Built-in Commands

The following simple-commands are executed in the shell process. Input/Output redirection is permitted. Unless otherwise indicated, the output is written on file descriptor 1 and the exit status, when there is no syntax error, is zero. Except for :, true, false, echo, command, newgrp, and login, all built-in commands accept to indicate end of options. They also interpret the option -? as a help request and print a usage message on standard error. Commands that are preceded by one or two § symbols are special built-in commands and are treated specially in the following ways:

  1. Variable assignment lists preceding the command remain in effect when the command completes.

  2. I/O redirections are processed after variable assignments. ...

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