From Seo Wiki - Search Engine Optimization and Programming Languages
Syntax: expr (expression)
expr evaluates integer or string expressions, including pattern matching regular expressions. Most of the challenge posed in writing expressions is preventing the command line shell from acting on characters intended for expr to process.
The operators available
- for integers: addition, subtraction, multiplication, division and modulus
- for strings: find substring, find regular expression, find a set of characters in a string, length of string
- for either: comparison (equal, not equal, less than, etc.)
Also, boolean expressions involving and and or, such as
expr length "abcdef" "<" 5 "|" 15 - 4 ">" 8
outputs "1". This is because length "abcdef" is 6, which is not less than 5 (so the left side of the | returns zero). But 15 minus 4 is 11 and is greater than 8, so the right side is true, which makes the or true, so 1 is the result. The program exit status is zero for this example.
For pure arithmetic, it may be more convenient to use bc, e.g.
echo "3*4+14/2" | bc
since it accepts the expression as a single argument.