![]() So, what does that really mean? In its most basic form, you separate queries from commands by function: Simply put: a query should never mutate state, while a command can mutate state but should never have a return value. Methods should return a value only if they create no side effects. ![]() It all comes down to two principles.Įvery method should either be a command that performs an action, or a query that returns data to the caller, but never both. In case it's the first time you have ever heard about this term, I encourage you to read the formal definition of CQS on Martin Fowler’s blog. Command Query Separation (CQS)īertrand Meyer devised CQS, or Command Query Separation, as part of his work on the Eiffel programming language. Subscribe to this magazine for FREE and receive all previous, current and upcoming editions, right in your Inbox. NET Core, MVC, Azure, DevOps, ALM, TypeScript, Angular, React, and more. This magazine is aimed at Developers, Architects and Technical Managers and covers C#, Patterns. This tutorial is from the DotNetCurry(DNC) Magazine with in-depth tutorials and best practices in. This will allow us to tackle a lot of these goals and to keep code readable, structured, reusable and less error prone. In this tutorial, I'll focus on how to design software using the Command Query Separation (CQS) pattern. These factors, let’s call them architectural goals, include (but are not limited to) : Reference the host that NSH was launched To cd back to the root directory of the system running NSHĬd To cd back to /tmp on the system running NSHĬd To copy /tmp/file.When you choose an architecture, a lot of factors come into play. Nexec -D ///C/Temp cmd /c "cscript /nologo myScript.vbs" To call cscript and run the myScript.vbs that is in the /C/Temp directory on the target without having to translate the NSH path /C/Temp to Windows path to C:\Temp:.To run the uname -a command against without "cding" into :.To run the OS ls command in /var/tmp/stage on :.The following table lists various tips and tricks for using NSH:Įxecute a command in a remote path on a server Where server.txt contains a list of host names (for example), one per line.Ĭheck conditions and perform actions depending on results. for TARGET in $TARGET_LIST do echo $TARGET done.Loop through a list, performing the same actions on each itemĪnother method for looping through a list, performing the same actions on each item. Note: To see if a directory does not exist, use an exclamation mark as in the following command: Note: To see if a file does not exist, use an exclamation mark as in the following command: This should be the first line of an NSH script when run on a UNIX/Linux host to identify it as NSH. It provides information on basic scripting elements such as checking if a file or directory exists, creating a for loop, or creating an if else condition. The following table provides descriptions and examples of commonly used elements within an NSH Script. To view summarized descriptions of commands and utilities, see the alphabetized table in Summarized descriptions of Network Shell commands. \"Administrators\",domain=\"%COMPUTERNAME%\"")' Host% nexec -ncq cmd /c 'wmic path win32_groupuser Verify the RSCD agent version, mapping, and license status.Įxecute a WMIC command on a remote Windows server. Host% runscript -NH -V -f /hostlist -e //host/script Host% runcmd -f /hostlist -e ps -ef | grep processĮxecute an NSH script across many servers Verify a process exists across many servers. Host% runcmd -h host 1 host 2 -e rm /file_being_deleted This feature is not available on Windows operating systems. Note: When using nexec, you can use an ampersand (&) character at the end of the command line to execute your command in the background on a UNIX or Linux machine. Remotely execute a command that lives locally on the target server. nstats - system statistics across many machines.nnet - summary of network info across many machines.nmem - summary of memory across many machines.nover - provides system-level overview across many machines.Use n commands to retrieve pertinent os-level information about servers: Host% diff //host1/directory/file //host2/directory/file Host% cp //host1/directory/file ncp //host1/directory/file -d //host1/directory1 //host2/directory2Ĭompare a file that exists on multiple hosts Host% cp -r //host1/directory //host2/directory Host% cp /directory/file //host2/directory Host% ls -l //host1/directory //host2/directoryĬopy one or more file or directories from one machine to another. List directory contents on one or many remote machines.
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