Fundamentals of Linux Foundation--bash programming

Does the bash test have a grammar test

Bash-n file.sh

Script execution in debug mode

Bash-x file.sh

Defining global variables in the shell

Export date= ' DATE +%y%m%d '

Arithmetic operators in the shell

A=3

B=4

If you use c= $A + $B to represent the addition of strings, the result is 3+4

1. Let arithmetic operation expression

Let c= $A + $B

2. $[arithmetic operation expression]

c=$[$A + $B]

3, $ ((arithmetic operator))

c=$ (($A + $B))

4. Expr arithmetic operator, with spaces between expressions, and using command references

c= ' expr $A + $B '

Conditional test in Shell

1, integer test (binocular operation, compare two numbers, usually variables and numbers or variables and variables)

expression [$A-eq $B] (command test method, note space)

[[$A-eq $B]] (keyword test method)

Test $A-eq $B (Tests command testing method)

-GT greater than

-lt less than or equal to

-ne Not equal to

-eq equals

-ge greater than or equal to

-lt less than

Note: There is no need to use [] in addition to the above-mentioned judgment when testing.

such as: if grep "^ $USERNAME \>"/etc/passwd; then can be directly judged without using []

2. File test

-e file: Test files exist

-F File: Test files are normal files

-D File: Test whether the files are directories

-R File: Tests whether the current user has read access to the specified file

-W File: Tests whether the current user has write access to the specified file

-X file: Tests whether the current user has execute permissions on the specified file

such as: if [-f/etc/inittab] (note space)

Exit # define Exit status code

Bash Variable type

Local variable (local variable) "Scope is current shell"

Environment variable "Scope is current shell and child shell"

Positional variables

$ $

Shift N (kicks the first n position variables)

Special variables

$?: previous command execution status

$#: Number of parameters

$*: Parameter list

[email protected]: parameter list

This article from "Liang Childe" blog, please be sure to keep this source http://iyull.blog.51cto.com/4664834/1884528

Fundamentals of Linux Foundation--bash programming