为什么这会导致无限循环?
#!/bin/bash
while [[ "$(ipcs | awk '{print $2}')" != "Semaphore" ]]; do
#Gonna get rid of the echo after working
echo "$(ipcs | awk '{print $2}')"
#I want to keep this
ipcrm shm "$(ipcs | awk '{print $2}')"
#I want this run after breaking out of the loop until I reach the string
#Message.
ipcrm -s "$(ipcs | awk '{print $2}')"
done
echo
exit 0
我已经验证我最终得到了 Semaphore,所以它应该跳出 while 循环。
$ echo $(ipcs | awk '{print $2}')
Shared shmid 262145 294914 2326531 Semaphore semid Message msqid
$ ipcs
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00000000 262145 bob 600 393216 2 dest
0x00000000 294914 bob 600 393216 2 dest
0x00000000 2490371 bob 600 998400 2 dest
------ Semaphore Arrays --------
key semid owner perms nsems
------ Message Queues --------
key msqid owner perms used-bytes messages
$ echo $(ipcs | awk '{print $1}')
------ key 0x00000000 0x00000000 0x00000000 ------ key ------ key
$ echo $(ipcs | awk '{print $2}')
Shared shmid 262145 294914 2490371 Semaphore semid Message msqid
答案1
$(ipcs | awk '{print $2}')
永远不等于Semaphore
.它总是等于:
Shared shmid 262145 294914 2326531 Semaphore semid Message msqid
你可能想要这样的东西:
for e in $(ipcs | awk '{print $2}'); do
[[ "$e" = "Semaphore" ]] && break
echo $e
done
echo
exit 0
您可能也喜欢这个awk
解决方案:
ipcs | awk '$2 == "Semaphore" {exit;} $2 != "" {print $2}'
一点解释:
- 如果第二个字段是信号, 出口。
- 否则,如果该字段不为空,则打印它。
以下是一些替代解决方案(假设我确实了解您的需求):
# List all shared memory segments keys
ipcs -m | awk 'NR > 3 && $1 != "" {print $1}'
# List all shared memory segments IDs
ipcs -m | awk 'NR > 3 && $2 != "" {print $2}'
对于每个示例,您都可以迭代结果:
for e in $(above command); do
echo $e
done
答案2
这是处理 while 循环的稍微不同的方法:
$ while read line; do
echo "$line";
if [[ "$line" != *Semaphore* ]]; then
echo "not semaphore";
else
echo "is semaphore";
fi;
done < <(ipcs | awk '{print $2}')
产生以下输出:
...
not semaphore
814972976
not semaphore
815005745
not semaphore
817070167
not semaphore
not semaphore
Semaphore
is semaphore
semid
not semaphore
请注意,当它到达字符串“Semaphore”时,它会正确识别它。