Principles of Programming
1. Introduction to Programming
drive:
1, the hardware default can not be used;
2, the need for command communication between different hardware device manufacturers, we need drivers to "translate";
3, more close to hardware development engineer, to learn "assembly language"; and "assembly language" is limited by the manufacturer; c c ++ is the underlying assembly language;
Now based on high-level language programming, as well as ultra-high-level language, better enable programmers to implement programming
Programming languages Category:
High-level language, ultra-high-level language to be translated into computer-readable language (binary instructions)
Interpreted - translated line by line, line by line shell python java
bash -x filename.sh line by line execution and output
Compiled - once compiled, all of the implementation c language c ++ c # java
Object-oriented - focusing on the data programming language
Process oriented - focused on the programming language instructions
Programming language implementation:
[] Line by line
1, the order of execution
2, the loop executes - * for (traverse) while (loop condition) an until (and while the opposite)
3, choose to perform - Branch if case *
2.shell scripting language introduced
Advantages: call the command os (operating system) of the line to all the functions;
Cons: no library calls (to distinguish python)
shell scripts include:
Command * (very important)
Variables (the global variables, local variables, local variables, parameter passing)
Logic
shell first words! ! ! (Must be written)
#! / Bin / bash - defined script interpreter (# is generally considered a comment line, where special) shebang
#！/usr/bin/python
/ Etc / shells to view the current program supported by the system shell
echo $ SHELL view the current session of the shell program
/ Etc / passwd developed to support the user's default shell program (/ sbin / nologin)
shell execution:
1. bash command to execute the script
-n View logic errors shell script (note: not a word wrong)
-x Progressive script execution (easy troubleshooting)
2. Authorized chmod u + x filename.sh
Use the full path to the script execution
if id $* &> /dev/null;then
echo "The user already exists."
else
for i in $*;do
useradd $i
echo”123456”|passwd –stadin “$i” &>/dev/null
done
exit 0
be
3. Variables
Environment Variables
Declare a local variable command - Define variable type
Local local variables used in the function
Variable Types
Numeric: 1, int Integer
2, float type
3, 01 Boolean (true or false)
String: 1, ordinary characters and strings
Programming languages Category:
Strongly typed language - the value must be defined in order to process or operation
A weakly typed language - programming language may automatically identify the type of variable
[Polymorphism: a data having a plurality of attributes, properties depend on the final use of the data and calculation of his]
Parameter passing
$? Command execution status of 0 on a 1-255 correct errors
$ 1 $ 2 $ {...} 10 incoming data command script later, a space for the separator
$ # Amount of statistical parameters passed $ {$ #}
$ * Means all transmission parameters, all the parameters passed to the output of string
$ @ Means all transmission parameters, all the parameters output in the form of a list of
Define the variable format:
NAME = value (without spaces, like a howl assignment, etc. howl two determination)
We declare variables defined by the type of command
declare -i integer
declare -a array
Variable name:
Underlined specify the variable name
Hump naming
4.test file test, conditional
In the script, we need to branch statement; it means making a judgment, judgment is to use the test command to achieve
Using the format:
1. test[option]file
2. [conditionals] Note: There are two spaces
Common test options:
Compare options:
-eq equal
-ne not equal
-gt greater than
-ge and large
-lt less than
-le and small
Determine options:
-f determine whether a regular file
-d whether the catalog file
-L whether the linked file
read -r -w -x write operation
Associated option:! -O or -a with non
5. logic operation
And && are true is true
Or both have a really true ||
non! =
The logical operator is present before and after the abutting a separate command
[ $? -eq 0 ] && exit 0 || exit 1
6. Arithmetic
let 1+1
expr 1*1
$[$1+10]
$(($1/$2))
+ - * / %