虽然文件不包含字符串 BASH
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While file doesn't contain string BASH
提问by Jacob Collins
I am making a script for my school, and I was wondering how I could check a file, and if the string isn't in the file, do a code, but if it is, continue, like this:
我正在为我的学校制作脚本，我想知道如何检查文件，如果该字符串不在文件中，请执行代码，但如果是，请继续，如下所示：
while [ -z $(cat File.txt | grep "string" ) ] #Checking if file doesn't contain string
do
echo "No matching string!, trying again" #If it doesn't, run this code
done
echo "String matched!" #If it does, run this code
回答by George Vasiliou
You can do something like:
您可以执行以下操作：
$ if grep "string" file;then echo "found";else echo "not found"
To do a loop :
做一个循环：
$ while ! grep "no" file;do echo "not found";sleep 2;done
$ echo "found"
But be carefull not to enter an infinite loop. string or file must be changed otherwise the loop has no meaning.
但注意不要进入无限循环。必须更改字符串或文件，否则循环没有意义。
Above if/while works based on the return status of the command and not on the result. if grep finds string in file will return 0 = success = true if grep does not find string will return 1 = not success = false
上面的 if/while 是基于命令的返回状态而不是结果来工作的。如果 grep 在文件中找到字符串将返回 0 = 成功 = true 如果 grep 未找到字符串将返回 1 = 不成功 = 假
By using ! we revert the "false" to "true" to keep the loop running since while loops on something as soon as it is true.
通过使用 ！我们将“假”恢复为“真”以保持循环运行，因为一旦它为真，while 就会在某些东西上循环。
A more conventional while loop would be similar to your code but without the useless use of cat and the extra pipe:
更传统的 while 循环与您的代码类似，但没有无用的使用 cat 和额外的管道：
$ while [ -z $(grep "no" a.txt) ];do echo "not found";sleep 2;done
$ echo "found"
回答by Roald Nefs
A simple if statement to test if a 'string' is not in file.txt:
一个简单的 if 语句来测试“字符串”是否不在file.txt：
#!/bin/bash
if ! grep -q string file.txt; then
echo "string not found in file!"
else
echo "string found in file!"
fi
The -qoption (--quiet, --silent) ensures output is not written to standard output.
的-q选项（--quiet，--silent）可确保输出不被写入到标准输出。
A simple while loop to test is a 'string' is not in file.txt:
要测试的简单 while 循环是“字符串”不在file.txt：
#!/bin/bash
while ! grep -q string file.txt; do
echo "string not found in file!"
done
echo "string found in file!"
Note:be aware of the possibility that the while loop may cause a infinite loop!
注意：注意while循环可能导致无限循环的可能性！
回答by JayRugMan
Another simple way is to just do the following:
另一种简单的方法是执行以下操作：
[[ -z $(grep string file.file) ]] && echo "not found" || echo "found"
&&means AND - or execute the following command if the previous is true
&&表示 AND - 如果前一个为真，则执行以下命令
||means OR - or execute if the previous is false
||表示或 - 或如果前一个为假则执行
[[ -z $(expansion) ]]means return trueif the expansion output is null
[[ -z $(expansion) ]]表示如果扩展输出为空则返回真
This line is much like a double negative, basically: "return trueif the string is not foundin file.file; then echo not foundif true, or foundif false"
这一行很像双重否定，基本上：“如果在 file.file 中找不到字符串，则返回true；如果为true，则回显未找到，如果为false，则找到”
Example:
例子：
bashPrompt:$ [[ -z $(grep stackOverflow scsi_reservations.sh) ]] && echo "not found" || echo "found"
not found
bashPrompt:$ [[ -z $(grep reservations scsi_reservations.sh) ]] && echo "not found" || echo "found"
found
