Bash 脚本 - 从文件中添加/减去 1

Question

这就是我想要做的：

我想制作一个脚本，我可以使用counter_use in 或counter_use out 调用它。如果我输入in，我想要一个计数器为名为“counter”的文件中的数值加1，如果我输入out，我想从文件中减去1。

如果计数器中的值等于或大于 1，我还希望脚本输出 Logged in，如果计数器等于 0，则输出 Not logged in。

如果我将计数器硬编码为特定数字，则最后一部分将运行。问题是第一部分。

echo "In or out?"

read input > counterFile

if grep -q "in" counterFile
    then //what should I do here so that it adds +1 to a file called 
counter?

elif grep -q "out" counterFile
    then //what should I do here so that it subtracts -1 to a file called 
counter?

if [ $counter -ge 1 ]
    then
        echo "Logged in"

elif [ $counter -eq 0 ]
    then
        echo "Not logged in"

else
        echo "Wrong input"

fi

Answer 1

romaric crailox's helpful answer 包含许多有用的指针，但可以将代码精简为更惯用的（Bash）解决方案：

#!/bin/bash

# Create the counter file on demand.
[[ -f counter ]] || echo 0 > counter

# Prompt until valid input is received.
while read -p 'In or out? ' input; do

  case $input in
    'in')
      # Update the counter file by incrementing the number it contains.
      perl -i -ple '++$_' counter
      break # valid input received, exit the loop
      ;;
    'out')
      # Update the counter file by decrementing the number it contains.
      perl -i -ple '--$_' counter
      break # valid input received, exit the loop
      ;;
    *)
      echo "Invalid input." >&2  # echo error to *stderr*
      # Stay in the loop to prompt again.
      ;;    
  esac

done

# Read the updated counter file and echo the implied status.
counter=$(< counter)
if (( counter >= 1 )); then
  echo 'Logged in.'
elif (( counter == 0 )); then
  echo 'Not logged in.'
else
  echo "Invalid state: counter is $counter" >&2
fi

注意：

• 使用case ... esac 比if ... elif ... fi 语句更简洁地处理多个条件。

• 使用>&2将错误消息输出到stderr

• 使用perl 命令更新文件counter：

  • -i 激活就地更新
  • -ple 自动 prints（修改后的）输入行，-l 添加智能换行处理，-e 指定要运行的 expression（脚本）（以下参数）
  • ++$_ / --$_ 然后简单地增加/减少手头的输入行（$_），感谢-p，自动获取输出，感谢-i，写回原始文件（松散地说；会创建一个新文件来替换原来的文件）。

• 使用算术评估 ((( ... ))) 来测试数字。

Answer 2

第一个问题是读取命令的使用。试试这个

read -p "in or out ?" input

• -p 选项是指定要打印到标准输出的内容
• input 是用于存储用户输入的 shell 脚本变量的名称

在此命令之后，输入变量将为in 或out。 然后您可以使用if 表达式测试输入是in 还是out：

if [ "$input" == "in" ] [...]

要在计数器文件中添加或减去 1，您可以在文件中检索当前值，添加或减去 1 并在文件中写入新值（我不确定您是否要写入新值。试试这个：

crt_val=$(cat ./counter)
new_val=$(( crt_val + 1 ))
echo $new_val > ./counter

计数器文件必须存在，所以你可以在脚本的开头添加，

if [ -e ./counter ] ; then echo "0" > ./counter ; fi

最后，代码可以是这样的：

# user entry
read -p "in or out ? " input

# initialize counter file
if [ ! -e ./counter ] ; then echo "0" > ./counter ; fi

# Doing what user entry ask to do
if [ "$input" == "in" ]
then
  echo "in"
  crt_val=$(cat ./counter)
  new_val=$(( crt_val + 1 ))
  echo $new_val > ./counter
elif [ "$input" == "out" ]
then
  echo "out"
  crt_val=$(cat ./counter)
  new_val=$(( crt_val - 1 ))
  echo $new_val > ./counter
else
  echo "Wrong input, try in or out"
  exit 1
fi

# Output
if [ $new_val -ge 1 ]
then
  echo "Logged in"
elif [ $new_val -eq 0 ]
then
  echo "Not logged in"
else
  echo "Wrong counter value"
fi

请注意，用户输入必须完全是 in 或 out（区分大小写），并且不能为空。为了保护空答案，请尝试if [ "x$input" == "xin" ] [...]

希望有帮助

Answer 3

#!/bin/bash


echo "In or out?"

read c <&0  # reads from stdin file descriptor &0 is stdin

if [[ $c == 'In' ]] || [[ $c == 'in' ]];  
then
counter=$(<counter.txt) # reads counter from file
let "counter = counter +1"  # increases variable
echo "$counter" > 'counter.txt' # write new value to file overwriting the old
elif [[ $c == 'Out' ]] || [[ $c == 'out' ]];
then
counter=$(<counter.txt) # reads from file
let "counter = counter -1"
#echo "$counter" > 'counter.txt'
else
echo "wrong input..."
fi

Write to file, but overwrite it if it exists

https://askubuntu.com/questions/385528/how-to-increment-a-variable-in-bash/706683

http://ryanstutorials.net/bash-scripting-tutorial/bash-if-statements.php