为什么提示用户输入字符串/选项后，字符串比较无法正常工作?

对于打印空白行，最好使用echo/而不是echo.，因为echo.可能会失败，并且由于Windows命令解释程序会搜索与模式echo.*相匹配的文件而导致速度变慢在DosTips论坛文章 ECHO中.未能输入文本或空白行-而是使用ECHO/.如果用户必须输入特定键，则命令 CHOICE 比set /P VariableName=Prompt text好得多. CHOICE 命令不允许用户输入批处理文件编写器不需要的内容，因此对于选择菜单而言更加安全.用%USERNAME%引用的当前用户的帐户名也可以包含空格字符.因此，强烈建议将包含%USERNAME%的整个字符串始终用双引号引起来.字符串比较右侧的 "%USERNAME%"要求左侧的字符串也用双引号引起来，因为命令 IF 会比较两个包含双引号的字符串.因此，条件if /I !player! == "%USERNAME%"仅当批处理文件用户使用双引号输入播放器名称(这是极不可能的)时，才为true.双引号也必须在左侧使用.用双引号引起来的两个比较字符串周围的空格字符的数量无关紧要.在命令提示符窗口中执行以下批处理文件@echo on@setlocal EnableExtensions EnableDelayedExpansion@set "Player=<|>"if /I "!Player!"=="%SystemRoot%" echo Strings are equal.if /I "!Player!" == "%WinDir%" echo Strings are equal.if /I "!Player!" == "%Player%" echo Strings are equal.if /I "!Player!"== "!Player!" echo Strings are equal.if /I !Player! == !Player! echo Strings are equal.@endlocal输出结果if /I "!Player!" == "C:\WINDOWS" echo Strings are equal.if /I "!Player!" == "C:\WINDOWS" echo Strings are equal.if /I "!Player!" == "<|>" echo Strings are equal.Strings are equal.if /I "!Player!" == "!Player!" echo Strings are equal.Strings are equal.if /I !Player! == !Player! echo Strings are equal.Strings are equal.可以看出，比较运算符==周围的空格与命令 IF 的执行无关. Windows命令处理器在执行 IF 命令之前就已经格式化了命令行.但是要比较的字符串中的空格字符需要使用双引号，因为否则可能会由于批处理文件执行中的语法错误而导致退出批处理. 注意:命令 IF 的等号运算符==与命令 SET 的赋值运算符=不同.不要混在一起.要了解所使用的命令及其工作方式，请打开命令提示符窗口，在其中执行以下命令，并非常仔细地阅读每个命令显示的所有帮助页面. choice /? cls /? echo /? endlocal /? goto /? if /? ping /? rem /? set /? setlocal /?另请参见Microsoft文章使用命令重定向运算符 >nul的说明.Is this the proper way to write these lines of batch code with the exceptions of spaces and unneeded percent signs?:nameclsecho now that we've got your color figured out, what about your name?echo simply type the name you want for your character into the space belowecho (6 char max)echo.set /p %player% =clsecho so you want your name to be %player% ?echo.echo 1) yesecho 2) noset /p %namechoice% =if %namechoice% == 1 goto checkif %namechoice% == 2 goto name:checkif /I %player% == %username% (goto gamestart) else goto suprise:supriseThe player name is not output after batch user entered it.And the string comparisons with check and name are also not working.The command line if %namechoice% == 1 goto check results in break of batch file execution with error message: 解决方案 The main mistake is a simple syntax issue:Environment variables are defined with just specifying the variable name without percent signs and with no space character before the equal sign.So wrong isset /p %player% =set /p %namechoice% =because those two lines are expanded during preprocessing phase before really executing the command SET toset /p =set /p =in case of environment variables player and namechoice are not already defined. See Why is no string output with 'echo %var%' after using 'set var = text' on command line? for details about how to define an environment variable right. It explains also why the space character left to equal sign on variable definition becomes part of the variable name which is nearly always unwanted by batch file writer.Such simple syntax issues can be easily seen on running a batch file without @echo off at top of the batch file or with this line modified to @echo on or commented out with ::@echo off (invalid label) or rem @echo off (remark command) from within a command prompt window by entering name of the batch file with full path in double quotes instead of double clicking on the batch file.What makes the difference?With @echo off the command lines are not printed into the console window after preprocessing (expanding environment variables) before really executing them. This is the wanted behavior when batch file development finished. But during development and testing of a batch file it is definitely better to get displayed what is really executed by Windows command interpreter to find coding mistakes.On double clicking a batch file cmd.exe is started to execute the batch file with option /C for closing the console window automatically when batch file execution terminated independent on success or error of execution. This makes it not possible to see for example syntax errors output by Windows command interpreter which result in an immediate exit of batch file execution. Therefore it is advisable during batch file development to run it from within a manually opened command prompt window as in this case cmd.exe is started with option /K to keep the console window open even after batch processing finished, except the batch file uses command exit without parameter /B. This makes it possible to see also the error message of an error which caused an unexpected exit of batch processing.Later when batch file works as expected, the first line can be @echo off again and of course the batch file can be started with a double click. But during batch file development it is definitely better to always run the batch file from within a command prompt window. The up/down arrow keys can be used to scroll through the list of entered strings which makes it also possible to re-enter for example the player name easily again.Here is the batch code rewritten with several improvements and comments:@echo offsetlocal EnableExtensions EnableDelayedExpansionrem Define a too long player name before prompting the user for the playerrem name. This too long player name is kept in case of user hits just therem key RETURN or ENTER without entering anything at all. Then test forrem entered name has not more than 6 characters. Delayed expansion is usedrem as the user could enter characters like " ! % ... which would in furtherrem batch code execution result in exiting batch processing because of syntaxrem error or in unexpected behavior on referencing player name with expansionrem before running the command.:PromptForNameclsecho Now that we've got your color figured out, what about your name?echo Simply type the name you want for your character into the spaceecho below (6 char max).echo/set "Player=No name entered"set /P "Player=Player name: "if not "!Player:~6!" == "" goto PromptForNameecho/echo/echo 1) yesecho 2) noecho/choice /C:12 /N "So you want your name to be !player!? "if errorlevel 2 goto PromptForNameif /I "!player!" == "%USERNAME%" goto GameStartecho Surpriseendlocalgoto :EOF:GameStartecho/echo Okay !Player!, let's play^^!rem Wait 3 seconds using PING instead of TIMEOUT before exiting therem batch file because the command TIMEOUT does not exist on Windows XP.%SystemRoot%\System32\ping.exe 127.0.0.1 -n 4 >nulendlocalThe comment at top explains why the environment variable Player is defined with value No name entered. The batch user has the freedom to hit just or without entering anything at all or hits by mistake one of those 2 keys before entering a name. In this case the environment variable Player is either still not defined if not defined before, or it keeps its current value if already defined before. It is not good if the user enters nothing and the environment variable Player is not defined in this case. Therefore the player name is predefined with an invalid name.The length of the entered player name is also tested on being too long.And the string entered by the user could contain batch syntax critical characters like a double quote, a percent sign, a redirection operator character (angle bracket, pipe), an ampersand, or with delayed expansion enabled an exclamation mark. To prevent an exit of batch processing caused by a syntax error by entered player name on using environment variable expansion before command line execution, the environment variable Player is referenced everywhere with usage of delayed expansion enabled at top of the batch file.For printing a blank line it is better to use echo/ instead of echo. because echo. could fail and is a little bit slower because of Windows command interpreter searches for a file matching the pattern echo.* as documented in DosTips forum article ECHO. FAILS to give text or blank line - Instead use ECHO/.The command CHOICE is much better than set /P VariableName=Prompt text if the user has to enter specific keys. The command CHOICE does not allow that the user enters something not wanted by batch file writer and is therefore much safer for a choice menu.The account name of current user referenced with %USERNAME% could contain also a space character. Therefore it is highly recommended to enclose the entire string containing %USERNAME% always in double quotes."%USERNAME%" on right side of a string comparison requires that the string on left side is also enclosed in double quotes because command IF compares the two strings with including the double quotes.For that reason the conditionif /I !player! == "%USERNAME%"would be only true if the batch file user would have entered the player name with double quotes which is very unlikely. The double quotes must be also used on left side.The number of space characters around the two compared strings enclosed in double quotes or not enclosed in double quotes does not matter.Executing in a command prompt window the following batch file@echo on@setlocal EnableExtensions EnableDelayedExpansion@set "Player=<|>"if /I "!Player!"=="%SystemRoot%" echo Strings are equal.if /I "!Player!" == "%WinDir%" echo Strings are equal.if /I "!Player!" == "%Player%" echo Strings are equal.if /I "!Player!"== "!Player!" echo Strings are equal.if /I !Player! == !Player! echo Strings are equal.@endlocalresults in the outputif /I "!Player!" == "C:\WINDOWS" echo Strings are equal.if /I "!Player!" == "C:\WINDOWS" echo Strings are equal.if /I "!Player!" == "<|>" echo Strings are equal.Strings are equal.if /I "!Player!" == "!Player!" echo Strings are equal.Strings are equal.if /I !Player! == !Player! echo Strings are equal.Strings are equal.It can be seen that the space characters around comparison operator == do not matter on execution of command IF. The Windows command processor formats the command lines pretty before executing the IF commands.But a space character in a string to compare requires the usage of double quotes because otherwise an exit of batch processing occurs most likely because of a syntax error on batch file execution.Note: The equal operator == of command IF is handled different than the assignment operator = of command SET. Don't mix them.For understanding the used commands and how they work, open a command prompt window, execute there the following commands, and read entirely all help pages displayed for each command very carefully.choice /?cls /?echo /?endlocal /?goto /?if /?ping /?rem /?set /?setlocal /?And see also the Microsoft article Using command redirection operators for an explanation of >nul. 这篇关于为什么提示用户输入字符串/选项后，字符串比较无法正常工作?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！