请尝试以下操作：

awk '
    /^\[/ {                                     # the line starts with "["
        if ($1 ~ /^\[task/) f = 1               # set flag for "[task" line
        else f = 0                              # otherwise reset the flag
    }
    f {print}                                   # if flag is set, print the line
' input_file > output_file

那么output_file将如下所示：

[task,line:111] first
                second
[task,line:444] first
                second
                third
[task,line:555] first

您可以使用此awk：

awk 'NF == 2 {isTask = ($1 ~ /^\[task/)} isTask' file

[task,line:111] first
                second
[task,line:444] first
                second
                third
[task,line:555] first

我会利用GNU AWK来完成这个任务，让file.txt内容

[task,line:111] first
                second
[demo,line:222] first
[test,line:333] first
[task,line:444] first
                second
                third
[task,line:555] first

然后

awk 'BEGIN{RS="[";ORS=""}/task/{print "[" $0}' file.txt

给出输出

[task,line:111] first
                second
[task,line:444] first
                second
                third
[task,line:555] first

说明：我告诉GNU AWK行分隔符（RS）是[和输出行分隔符（ORS）是空字符串，即行是[和[之间的东西，则对于在I print内具有task的每一行，其具有前置的[，因为ORS是空字符串，所以没有添加多余的换行符（所需的换行符已经在行中）。如果想了解更多关于RS或ORS的信息，请阅读8 Powerful Awk Built-in Variables – FS, OFS, RS, ORS, NR, NF, FILENAME, FNR

• （在gawk 4.2.1中测试）*