SHELL脚本编程条件选择(if语句)和条件判断(case语句)

　　　　　　　　　　　　　　　　SHELL脚本编程条件选择(if语句)和条件判断(case语句)

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　作者：尹正杰

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一.条件选择if语句

[root@node101.yinzhengjie.org.cn ~]# help if
if: if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else COMMANDS; ] fi
    Execute commands based on conditional.
    
    The `if COMMANDS' list is executed.  If its exit status is zero, then the
    `then COMMANDS' list is executed.  Otherwise, each `elif COMMANDS' list is
    executed in turn, and if its exit status is zero, the corresponding
    `then COMMANDS' list is executed and the if command completes.  Otherwise,
    the `else COMMANDS' list is executed, if present.  The exit status of the
    entire construct is the exit status of the last command executed, or zero
    if no condition tested true.
    
    Exit Status:
    Returns the status of the last command executed.
[root@node101.yinzhengjie.org.cn ~]# 
[root@node101.yinzhengjie.org.cn ~]# 

[root@node101.yinzhengjie.org.cn ~]# help if　　　　　　　　#查看if语句的帮助信息