命令的含义是“不执行任何操作".在Bash中有条件吗? [英] What command means "do nothing" in a conditional in Bash?

问题描述

有时在进行条件查询时，我不需要代码执行任何操作，例如，在这里，我希望Bash在 $ a 大于"10"时不执行任何操作，如果 $ a 小于"5"，否则打印"2":

Sometimes when making conditionals, I need the code to do nothing, e.g., here, I want Bash to do nothing when $a is greater than "10", print "1" if $a is less than "5", otherwise, print "2":

if [ "$a" -ge 10 ]
then
elif [ "$a" -le 5 ]
then
    echo "1"
else
    echo "2"
fi

但这会导致错误.有没有什么不做的命令也不会减慢我的脚本的速度吗?

This makes an error though. Is there a command which will do nothing and also not slow down my script?

推荐答案

shell中的no-op命令是:(冒号).

The no-op command in shell is : (colon).

if [ "$a" -ge 10 ]
then
    :
elif [ "$a" -le 5 ]
then
    echo "1"
else
    echo "2"
fi

来自 bash手册:

:(冒号)
除了扩展参数和执行重定向之外，什么也不要做.返回状态为零.

: (a colon)
Do nothing beyond expanding arguments and performing redirections. The return status is zero.

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