009-the-bc-command.md

The bc command

The bc command provides the functionality of being able to perform mathematical calculations through the command line.

Examples:

1 . Arithmetic:

Input : $ echo "11+5" | bc
Output : 16

2 . Increment:

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

Input: $ echo "var=3;++var" | bc
Output: 4

3 . Decrement:

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

Input: $ echo "var=3;--var" | bc
Output: 2

4 . Assignment:

• var = value : Assign the value 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

Input: $ echo "var=4;var" | bc
Output: 4

5 . Comparison or Relational:

• If the comparison is true, then the result is 1. Otherwise,(false), returns 0
• 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.

Input: $ echo "6<4" | bc
Output: 0

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

6 . Logical or Boolean:

• 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.

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

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

Syntax:

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

Additional Flags and their Functionalities:

Note: This does not include an exhaustive list of options.

Short Flag	Long Flag	Description
-i	--interactive	Force interactive mode
-l	--mathlib	Use the predefined math routines
-q	--quiet	Opens the interactive mode for bc without printing the header
-s	--standard	Treat non-standard bc constructs as errors
-w	--warn	Provides a warning if non-standard bc constructs are used

Notes:

1. The capabilities of bc can be further appreciated if used within a script. Aside from basic arithmetic operations, bc supports increments/decrements, complex calculations, logical comparisons, etc.
2. Two of the flags in bc refer to non-standard constructs. If you evaluate 100>50 | bc for example, you will get a strange warning. According to the POSIX page for bc, relational operators are only valid if used within an if, while, or for statement.