error: Cannot find cmake, ensure it is installed and in the path

You have to install Cmake.

What OS are you running on. Installing CMake can be installed for windows or linux.
However for windows you also have to be sure to have a compiler and all the required C files and header files for the project that you try to install.
Installing modules, that need compilation under windows can be a little frustrating. Under linux there are asome pitfalls  but it's normally easier.

What exactly do you try to install?
Are you sure, that there isno ready made binary version available?

1. Attaching the document to install cmake.exe at windows using cygwin
2. Verify PATH environment variable having the directory of cmake.exe or cmake
Example using bash:

$ /usr/bin/which cmake
/bin/cmake
$ echo $PATH | /usr/bin/tr ":" "\n" | /bin/grep -E "^\/bin"
/bin

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Since /bin directory present in PATH environment variable hence /usr/bin/which command displaying related path.

@Windows
     Press windows r

C:\Windows\System32\rundll32.exe sysdm.cpl,EditEnvironmentVariables

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    Check Path environment variable there.
Open C:\Windows\System32\cmd.exe

C:\Users\Public> CD %USERPROFILE%
C:\Users\murugesandins> DIR/S /B cmake.exe
C:\Users\murugesandins\cygwin\bin\cmake.exe
C:\Users\murugesandins>

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cygwin_cmake_installation.docx