expr Command in Linux with Examples

DESCRIPTION

The expr command reads the Expression parameter, evaluates it, and writes the result to standard output.

You must apply the following rules to the Expression parameter:

Separate each term with blanks.
Precede characters special to the shell with a \ (backslash).
Quote strings containing blanks or other special characters.
Integers may be preceded by a unary hyphen. Internally, integers are treated as 32-bit, twos complement numbers.

Note: The expr command returns 0 to indicate a zero value, rather than the null string.

SYNOPSIS

expr Expression

Expression

OPERATORS

The valid operators are listed below, grouped in decreasing order of precedence:

– + ~ !
Unary minus, unary plus, bit-wise NOT, logical NOT. None of these operands may be applied to string operands, and bit-wise NOT may be applied only to integers.
* / %
Multiply, divide, remainder. None of these operands may be applied to string operands, and remainder may be applied only to integers. The remainder will always have the same sign as the divisor and an absolute value smaller than the divisor.
+ –
Add and subtract. Valid for any numeric operands.
<< >>
Left and right shift. Valid for integer operands only. A right shift always propagates the sign bit.
< > <= >=
Boolean less, greater, less than or equal, and greater than or equal. Each operator produces 1 if the condition is true, 0 otherwise. These operators may be applied to strings as well as numeric operands, in which case string comparison is used.
== !=
Boolean equal and not equal. Each operator produces a zero/one result. Valid for all operand types.
&
Bit-wise AND. Valid for integer operands only.
^
Bit-wise exclusive OR. Valid for integer operands only.
|
Bit-wise OR. Valid for integer operands only.
&&
Logical AND. Produces a 1 result if both operands are non-zero, 0 otherwise. Valid for boolean and numeric (integers or floating-point) operands only.
||
Logical OR. Produces a 0 result if both operands are zero, 1 otherwise. Valid for boolean and numeric (integers or floating-point) operands only.
x?y:z
If-then-else, as in C. If x evaluates to non-zero, then the result is the value of y. Otherwise the result is the value of z. The x operand must have a numeric value.
See the C manual for more details on the results produced by each operator. All of the binary operators group left-to-right within the same precedence level. For example, the command

expr 4*2 < 7 returns 0. The &&, ||, and ?: operators have ``lazy evaluation'', just as in C, which means that operands are not evaluated if they are not needed to determine the outcome. For example, in the command expr {$v ? [a] : [b]} only one of [a] or [b] will actually be evaluated, depending on the value of $v. Note, however, that this is only true if the entire expression is enclosed in braces; otherwise the Tcl parser will evaluate both [a] and [b] before invoking the expr command. MATH FUNCTIONS

It supports the following mathematical functions in expressions:

abs(arg)
Returns the absolute value of arg. Arg may be either integer or floating-point, and the result is returned in the same form.
acos(arg)
Returns the arc cosine of arg, in the range [0,pi] radians. Arg should be in the range [-1,1].
asin(arg)
Returns the arc sine of arg, in the range [-pi/2,pi/2] radians. Arg should be in the range [-1,1].
atan(arg)
Returns the arc tangent of arg, in the range [-pi/2,pi/2] radians.
atan2(x, y)
Returns the arc tangent of y/x, in the range [-pi,pi] radians. x and y cannot both be 0.
ceil(arg)
Returns the smallest integer value not less than arg.
cos(arg)
Returns the cosine of arg, measured in radians.
cosh(arg)
Returns the hyperbolic cosine of arg. If the result would cause an overflow, an error is returned.
double(arg)
If arg is a floating value, returns arg, otherwise converts arg to floating and returns the converted value.
exp(arg)
Returns the exponential of arg, defined as e**arg. If the result would cause an overflow, an error is returned.
floor(arg)
Returns the largest integral value not greater than arg.
fmod(x, y)
Returns the floating-point remainder of the division of x by y. If y is 0, an error is returned.
hypot(x, y)
Computes the length of the hypotenuse of a right-angled triangle (x*x+y*y).
int(arg)
If arg is an integer value, returns arg, otherwise converts arg to integer by truncation and returns the converted value.
log(arg)
Returns the natural logarithm of arg. Arg must be a positive value.
log10(arg)
Returns the base 10 logarithm of arg. Arg must be a positive value.
pow(x, y)
Computes the value of x raised to the power y. If x is negative, y must be an integer value.
rand()
Returns a floating point number from zero to just less than one or, in mathematical terms, the range [0,1). The seed comes from the internal clock of the machine or may be set manual with the srand function.
round(arg)
If arg is an integer value, returns arg, otherwise converts arg to integer by rounding and returns the converted value.
sin(arg)
Returns the sine of arg, measured in radians.
sinh(arg)
Returns the hyperbolic sine of arg. If the result would cause an overflow, an error is returned.
sqrt(arg)
Returns the square root of arg. Arg must be non-negative.
srand(arg)
The arg, which must be an integer, is used to reset the seed for the random number generator. Returns the first random number from that seed. Each interpreter has it’s own seed.
tan(arg)
Returns the tangent of arg, measured in radians.
tanh(arg)
Returns the hyperbolic tangent of arg.

Exit Status

This command returns the following exit values:

0
The Expression parameter evaluates to neither null nor 0.
1
The Expression parameter evaluates to null or 0.
2
The Expression parameter is not valid.
>2
An error occurred.

EXAMPLES

1. To modify a shell variable, enter:

 COUNT=`expr $COUNT + 1`

This adds 1 to the shell variable $COUNT. The expr command is enclosed in grave accents, which causes the shell to substitute the standard output from the expr command into the COUNT= command. The $COUNT variable must be initialized before using.

2. To find the length of a shell variable

$ echo `expr $VAR : ".*"`

Note : If the $VAR variable is set to the null string or contains any white space (blanks or tabs), then the command displays the error message expr: syntax error.

3. Perform string matching operations

expr command helps us to perform different levels of string matching operations with the operator ‘:’ as shown below,

 
$ expr linux : lin
3
 
 
$ expr linux : linx
0
 
 
$ expr linux : '.*'
5

4. Compare the two expressions

$ var1='10'
$ var2='20'
 
$ expr $var1 = $var2
0
 
$ expr $var1 \< $var2
1
 
$ expr $var1 \!= $var2
1

5. Perform the integer arithmetic operations

$ expr 5 \* 2
10