Lua io.popen() doesn't work with :write and :close

[josephwright]

• I have read and acknowledged this HOWTO article:
  Submitting a MiKTeX problem report

In the MiKTeX, running texlua with input

io.popen("echo","w"):write("y"):close()

yields the error

 attempt to index a nil value

In TeX Live, the same construct is fine. Removing either the 'payload' of write (using an empty string) or removing the close resolves the error, but of course then isn't what is wanted.

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Initially reported against l3build: latex3/l3build#303

[edocevoli]

Thank you, this has been fixed. Please get the latest updates.