本文介绍了Bash变量串联在循环内失败的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
给出以下语句:
ac_reg_ids="-1" #Starting value
(mysql) | while read ac_reg_id; do
echo "$ac_reg_id" #variable is a result of a mysql query. Echoes a number.
ac_reg_ids="$ac_reg_ids, $ac_reg_id" #concatenate a comma and $ac_reg_id, fails.
done
echo "ac_reg_ids: $ac_reg_ids" #echoes -1
现在根据此答案:
串联应该起作用。为什么不呢?循环中有什么不同?
Concatenation should work. Why doesn't it, though? What's different within the loop?
以防万一:
更新
设置了-eux的输出:
Update
Output with set -eux:
+ echo 142
142
+ ac_reg_ids='-1, 142'
+ read ac_reg_id
推荐答案
类似于会指出,您正在修改子外壳中的ac_reg_id。
Like shellcheck would helpfully have pointed out, you're modifying ac_reg_ids in a subshell.
重写它以避免子shell:
Rewrite it to avoid the subshell:
ac_reg_ids="-1" #Starting value
while read ac_reg_id; do
echo "$ac_reg_id"
ac_reg_ids="$ac_reg_ids, $ac_reg_id"
done < <( mysql whatever ) # Redirect from process substution, avoiding pipeline
echo "ac_reg_ids: $ac_reg_ids"
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