Question

在以下脚本中，在将文件分配给名为＆＃39; byteNuevo＆＃39;的变量后，我得到文件的大小（以字节为单位）。然后进行比较，如果＆＃39; byteAnterior＆＃39;＆gt; 0减去＆＃39; byteNuevo - byteAnterior＆＃39;否则赋值为0.

问题在于＆＃39; byteAnterior＆＃39;没有价值，如果你之前的价值是“my_text.txt”，并希望我解释过这个脚本的作用是显示它之前的价值＆＃39; my_text.txt＆＃39;那现在......

我的例子：

    echo -e "\n- Starting 1.sh script--\n"

if [[ ! -f my_text.txt ]]; then > my_text.txt; fi

byteOLD="$(cat somefile.storing.byteOLD.value.txt)"
echo "-- OK: so far byteOLD is: $byteOLD";

byteModified=$(stat -c'%s' my_text.txt)

echo "-- Now after modifying my_text.txt on the fly, bytes in variable byteModified are: $byteModified";

((byteDiferencia = (byteOLD > 0) ? byteModified - byteOLD : 0))
echo "  -- byteDiferencia is set to = '$byteDiferencia'"

Answer 1

看看这有帮助吗？

案例1-我正在检查byteAnterior永远不会小于0 -OR我将错误地输出消息。

[jenkins@giga_akssb12 tomcat]$ cat 1.sh ; cat my_text.txt; ./1.sh ;
#!/bin/bash

echo -e "\n- Starting 1.sh script--\n"
#As you didn't mention how u r setting byteAnterior, im assuming user will pass a parameter to this script.
byteAnterior="$1"
if [[ $byteAnterior -lt 0 || -z "$byteAnterior" ]]; then echo -e "\n   -- Pass parameter value >= 0.\n"; exit 111; fi

byteNuevo=$(stat -c'%s' my_text.txt)
echo "-- byteAnterior : $byteAnterior"
echo "-- byteNuevo    : $byteNuevo"
echo

#Ternary operator use
((byteDiferencia = (byteAnterior > 0) ? byteNuevo - byteAnterior : 0))

echo "  -- byteDiferencia is set to = '$byteDiferencia'"
Hi shenzi.

ed?

- Starting 1.sh script--


   -- Pass parameter value >= 0.

[jenkins@giga_akssb12 tomcat]$
[jenkins@giga_akssb12 tomcat]$ ./1.sh 0;
- Starting 1.sh script--

-- byteAnterior : 0
-- byteNuevo    : 16

  -- byteDiferencia is set to = '0'
[jenkins@giga_akssb12 tomcat]$
[jenkins@giga_akssb12 tomcat]$
[jenkins@giga_akssb12 tomcat]$ ./1.sh 12;
- Starting 1.sh script--

-- byteAnterior : 12
-- byteNuevo    : 16

  -- byteDiferencia is set to = '4'
[jenkins@giga_akssb12 tomcat]$

情况2.如果你想将byteAnterior设置为0或小于0的东西或除了＆gt; = 1之外的有效数字以外的任何东西。然后COMMENT out check（if语句），现在byteDifferntia将被设置为0三元运算符。运行1.sh并传递-1作为第一个参数，你会看到：

#!/bin/bash

echo -e "\n- Starting 1.sh script--\n"
#As you didn't mention how u r setting byteAnterior, im assuming user will pass a parameter to this script.
byteAnterior="$1"
#if [[ $byteAnterior -lt 0 || -z "$byteAnterior" ]]; then echo -e "\n   -- Pass parameter value >= 0.\n"; exit 111; fi

byteNuevo=$(stat -c'%s' my_text.txt)
echo "-- byteAnterior : $byteAnterior"
echo "-- byteNuevo    : $byteNuevo"
echo

#Ternary operator use
((byteDiferencia = (byteAnterior > 0) ? byteNuevo - byteAnterior : 0))

echo "  -- byteDiferencia is set to = '$byteDiferencia'"
Hi shenzi.

ed?

- Starting 1.sh script--

-- byteAnterior : -1
-- byteNuevo    : 16

  -- byteDiferencia is set to = '0'

Answer 2

[giga@aks tomcat]$ rm my_text.txt

[giga@aks tomcat]$ ls -l my_text.txt
ls: my_text.txt: No such file or directory

[giga@aks tomcat]$
[giga@aks tomcat]$ cat 1.sh
#!/bin/bash

echo -e "\n- Starting 1.sh script--\n"

## Create a blank file if it doesn't exist.
## This will make byteOLD to hold 0 value. In future runs, it'll be append instead of overwriting.
if [[ ! -f my_text.txt ]]; then > my_text.txt; fi

byteOLD=$(stat -c'%s' my_text.txt)
echo "-- OK: so far byteOLD is: $byteOLD";

## Add something to the file in append mode >>.
## This will make byte2 to hold how much bytes you put there including last time if file exists.
echo -e "\n1\n2\n3\n4\n5\n6\n7\n8\n9\10\n11111111\n22222222222\n" >> my_text.txt
byteModified=$(stat -c'%s' my_text.txt)

echo "-- Now after modifying my_text.txt on the fly, bytes in variable byteModified are: $byteModified";

#Ternary operator use
((byteDiferencia = (byteOLD > 0) ? byteModified - byteOLD : 0))
echo "  -- byteDiferencia is set to = '$byteDiferencia'"

[giga@aks tomcat]$


[giga@aks tomcat]$ ./1.sh

- Starting 1.sh script--

-- OK: so far byteOLD is: 0
-- Now after modifying my_text.txt on the fly, bytes in variable byteModified are: 44
  -- byteDiferencia is set to = '0'
[giga@aks tomcat]$
[giga@aks tomcat]$ ls -l my_text.txt
-rw-r--r-- 1 jenkins dmadmin 44 Jun 12 15:17 my_text.txt
[giga@aks tomcat]$
[giga@aks tomcat]$ ./1.sh

- Starting 1.sh script--

-- OK: so far byteOLD is: 44
-- Now after modifying my_text.txt on the fly, bytes in variable byteModified are: 88
  -- byteDiferencia is set to = '44'
[giga@aks tomcat]$
[giga@aks tomcat]$ ls -l my_text.txt
-rw-r--r-- 1 jenkins dmadmin 88 Jun 12 15:17 my_text.txt
[giga@aks tomcat]$
[giga@aks tomcat]$
[giga@aks tomcat]$ ./1.sh

- Starting 1.sh script--

-- OK: so far byteOLD is: 88
-- Now after modifying my_text.txt on the fly, bytes in variable byteModified are: 132
  -- byteDiferencia is set to = '44'
[giga@aks tomcat]$

shell类型会话中的变量

2 个答案: