How to Close File Descriptors Above 9 in Dash Shell
Attempting to close a file descriptor above 9 in Dash using exec 10<&- results in a 10: not found error because Dash's POSIX lexer only recognizes single-digit file descriptors (0–9) in redirection operators. This guide explains the exact parser limitation, why FDs 10+ are reserved for internal shell state, and how to safely close inherited file descriptors using close_range, Python, or Perl wrappers.
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Rajesh Rai