Shell Operation (Bash Reference Manual)
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3.1.1 Shell Operation
The following is a brief description of the shell’s operation when it reads and executes a command. Basically, the shell does the following:
- Reads its input from a file (see Shell Scripts), from a string supplied as an argument to the
-cinvocation option (see Invoking Bash), or from the user’s terminal.
- Breaks the input into words and operators, obeying the quoting rules described in Quoting. These tokens are separated by
metacharacters. Alias expansion is performed by this step (see Aliases).
- Parses the tokens into simple and compound commands (see Shell Commands).
- Performs the various shell expansions (see Shell Expansions), breaking the expanded tokens into lists of filenames (see Filename Expansion) and commands and arguments.
- Performs any necessary redirections (see Redirections) and removes the redirection operators and their operands from the argument list.
- Executes the command (see Executing Commands).
- Optionally waits for the command to complete and collects its exit status (see Exit Status).