建议减少代码行数-Unix

Question

我正在尝试基于变量test_1.txt中可用的值来更新作为主文件test.txt内部内容的IN的文件许可权。下面的脚本将帮助根据我的要求修改内容。但是我需要减少代码行数。因此，您可以提出任何减少行数并实现相同输出的方法的建议。

代码

#!/bin/bash
IN=750
Input=test.txt
Char_one=$(echo $IN | cut -c 1)
Char_two=$(echo $IN | cut -c 2)
Char_three=$(echo $IN | cut -c 3)

if [[ "$Char_one" == "7" ]]; then 
 Char_one="rwx"
elif [[ "$Char_one" == "6" ]]; then 
 Char_one="rw-"
elif [[ "$Char_one" == "5" ]]; then 
 Char_one="r-x"
elif [[ "$Char_one" == "4" ]]; then 
 Char_one="r--"
elif [[ "$Char_one" == "3" ]]; then 
 Char_one="-wx"
elif [[ "$Char_one" == "2" ]]; then     
 Char_one="rwx"
elif [[ "$Char_one" == "1" ]]; then     
 Char_one="-w-"
elif [[ "$Char_one" == "0" ]]; then     
 Char_one="---"
fi

if [[ "$Char_two" == "7" ]]; then 
 Char_two="rwx"
elif [[ "$Char_two" == "6" ]]; then 
 Char_two="rw-"
elif [[ "$Char_two" == "5" ]]; then 
 Char_two="r-x"
elif [[ "$Char_two" == "4" ]]; then 
 Char_two="r--"
elif [[ "$Char_two" == "3" ]]; then 
 Char_two="-wx"
elif [[ "$Char_two" == "2" ]]; then     
 Char_two="rwx"
elif [[ "$Char_two" == "1" ]]; then     
 Char_two="-w-"
elif [[ "$Char_two" == "0" ]]; then     
 Char_two="---"
fi

if [[ "$Char_three" == "7" ]]; then 
 Char_three="rwx"
elif [[ "$Char_three" == "6" ]]; then 
 Char_three="rw-"
elif [[ "$Char_three" == "5" ]]; then 
 Char_three="r-x"
elif [[ "$Char_three" == "4" ]]; then 
 Char_three="r--"
elif [[ "$Char_three" == "3" ]]; then 
 Char_three="-wx"
elif [[ "$Char_three" == "2" ]]; then   
 Char_three="rwx"
elif [[ "$Char_three" == "1" ]]; then   
 Char_three="-w-"
elif [[ "$Char_three" == "0" ]]; then   
 Char_three="---"
fi  

while IFS= read -r line;
  do
  j=1
  perm_1=$(echo $line | awk '{print $1}' | cut -c 2-4)
  perm_2=$(echo $line | awk '{print $1}' | cut -c 5-7)
  perm_3=$(echo $line | awk '{print $1}' | cut -c 8-10)   
  Def_Chmod=$(echo "$line" | sed -i "$j s/$perm_1$perm_2$perm_3/$Char_one$Char_two$Char_three/;" "$Input")                
    j=$((j+1))
  done <"$Input"

test.txt

-rwxrwxr-x test_1.txt

输出

执行上述代码后test.txt文件的内容。

-rwxr-x--- test_1.txt

Answer 1

请您尝试以下操作：

IN=750
Input=test.txt

str="-rwxrwxrwx"                        # start with the full permissions
for (( i=0; i<${#str}; i++ )); do       # loop from LSB to MSB
    j=$(( 1<<i ))                       # j changes as 1, 2, 4, 8 ...
    if (( ( 8#$IN & j ) == 0 )); then   # the bit is "off"
        str=${str:0:9-i}"-"${str:10-i:i}
                                        # then replace the position with "-"
    fi
done
# echo "$str"                           # just for debugging

sed -i "s/^[-rwx]\{10\}/$str/" "$Input" # update the permission string

然后test.txt将被修改为：

-rwxr-x--- test_1.txt

• 首先定义一个具有完全权限的变量str。
• 然后逐位检查从LSB到MSB的变量IN。
• 如果IN的位片为0，则将相关标志替换为破折号-。
• 最后用计算出的字符串修改文件Input。

请注意，您无需创建while循环即可读取逐行输入文件。 Sed将为您进行迭代。