expr
exprarg1 operator arg2
[operator arg3 ...
]
Evaluate arguments as expressions and print the result. Strings can be compared and searched. Arguments and operators must be separated by spaces. In most cases, an argument is an integer, typed literally or represented by a shell variable. There are three types of operators: arithmetic, relational, and logical. Exit status for expr is 0 (expression is nonzero and nonnull), 1 (expression is 0 or null), or 2 (expression is invalid).
expr is typically used in shell scripts to perform simple arithmetic, such as addition or subtraction. It is made obsolete in modern shells that have builtin arithmetic capabilities.
Use the following operators to produce mathematical expressions whose results are printed:

Add arg2 to arg1. 

Subtract arg2 from arg1. 

Multiply the arguments. 

Divide arg1 by arg2. 

Take the remainder when arg1 is divided by arg2. 
Addition and subtraction are evaluated last, unless they are
grouped inside parentheses. The symbols *
, (
,
and )
have meaning to the
shell, so they must be escaped (preceded by a backslash or
enclosed in single or double quotes).
Use relational operators to compare two arguments. Arguments can also be
words, in which case comparisons assume a
< z
and A < Z
.
If the comparison statement is true, the result is 1; if false,
the result is 0. Symbols <
and >
must be
escaped.

Are the arguments equal? 

Are the arguments ... 
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