bash shell 脚本中一行末尾的分号是多余的吗？
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Semicolons superfluous at the end of a line in shell scripts?
提问by Nagel
I have a shell script which contains the following:
我有一个包含以下内容的 shell 脚本：
case in
0 )
echo = 0;
OUTPUT=3;;
1 )
echo = 1;
OUTPUT=4;;
2 )
echo = 2;
OUTPUT=4;;
esac
HID=;
BUNCH=16;
LR=.008;
Are semicolonscompletely superfluous in the snippet above? And is there any reason for some people using double semicolons?
是分号完全是多余的在上面的代码片段？有些人使用双分号有什么理由吗？
It appears semicolons are only a separator, something you would use instead of a new line.
看来分号只是一个分隔符，您可以使用它来代替换行符。
回答by Ignacio Vazquez-Abrams
Single semicolons at the end of a line are superfluous, since the newline is also a command separator. casespecifically needs double semicolons at the end of the last command in each pattern block; see help casefor details.
行尾的单个分号是多余的，因为换行符也是命令分隔符。case在每个模式块中的最后一个命令的末尾特别需要双分号；help case详情请参阅。
回答by Micha? ?rajer
According to man bash:
根据man bash：
metacharacter A character that, when unquoted, separates words. One of the following: | & ; ( ) < > space tab control operator A token that performs a control function. It is one of the following symbols: || & && ; ;; ( ) | |& <newline>
metacharacter A character that, when unquoted, separates words. One of the following: | & ; ( ) < > space tab control operator A token that performs a control function. It is one of the following symbols: || & && ; ;; ( ) | |& <newline>
So, the ;can be metacharacter or control operator, while the ;;is always a control operator (in case command).
因此， the;可以是元字符或控制运算符，而 the;;始终是控制运算符（如果是命令）。
In your particular code, all ;at the end of line are not needed. The ;;is needed however.
在您的特定代码中，;不需要所有在行尾的代码。该;;然是必要的。
回答by DanielGKiel
回答by Amit Ganvir
@Opensourcebook-Amit
@Opensourcebook-Amit
newlines equivalent to single semicolon ;on terminal or in shell script.
相当于;终端或 shell 脚本中的单个分号的换行符 。
See the below examples:
请参阅以下示例：
On terminal:
在终端：
[root@server test]# ls;pwd;
On shell script:
在 shell 脚本中：
[root@server test]# cat test4.sh
echo "Current UserName:"
whoami
echo -e "\nCurrent Date:";date;
[root@server test]#
But I am not agree with the comment that &is equivalent to newline or single semicolon
但我不同意&相当于换行符或单个分号的评论
&is run commands in background also a command separator but not worked as semicolon or newline.
&在后台运行命令也是命令分隔符，但不能用作分号或换行符。
回答by I J
@Ignacio Vazquez-Abrams
@伊格纳西奥巴斯克斯-艾布拉姆斯
Actually this is not completely accurate, single semicolons at the end of a line are notsuperfluous and are definitely not the same thing as new lines.
其实这并不完全准确，行尾的单个分号并不是多余的，绝对不是换行。
From the Bash Reference Manual
Commands separated by a ‘;' are executed sequentially; the shell waits for each command to terminate in turn. The return status is the exit status of the last command executed.
以“;”分隔的命令 依次执行；shell 依次等待每个命令终止。返回状态是最后执行的命令的退出状态。
Commands that are separated by "new line" might beexecuted in parallel when commands separated by semicolon are alwaysexecuted sequentially
当以分号分隔的命令始终按顺序执行时，以“换行”分隔的命令可能会并行执行
