[issue4925] Improve error message of subprocess

[David W. Lambert]

David W. Lambert <lambertdw at corning.com> added the comment:

Related, but outside python realm, this error likewise confuses:

$ cat <<EOF > s.sh
#! invalid path
echo hi
EOF
$ ./s.sh 
zsh: no such file or directory: ./s.sh

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nosy: +LambertDW

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<http://bugs.python.org/issue4925>
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