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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]]），从字符串参数以-c调用选项方式（参看[[#Invoking Bash|Invoking Bash]]），或者从用户终端。
# 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]]). 
#: 断句，把相关的输入分解成words和操作符，它遵循[[#Quoting|Quoting]]中的引用规则。这些tokens会被元字符分开。别名扩展将按照[[#Aliases|Aliases]]步骤被执行。
# Parses the tokens into simple and compound commands (see [[#Shell Commands|Shell Commands]]). 
#: 这些tokens将被解析为一些简单和复合的命令（参看[[#Shell Commands|Shell Commands]]）。
# Performs the various shell expansions (see [[#Shell Expansions|Shell Expansions]]), breaking the expanded tokens into lists of filenames (see [[#Filename Expansion|Filename Expansion]]) and commands and arguments. 
#: 
# Performs any necessary redirections (see [[#Redirections|Redirections]]) and removes the redirection operators and their operands from the argument list. 
# Executes the command (see [[#Executing Commands|Executing Commands]]). 
# Optionally waits for the command to complete and collects its exit status (see [[#Exit Status|Exit Status]]).