"cmd: command not found" from "start" command (open directory in Windows Explorer) in git bash?

I had a similar problem because my path had %SystemRoot%\system32 included. It turns out that the env variable %SystemRoot% is not statically defined, but automatically included in the environment when starting cmd.exe or power shell. Since MINGW64's bash is neither, it just saw %SystemRoot%/system32 and could not traverse that to find cmd.exe.

Changing path to use C:\Windows\System32 cured this.

The git installer adds C:\Program Files\Git\cmd to Window's PATH environment variable.

In some PC configurations, this may not be sufficient for all git execution commands to run. For example, I faced the situation where git fetch executed fine, but git help fetch produced the error /usr/bin/start: line 8: cmd not found

Following #mklement0's advice, after adding C\Windows\System32 to Window's PATH environment variable, then all git commands executed for me without error.

Try appending ;C\Windows\System32 to your Window's PATH environment variable as follows:

• Open Windows Explorer, right-click on your Computer icon, and select 'Properies'. The System Control Panel opens. Window Explorer
• Select the 'Advanced system setting' link on the left panel. The System Properties window opens. System Control Panel
• Select the 'Environment Variables...' button at the bottom of the window. The Environment Variables window opens. System Properties
• The lower panel is the 'System variables' section. In this section, scroll down and select 'Path'. Then, click on the 'Edit...' button. A small window opens where you can edit the Path variable. Path Environment Variable
• While not forgetting the ; add the following to the end of the 'Variable value' text: ;C:\Windows\System32