else returns 1.

  Example:

  let "myvar=7" "myvar2=4" "myvar3= myvar ^ myvar2" ; echo $myvar3