bash bash中while循环的布尔类型？
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boolean type for while loop in bash?
提问by user151841
I have a cron script on a shared web host that occasionally gets killed. I'd like to make a loop in bash that tries again if it gets killed, because most of the time it will make it. I'm having trouble with the syntax for storing a boolean value :P
我在共享网络主机上有一个 cron 脚本，它偶尔会被杀死。我想在 bash 中创建一个循环，如果它被杀死，它会再次尝试，因为大多数时候它都会成功。我在存储布尔值的语法方面遇到问题：P
#!/bin/bash
VAR=0;
while [ $VAR ]; do
if nice -19 mysqldump -uuser -ppassword -h database.hostname.com --skip-opt --all --complete-insert --add-drop-table database_name > ~/file/system/path/filename.sql; then
VAR=1;
fi
done
So the script recovers from a killed process okay, but once it's run properly, the new VARvalue doesn't kill the whileloop.
所以脚本可以从一个被杀死的进程中恢复，但是一旦它正常运行，新VAR值就不会终止while循环。
What am I doing wrong?
我究竟做错了什么？
采纳答案by kennytm
Try
尝试
while [ "$VAR" -eq 0 ]; do
0and 1are both considered True because they are not null strings.
0和1都被认为是 True 因为它们不是空字符串。
回答by Jürgen H?tzel
No need to you a helper variable, consider using:
不需要你的辅助变量，考虑使用：
while ! mysqldump .....; do :;done
回答by amertune
You could use /bin/trueand /bin/false. Although while ! mysqldump .....; do :;done(Jürgen H?tzel's solution) would be better in this case, there are other cases when using trueand falseare useful.
你可以使用/bin/true和/bin/false。虽然while ! mysqldump .....; do :;done（Jürgen H?tzel 的解决方案）在这种情况下会更好，但在使用时还有其他情况true并且false很有用。
#!/bin/bash
VAR=true
while $VAR; do
if nice -19 mysqldump -uuser -ppassword -h database.hostname.com --skip-opt --all --complete-insert --add-drop-table database_name > ~/file/system/path/filename.sql; then
VAR=false
fi
done
回答by Paused until further notice.
In Bash, you can do a numeric conditional using double parentheses rather than a string conditional, but the logic is inverted:
在 Bash 中，您可以使用双括号而不是字符串条件来执行数字条件，但逻辑是颠倒的：
#!/bin/bash
VAR=1;
while (( VAR )); do
if nice -19 mysqldump -uuser -ppassword -h database.hostname.com --skip-opt --all --complete-insert --add-drop-table database_name > ~/file/system/path/filename.sql; then
VAR=0;
fi
done
回答by Rondo
I like 'until' better for this... :
我喜欢“直到”更好...：
i=0
until [ $_done ]; do
echo stuff...;
sleep 1;
(( i++ ));
if [ "$i" -gt 9 ]; then
_done=1
fi
done
i=0
until [ $_done ]; do
echo stuff...;
sleep 1;
(( i++ ));
if [ "$i" -gt 9 ]; then
_done=1
fi
done
