Programming principle:
1, the programming is completed
the drive hardware default can not be used
CPU control hardware
needed instruction communication between different manufacturers of hardware devices, drivers will need to be "translated"
classification of programming languages:
high-level language, ultra-high-level language needs translated into a computer readable language (binary instructions)
interpreted - progressive translation, line by line the shell
the bash filename.sh the -X-line execution
of compiled - a compiler, all execution
program instructions = + data
Object-oriented - focusing the programming language of the data
-oriented process - focus on command
programming language implementation:
1, the order of execution
of a
two cycle execution --FOR (traverse) while (loop condition) an until (and while the opposite)
3, run the - branch if case
2, shell scripting language introduced
advantages: Call os (operating system) command line to achieve all the features
Cons: no library calls (to distinguish Python)
shell scripts include: 1, command 2, the variable (global variables, local variables, pass parameters )
3, the logic
shell of the first sentence (to be written)
#! / bin / bash-- defined script interpreter
#! / usr / bin / Python
/ etc / shells-- view the current system to support the shell program
echo $ SHELL - view the current shell program sessions
/ etc / passwd-- developed to support the user's default shell program (/ sbin / nologin)
shell execution:
1, bash command to execute the script
-n see a shell script logic error (Note: the word may be wrong no matter)
-x progressive script execution (easy troubleshooting)
2, authorize chmod + x filename. sh
using the full path to execute the script, you can
3, the variable
environment variables to see and set env
local variable declare command - Define variable type
local variable used in the function of the local
variable types:
numeric:
1. int Integer
2. float a float
3. Boolean 01 (true and false) (True False)
string:
1. ordinary characters and strings
2. array
Classification of programming languages:
a strongly typed language - the value must be defined in order to carry out the processing operation or
a weakly typed language - programming language may automatically identify the type of variables
[polymorphic data having a plurality of attributes, the properties depend on the final use and it computation] data
transmission parameters
$? - on a command execution status 0 1-255 correct errors
$ 1
$ 2
...
$ {10} - - {10} $ 1 $ incoming data following the command script, a space delimiters
$ # - parameter statistic pass amount $ # $ {}
$ * - indicates that all transmission parameters, all of the transmission parameters output as a string
$ @ - represents a pass all the parameters, all the output parameter passing in a list of
defined variable format:
NAME = of VALUE (like a howl assignment, etc. howl Analyzing two)
command defined variable types declare
declare -ia = 10 integer int () STR ()
declare arrays -a
variables command:
1. underlined specify the variable name
2. hump naming
4, test file test, to determine the conditions
in the script, we need to make the statement branch; it plainly, is to do judgment
judgment is to use the test command to achieve;
using the format:
1, test [the Option] File
2, [conditional statement]
common test options:
comparison options:
-eq equal
-ne not equal
-gt greater than
-ge greater than or equal
-lt less than
-le less
Analyzing options:
-f whether ordinary file
if the file exists -e
-d whether directory file
-L whether the linked file
-r -w -x whether. . . Permissions
associated option:
-o or
-a with
! Non-
5, logic operations
And &&
and ||
non! =
This logical operator, before and after docking commands are present alone
6, an arithmetic operation
the let +. 1. 1
the let A = +. 1. 1
echo A $
expr. 1 *. 1
expr. 1 * 10
$ [$. 1 +10]
A = $ [. 3 + 2]
echo $ A
$ ((. 1 $ / $ 2))
A = $ ((] 3/2))
echo $ A