Comment check if a file exists depuis inside a fichier batch

[Clippy]

How to check if a file exists from inside a fichier batch

[ayi]

if exist <insert file name here> (
    rem file exists
) else (
    rem file doesn't exist
)

Or on a single line (if only a single action needs to occur):

if exist <insert file name here> <action>

par exemple, this opens notepad on autoexec.bat, if the file exists:

if exist c:\autoexec.bat notepad c:\autoexec.bat