Shell script Programming {1} per day

Variable definition and use

$var =value------don't add spaces around the equals sign

$echo $var--$var to reference a variable

$age = 20--Variable assignment

$echo "She is $age"--reference variable in string, ${age}, can distinguish variable boundary

Environment variables

$echo ${path}--like the PATH variable under win

$PATH = "$PATH:/home/user/jdk1.6.1/bin"

$export PATH-A script execution that can specify environment variables, modify or delete environment variables, only valid for this script execution, not permanently valid

Other uses of variables

$var =123456

$echo ${#var}--Get the length of the variable

$echo $SHELL--Displays the current SHELL version information

A simple if operation

if [$UID-ne 0] Then echo "not Root." Else echo "Root User." fi

Note: If the Terminator is fi, this notation is more common in Linux. -ne,-eq,-gt,-lt is used to compare integers. ==,!= is used to compare characters. There is a space between if and [. $UID is the ID of the current logged-on user.

A simple operation

Num1=1;

num2=2;

Let result=num1+num2;

Echo $result

Note: Using let for simple operations, floating-point numbers are not supported.

Mathematical Operations advanced Tools BC

echo "4*0.11" | BC-Output:. 44. | For the pipe symbol, the previous processing output as the next input.

No=8

echo "obase=2; $no" | BC-output Result: 1000. Obase:out-base, Output binary.

no=1000

echo "obase=10;ibase=2; $no" | BC-Output: 8.ibase:in-base, input binary.

Note: Using BC parameters, we can specify the binary, complete the conversion between the binary value.

echo "sqrt (100)" | BC--Open square

echo "10^2" | BC-the second party

Shell script Programming {1} per day