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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: 

以下是当shell读取或执行一个命令时所进行操作的的一个简要描述，shell将做以下事情：

# Reads its input from a file (see [[#Shell Scripts|Shell Scripts]]), from a string supplied as an argument to the -c invocation option (see [[#Invoking Bash|Invoking Bash]]), or from the user’s terminal. 
#: 从文件读取它的输入（参看[[#Shell Scripts|Shell Scripts]]），
# Breaks the input into words and operators, obeying the quoting rules described in [[#Quoting|Quoting]]. These tokens are separated by metacharacters. Alias expansion is performed by this step (see [[#Aliases|Aliases]]). 
# Parses the tokens into simple and compound commands (see [[#Shell Commands|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).