什么是bash中命令行参数的$ opt变量 [英] What is $opt variable for command line parameter in bash

问题描述

我有下面的bash脚本，我对$ opt的含义有些困惑.搜索后我没有找到有关它的详细信息.

I have below bash script, I am a bit confuse about what is $opt meaning. and I do not find detail information about it after search.

test.sh:

echo "opt:" $opt for opt; do echo $opt done

echo "opt:" $opt for opt; do echo $opt done

输出:
./test.sh -a -b c opt: -a -b c

output:
./test.sh -a -b c opt: -a -b c

推荐答案

来自 bash(1)手册页:

   for name [ [ in [ word ... ] ] ; ] do list ; done
          The list of words following in is expanded, generating a list of
          items.  The variable name is set to each element of this list in
          turn, and list is executed each time.  If the in word  is  omit‐
          ted,  the  for  command  executes  list once for each positional
          parameter that is set (see PARAMETERS below).  The return status
          is  the  exit  status of the last command that executes.  If the
          expansion of the items following in results in an empty list, no
          commands are executed, and the return status is 0.

因此，如果缺少in单词，则for循环将迭代脚本的位置参数，即$1，$2，$3，....

So, if the in word is missing the for loop iterates over the positional arguments to the script, i.e. $1, $2, $3, ....

名称opt没什么特别的，可以使用任何合法的变量名称.考虑一下此脚本及其输出:

There is nothing special about the name opt, any legal variable name can be used. Consider this script and its output:

#test.sh
echo $*    # output all positional parameters $1, $2,...
for x
do
    echo $x
done

$ ./test.sh -a -b hello
-a -b hello
-a
-b
hello

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