bash 使用 awk 将标题放入文本文件中
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Using awk to put a header in a text file
提问by JM88
I have lots of text files and need to put a header on each one of them depending of the data on each file.
我有很多文本文件，需要根据每个文件上的数据在每个文件上放置一个标题。
This awk command accomplishes the task:
这个 awk 命令完成了任务：
awk 'NR==1{first=}{sum+=;}END{last=;print NR,last,"L";}' my_text.file
But this prints it on the screen and I want to put this output in the header of each of my file, and saving the modifications with the same file name.
但这会将它打印在屏幕上，我想将此输出放在每个文件的标题中，并使用相同的文件名保存修改。
Here is what I've tried:
这是我尝试过的：
for i in *.txt
do
echo Processing ${i}
cat awk 'NR==1{first=}{sum+=;}END{last=;print NR,last,"L";}' "${i}" ${i} > $$.tmp && mv $$.tmp "${i}"
done
So I guess I can't use cat to put them as a header, or am I doing something wrong?
所以我想我不能用 cat 把它们作为标题，还是我做错了什么？
Thanks in advance
提前致谢
回答by MLSC
UPDATE:
更新：
with awk:
与awk：
awk 'BEGIN{print "header"}1' test.txt
without awk:
没有awk：
with cat& echo:
与cat& echo：
cat <(echo "header") test.txt
(OR)
（或者）
using tac:
使用tac：
tac test.txt | echo "header" >> test.txt | tac test.txt
回答by Ed Morton
I THINK what you're trying to do with your loop is:
我认为你试图用你的循环做的是：
for i in *.txt
do
echo "Processing $i"
awk 'NR==1{first=}{sum+=}END{last=;print NR,last,"L"}' "$i" > $$.tmp &&
cat "$i" >> $$.tmp &&
mv $$.tmp "$i"
done
but it's not clear what you're really trying to do since you never use firstor sumand setting lastin the END section is a bad idea as it will not work across all awks and there's a simple alternative.
但不清楚你真正想要做什么，因为你从不使用firstorsum并且last在 END 部分设置是一个坏主意，因为它不适用于所有 awk 并且有一个简单的替代方案。
If you update your question with some sample input and expected output we can help you.
如果您使用一些示例输入和预期输出更新您的问题，我们可以为您提供帮助。
