tail: exists precheck masks permission errors

[sylvestre]

Component

tail

Description

uutils checks path.exists() before opening the file. Path::exists() returns false on metadata errors (including EACCES), so a permission error is reported as “No such file or directory” and the open is never attempted. GNU tail attempts the open and reports the real errno.

Test / Reproduction Steps

# As root:
mkdir /tmp/noexec
echo secret > /tmp/noexec/file
chmod 000 /tmp/noexec

# As unprivileged user:
tail -n 1 /tmp/noexec/file
# GNU: "tail: cannot open '/tmp/noexec/file' for reading: Permission denied"
# uutils: "tail: cannot open '/tmp/noexec/file' for reading: No such file or directory"

Impact

Incorrect diagnostics and follow/retry behavior can break scripts that rely on accurate error reporting.

[frgmntedflower]

Hi! I'd like to tackle this.