Question

这就是我要做的事情：

我想创建一个可以使用counter_use in或counter_use out调用的脚本。如果我输入in我希望计数器在名为“counter”的文件中为数字值添加+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，我还希望输出Not logged in。

如果我将计数器硬编码为特定数字，则最后一部分是runnig。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，但代码可以简化以成为更惯用的（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声明更简洁地处理多个条件。
使用>&2

stderr

使用perl命令更新档案counter：
- -i激活就地更新
- -ple自动p提示（已修改）输入行，-l添加智能换行符，-e指定e xpression（脚本） run（以下参数）
- ++$_ / --$_然后简单地递增/递减手头的输入行（$_），这要感谢-p，自动输出，并且，由于-i，写回原始文件（松散地说;创建一个替换原始文件的新文件）。
使用算术评估（(( ... ))）来测试数字。

Answer 2

第一个问题是使用read命令。试试这个

read -p "in or out ?" input

-p选项用于指定要打印到stdout的内容
input是将存储用户输入的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in表达式测试输入是out还是if：

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

要向计数器文件中的值添加或减去1，您可以检索当前值内部文件，添加或减去1并写入新值内部文件（我不确定您是否要写入新值。请尝试以下操作：

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

必须存在计数器文件，因此您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

小心，用户输入必须是in或out（区分大小写），并且必须为空。要保护空答案，请尝试if [ "x$input" == "xin" ] [...]

希望这个帮助

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

Bash脚本 - 从文件

3 个答案: