echo true

1, determine if the folder existsif[-d/home/q/www];then Echo"true";ElseEcho"false"; Fi (folder exists in the system/home/q/www)2, determine whether the file existsif[-E/ETC/PASSWD];then Echo"true";ElseEcho"false"; Fiif[-F/ETC/PASSWD];then Echo"true";

1. Conceptually"[[" is a keyword, and many shells (such as ash BSH) do not support this approach. Ksh, Bash (reportedly introduced support for [[support] from 2.02 onwards."[" is a command that is equivalent to test and is supported by most shells.

In addition to the following code, we also need to talk about floating point numbers. float is an approximate number. for example, in java or js, 0.1 is added 10 times, and the result is 1.0000001 instead of 1. In addition to the following code, we

Shell script file test operators and integer comparatorsOriginal: http://www.cnblogs.com/Steward-Xu/p/6722592.htmlFirst, the file test operator:In writing the test expression is, you can use the file to test the operator.　　　　More parameters can help

Php Boolean data type and process-controlled data type conversion Boolean data type is the simplest data type. It can be TRUE or FALSE, and keywords are case-insensitive. To explicitly convert an & #20540; to a boolean type, use (bool) or (boolean)

Php Boolean data type and process-controlled data type conversion Boolean data type is the simplest data type. It can be TRUE or FALSE, and keywords are case-insensitive. To explicitly convert an & #20540; to a boolean type, use (bool) or (boolean)

PHP Boolean data types and process-controlled data type conversions The Boolean is the simplest type of data. can be true or false, and the keyword is not case-sensitive. To explicitly convert a value to a Boolean type, use (bool) or (Boolean) to

PHP Process Control statements and data type conversions in conditional judgments PHP's Process Control statements include loop body statements and branch judgment statements. The loop operation consists of three sets of statements, namely while,

Shell Learning Notes# #变量# #普通变量:EG1:Name=axeEcho $nameps. equals two times cannot have a space, otherwise it will be an error.EG2:Name= "Axe Prpr"Echo $nameOrName= ' Axe PRPR 'Echo $namePS. Double quotes can refer to other variables, single

1. about Files and directories-F to determine if an ordinary file exists-D to determine if a directory exists-B Determine if a file is a block device-C Determine if a file is a character device-S to determine if a file is socket (pending correction)-

An article that understands Shell scripts, Shell scripts use the Shell command interpretation function to parse a plain text file and then execute these functions. It can also be said that Shell scripts are a collection of commands.Shell can be

First, Introduction[equivalent to test, which is the internal command of bash, the coreutils package for the Gnu/linux system usually takes/usr/bin/test and/usr/bin/[commands. If we don't specify the absolute path, we usually use Bash's own commands.

Judging the existence of variables isset($var);//只判断是否有这个变量，变量存在就是 TURE； The judging variable is empty ！empty($var);//“”，0，“0”，NULL，FALSE$var; 和没有任何属性的对象在用 empty判断时，都是空的，返回TURE； To determine if False if(0false){echo"true";}

" Focus , in which case we would treat other types of values as false for bool values:"1.0 of the integer type is treated as a pseudo-value of bool, and any non-0 integral type is considered true2. Floating point 0.0 no matter how many of the

1. What is a shell script?It is a scripting language, not a programming language.You can use some logical judgments, loops, and other syntax.You can customize the sub-function, which is a collection of system commands.Shell scripts enable automated

SQLAlchemy Introduction SQLAlchemy is an open-source software in the Python programming language. Provides a SQL Toolkit and object-relational mapping (ORM) tool that uses the MIT license release. SQLAlchemy "Implements a complete enterprise-class

Sample1# coding=gbkfrom SQLAlchemy Import *from sqlalchemy.orm Import *engine = Create_engine (' sqlite:///./sqlalchemy.db ', echo =true) metadata = metadata (engine) ' CREATE TABLE ' users_table = Table (' Users ', metadata,

One: SqlAlchemy ORMOrm:object relational Mapping Object Relational mapping is a program technology that enables the conversion of data between different types of systems in an object-oriented programming languageSQLAlchemy is an ORM framework in the

Brief introduction:Description: This module is primarily used to map a relational database table to a class of py, the row maps to an instance of the Py class, and the column maps to the properties of the Py instance, because it is compatible with

Advanced Bash-scripting Guide (18): [[] and [] some special cases, bashscripting The example selected in this article is from the book "Advanced Bash-scripting Gudie", translated by Yang chunmin Huang Yi   For example, [1-eq 1] & [-n "'echo true 1> &