Using sed to print the lines starting with two different patterns

Question

我已经在使用以下sed命令来打印以某个单词（例如A）开头的行，但是，无法弄清楚如何使用此命令来打印以A或B开头的行。

sed -n '/A/p' 1.txt > 2.txt

Answer 1

Just add an alternative:

sed -n '/A\|B/p' 1.txt > 2.txt

Note that this does not only print lines starting with A or B, but lines containing A or B. To make it really match at the beginning of a line, you have to add the anchor ^ :

sed -n '/^A\|^B/p' 1.txt > 2.txt

which is equivalent to

sed '/^A\|^B/!d' 1.txt > 2.txt

which means "Delete lines that do not start with A or B".

Answer 2

这可能对您有用：

sed -n '/^[AB]/p' 1.txt > 2.txt