if: add page (#7443)

pages/windows/if.md

@@ -0,0 +1,32 @@
+# if
+
+> Performs conditional processing in batch scripts.
+> More information: <https://docs.microsoft.com/windows-server/administration/windows-commands/if>.
+
+- Execute the specified commands if the condition is true:
+
+`if {{condition}} ({{echo Condition is true}})`
+
+- Execute the specified commands if the condition is false:
+
+`if not {{condition}} ({{echo Condition is true}})`
+
+- Execute the first specified commands if the condition is true otherwise execute the second specified commands:
+
+`if {{condition}} ({{echo Condition is true}}) else ({{echo Condition is false}})`
+
+- Check whether `%errorlevel%` is greater than or equal to the specified exit code:
+
+`if errorlevel {{exit_code}} ({{echo Condition is true}})`
+
+- Check whether two strings are equal:
+
+`if {{string}} == {{string}} ({{echo Condition is true}})`
+
+- Check whether two strings are equal without respecting letter case:
+
+`if /i {{string}} == {{string}} ({{echo Condition is true}})`
+
+- Check whether a file exist:
+
+`if exist {{path/to/file}} ({{echo Condition is true}})`