UNIX/ Linux | BC Commands | Exp - 6

BC Command in UNIX/ Linux

bc command is used for command line calculator. It is similar to basic calculator by using which we can do basic mathematical calculations.
Arithmetic operations are the most basic in any kind of programming language. Linux or Unix operating system provides the bc command and expr command for doing arithmetic calculations. You can use these commands in bash or shell script also for evaluating arithmetic expressions.

Syntax:

bc [ -hlwsqv ] [long-options] [ file ... ] 

Options:
-h, {- -help } : Print the usage and exit
-i, {- -interactive } : Force interactive mode
-l, {- -mathlib } : Define the standard math library
-w, {- -warn } : Give warnings for extensions to POSIX bc
-s, {- -standard } : Process exactly the POSIX bc language
-q, {- -quiet } : Do not print the normal GNU bc welcome
-v, {- -version } : Print the version number and copyright and quit

The bc command supports the following features:

Arithmetic operators

Increment or Decrement operators

Assignment operators

Comparison or Relational operators

Logical or Boolean operators

Math functions

Conditional statements

Iterative statements

1. Arithmetic Operators

Examples:

Input : $ echo "12+5" | bc
Output : 17

Input : $ echo "10^2" | bc
Output : 100

2. Assignment Operators

The list of assignments operators supported are:

• var = value : Assign the vale to the variable
• var += value : similar to var = var + value
• var -= value : similar to var = var – value
• var *= value : similar to var = var * value
• var /= value : similar to var = var / value
• var ^= value : similar to var = var ^ value
• var %= value : similar to var = var % value

Examples:

Input: $ echo "var=10;var" | bc
Output: 10

3. Increment Operators

There are 2 kinds of increment operators:

• ++var : Pre increment operator, variable is increased first and then result of variable is stored.
• var++ : Post increment operator, result of the variable is used first and then variable is incremented.

Examples:

Input: $ echo "var=10;++var" | bc
Output: 11

4. Decrement Operators

There are 2 kinds of decrement operators:

• – – var : Pre decrement operator, variable is decreased first and then result of variable is stored.
• var – – : Post decrement operator, result of the variable is used first and then variable is decremented.

Examples:

Input: $ echo "var=10;--var" | bc
Output: 9

5. Comparison or Relational Operators

Relational operators are used to compare 2 numbers. If the comparison is true, then result is 1. Otherwise(false), returns 0. These operators are generally used in conditional statements like if.
The list of relational operators supported in bc command are shown below:

• expr1<expr2 : Result is 1 if expr1 is strictly less than expr2.
• expr1<=expr2 : Result is 1 if expr1 is less than or equal to expr2.
• expr1>expr2 : Result is 1 if expr1 is strictly greater than expr2.
• expr1>=expr2 : Result is 1 if expr1 is greater than or equal to expr2.
• expr1==expr2 : Result is 1 if expr1 is equal to expr2.
• expr1!=expr2 : Result is 1 if expr1 is not equal to expr2.

Examples:

Input: $ echo "10>5" | bc
Output: 1

Input: $ echo "1==2" | bc
Output: 0

6. Logical or Boolean Operators

Logical operators are mostly used in conditional statements. The result of the logical operators is either 1(TRUE) or 0(FALSE).

• expr1 && expr2 : Result is 1 if both expressions are non-zero.
• expr1 || expr2 : Result is 1 if either expression is non-zero.
• ! expr : Result is 1 if expr is 0.

Examples:

Input: $ echo "10 && 5" | bc
Output: 1

Input: $ echo "0 || 0" | bc
Output: 0

Input: $ echo "! 0" | bc
Output: 1

7. Mathematical Functions

The built-in math functions supported are :

• s (x): The sine of x, x is in radians.
• c (x) : The cosine of x, x is in radians.
• a (x) : The arctangent of x, arctangent returns radians.
• l (x) : The natural logarithm of x.
• e (x) : The exponential function of raising e to the value x.
• j (n,x) : The bessel function of integer order n of x.
• sqrt(x) : Square root of the number x. If the expression is negative, a run time error is generated.

In addition to the math functions, the following functions are also supported :

• length(x) : returns the number of digits in x.
• read() : Reads the number from the standard input.
• scale(expression) : The value of the scale function is the number of digits after the decimal point in the expression.
• ibase and obase define the conversion base for input and output numbers. The default for both input and output is base 10.
• last (an extension) is a variable that has the value of the last printed number.

Examples:

Input:  
$ pi=`echo "h=10;4*a(1)" | bc -l`
$ echo $pi
Output: 3.14159265358979323844

8. Conditional Statements

Conditional Statements are used to take decisions and execute statements based on these decisions. bc command supports the if condition.

Syntax:

if(condition) {statements} else {statemnts}

Example:

Input: $ echo 'n=8;m=10;if(n>m) print "n is greater" else print "m is greater" ' | bc -l
Output: m is greater

9. Iterative statements

bc command supports the for loop and while loop for doing iterations.
Syntax:

for(assignment; condition; updation)
{
      statements.....
      .......
      ........
}

OR

while(condition)
{
      statements.....
      .......
      ........
}

Examples:

Input: $ echo "for(i=1; i<=10; i++) {i;}" | bc
Output: 
1
2
3
4
5
6
7
8
9
10

Input: $ echo "i=1;while(i<=10) {i; i+=1}" | bc
Output: 
1
2
3
4
5
6
7
8
9
10

10. Functions :

Functions provide a method of defining a computation that can be executed later. Functions in bc always compute a value and return it to the caller. Function definitions are “dynamic” in the sense that a function is undefined until a definition is encountered in the input. That definition is then used until another definition function for the same name is encountered. The new definition then replaces the older definition.

Syntax:

define name (parameters) 
{
        statements.......
        .......
        ........
        return statement

} 

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Problem Statement

Unix / Linux command to use, carry out mathematical operations.

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