如何使用bash将文件中的行数写入单独文件中的行

我想计算一个文件中的行数，然后用行数覆盖第二个文件中的数字。例如

file1.txt

Apples
Oranges
Bananas

num_lines_in_file_1 = 100

num_lines_in_file_1 = 3

file2.txt

Apples
Oranges
Bananas

num_lines_in_file_1 = 100

num_lines_in_file_1 = 3

所以我需要把100换成3

file2.txt

Apples
Oranges
Bananas

num_lines_in_file_1 = 100

num_lines_in_file_1 = 3

我看到

wc-lfile1.txt

命令可以告诉我行数。我知道我可以使用

sed

替换一行，例如

sed -i "s/num_lines_in_file_1 = 100/num_lines_in_file_1 = 3/" file2.txt

---

但是，我不明白您如何将wc命令导入sed？它会发生在正则表达式内部吗？

使用命令替换：

sed -i "s/num_lines_in_file_1 = 100/num_lines_in_file_1 = $(wc -l < file1.txt)/" file2.txt

sed-i“s/num\u lines\u in_file\u 1=100/num\u lines\u in_file\u 1=$（wc-l

您也不需要重复整个短语，sed可以帮您记住：

sed -i "s/\(num_lines_in_file_1 = \)100/\1$(wc -l < file1.txt)/" file2.txt

sed-i“s/\（num\u lines\u in\u file\u 1=\）100/\1$（wc-l

使用命令替换：

sed -i "s/num_lines_in_file_1 = 100/num_lines_in_file_1 = $(wc -l < file1.txt)/" file2.txt

sed-i“s/num\u lines\u in_file\u 1=100/num\u lines\u in_file\u 1=$（wc-l

您也不需要重复整个短语，sed可以帮您记住：

sed -i "s/\(num_lines_in_file_1 = \)100/\1$(wc -l < file1.txt)/" file2.txt

sed-i“s/\（num\u lines\u in\u file\u 1=\）100/\1$（wc-l