Detailed explanation: Shell script variable judgment parameter command
Sep 02, 2024 pm 03:25 PM$n 傳遞給腳本或函數(shù)的參數(shù)。n 是一個數(shù)字,表示第幾個參數(shù)。例如,第一個參數(shù)是$1,第二個參數(shù)是$2 $? 上個命令的退出狀態(tài),或函數(shù)的返回值。成功返回0,失敗返回1 $# 傳遞給腳本或函數(shù)的參數(shù)個數(shù) $* 所有這些參數(shù)都被雙引號引住。若一個腳本接收兩個參數(shù),$*等于$1$2 $0 正在被執(zhí)行命令的名字。對于shell腳本而言,這是被激活命令的路徑 $@ 被雙引號(” “)包含時,與 $* 稍有不同。若一個腳本接收到兩個參數(shù),$@等價于$1$2 $$ 當(dāng)前shell的進程號。對于shell腳本,這是其正在執(zhí)行時的進程ID $! 前一個后臺命令的進程號
-b file 若文件存在且是一個塊特殊文件,則為真 -c file 若文件存在且是一個字符特殊文件,則為真 -d file 若文件存在且是一個目錄,則為真 -e file 若文件存在,則為真 -f file 若文件存在且是一個規(guī)則文件,則為真 -g file 若文件存在且設(shè)置了SGID位的值,則為真 -h file 若文件是軟鏈接,則為真 -k file 若文件存在且設(shè)置了”sticky”位的值 -L file 若文件為符號鏈接,則為真 -p file 若文件存在且為一已命名管道,則為真 -r file 若文件可讀,則為真 -s file 判斷文件是否存在,且是否為非空,不為空,則為真 -S file 判斷文件是否存在,且是否為套接字文件 -t file 文件描述符(默認為1)指定的設(shè)備為終端時為真 -u file 若文件存在且設(shè)置了SUID位,則為真 -w file 若文件可寫,則為真 -x file 若文件可執(zhí)行,則為真 [ file1 -nt file2 ] 若file1比file2新,或file1存在但file2不存在,則為真 [ file1 -ot file2 ] 若file1比file2老,或file2存在但file1不存在,則為真 [ file1 -ef file2 ] 若file1和file2指向相同的設(shè)備和節(jié)點號則返回,為真
-eq 兩數(shù)相等,則為真 例:if [ "$a" -eq "$b" ] -ne 兩數(shù)不相等,則為真 例:if [ "$a" -ne "$b" ] -gt a大于b,則為真 例:if [ "$a" -gt "$b" ] -ge 大于或等于,則為真 例:if [ "$a" -ge "$b" ] -lt a小于b,則為真 例:if [ "$a" -lt "$b" ] -le a小于或等于b,則為真 例:if [ "$a" -le "$b" ] 大于(需雙括號) 例:(("$a" > "$b")) >= 大于等于(需雙括號) 例:(("$a" >= "$b")) 小數(shù)據(jù)比較可使用AWK。
! [ ! false ] 返回true 邏輯否,條件為假,結(jié)果為真 -a [ $a -lt 2 -a $b -gt 5 ] 返回true 邏輯與,兩個表達式都為真,則為真 -o [ $a -lt 2 -o $b -gt 5 ] 返回true 邏輯或,只要有一個表達式為true,則為真 [ ] || [ ] 用OR來合并兩個條件 [ ] && [ ] 用AND來合并兩個條件
== 若兩個字符串相同則為真,與=等價 例:[ "str1" = "str2" ] != 若字符串不相同則為真 例:[ "str1" != "str2" ] 若str1字典排序在str2后則為真 例:[ "str1" \> "str2" ] -n 若str長度非零則為真,即非空 例:[ -n "str1" ] -z 若file長度為零,即空,則為真 例:[ -z "str1" ]
注意:在[]結(jié)構(gòu)中”
The above is the detailed content of Detailed explanation: Shell script variable judgment parameter command. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

Integrating Postman applications on CentOS can be achieved through a variety of methods. The following are the detailed steps and suggestions: Install Postman by downloading the installation package to download Postman's Linux version installation package: Visit Postman's official website and select the version suitable for Linux to download. Unzip the installation package: Use the following command to unzip the installation package to the specified directory, for example /opt: sudotar-xzfpostman-linux-x64-xx.xx.xx.tar.gz-C/opt Please note that "postman-linux-x64-xx.xx.xx.tar.gz" is replaced by the file name you actually downloaded. Create symbols

[Common Directory Description] Directory/bin stores binary executable files (ls, cat, mkdir, etc.), and common commands are generally here. /etc stores system management and configuration files/home stores all user files. The root directory of the user's home directory is the basis of the user's home directory. For example, the home directory of the user user is /home/user. You can use ~user to represent /usr to store system applications. The more important directory /usr/local Local system administrator software installation directory (install system-level applications). This is the largest directory, and almost all the applications and files to be used are in this directory. /usr/x11r6?Directory for storing x?window/usr/bin?Many

Setting the location of the interpreter in PyCharm can be achieved through the following steps: 1. Open PyCharm, click the "File" menu, and select "Settings" or "Preferences". 2. Find and click "Project:[Your Project Name]" and select "PythonInterpreter". 3. Click "AddInterpreter", select "SystemInterpreter", browse to the Python installation directory, select the Python executable file, and click "OK". When setting up the interpreter, you need to pay attention to path correctness, version compatibility and the use of the virtual environment to ensure the smooth operation of the project.

The main difference between Java and other programming languages ??is its cross-platform feature of "writing at once, running everywhere". 1. The syntax of Java is close to C, but it removes pointer operations that are prone to errors, making it suitable for large enterprise applications. 2. Compared with Python, Java has more advantages in performance and large-scale data processing. The cross-platform advantage of Java stems from the Java virtual machine (JVM), which can run the same bytecode on different platforms, simplifying development and deployment, but be careful to avoid using platform-specific APIs to maintain cross-platformity.

Understanding Nginx's configuration file path and initial settings is very important because it is the first step in optimizing and managing a web server. 1) The configuration file path is usually /etc/nginx/nginx.conf. The syntax can be found and tested using the nginx-t command. 2) The initial settings include global settings (such as user, worker_processes) and HTTP settings (such as include, log_format). These settings allow customization and extension according to requirements. Incorrect configuration may lead to performance issues and security vulnerabilities.

The installation and configuration of MySQL can be completed through the following steps: 1. Download the installation package suitable for the operating system from the official website. 2. Run the installer, select the "Developer Default" option and set the root user password. 3. After installation, configure environment variables to ensure that the bin directory of MySQL is in PATH. 4. When creating a user, follow the principle of minimum permissions and set a strong password. 5. Adjust the innodb_buffer_pool_size and max_connections parameters when optimizing performance. 6. Back up the database regularly and optimize query statements to improve performance.

Informix and MySQL are both popular relational database management systems. They perform well in Linux environments and are widely used. The following is a comparison and analysis of the two on the Linux platform: Installing and configuring Informix: Deploying Informix on Linux requires downloading the corresponding installation files, and then completing the installation and configuration process according to the official documentation. MySQL: The installation process of MySQL is relatively simple, and can be easily installed through system package management tools (such as apt or yum), and there are a large number of tutorials and community support on the network for reference. Performance Informix: Informix has excellent performance and

I have a lot of experience in participating in VSCode offline technology exchange activities, and my main gains include sharing of plug-in development, practical demonstrations and communication with other developers. 1. Sharing of plug-in development: I learned how to use VSCode's plug-in API to improve development efficiency, such as automatic formatting and static analysis plug-ins. 2. Practical demonstration: I learned how to use VSCode for remote development and realized its flexibility and scalability. 3. Communicate with developers: I have obtained skills to optimize VSCode startup speed, such as reducing the number of plug-ins loaded at startup and managing the plug-in loading order. In short, this event has benefited me a lot and I highly recommend those who are interested in VSCode to participate.
