Technical tutorials, command syntax, and practical examples for Command Line.
Learn how standard input, standard output, and standard error work in Linux. Explore file descriptors, redirection operators, pipes, and practical commands for managing command output and error logs.
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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