Bash - 删除所有以“P”开头的行
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Bash - remove all lines beginning with 'P'
提问by user2450099
I have a text file that's about 300KB in size. I want to remove all lines from this file that begin with the letter "P". This is what I've been using:
我有一个大约 300KB 的文本文件。我想从这个文件中删除所有以字母“P”开头的行。这是我一直在使用的：
> cat file.txt | egrep -v P*
That isn't outputting to console. I can use cat on the file without another other commands and it prints out fine. My final intention being to:
那不是输出到控制台。我可以在没有其他命令的情况下在文件上使用 cat 并且它打印得很好。我的最终目的是：
> cat file.txt | egrep -v P* > new.txt
No error appears, it just doesn't print anything out and if I run the 2nd command, new.txt is empty. I should say I'm running Windows 7 with Cygwin installed.
没有出现错误，它只是不打印任何内容，如果我运行第二个命令，则 new.txt 为空。我应该说我正在运行安装了 Cygwin 的 Windows 7。
回答by édouard Lopez
回答by Zulu
With awk:
使用 awk：
awk '!/^P/' file.txt
Explanation
解释
- The condition starts with an
!(negation), that negatesthe following pattern ;/^P/means "match all lines starting with a capitalP",
- So, the pattern is negated to "ignore lines starting with a capital
P". - Finally, it leverage
awk's behavior when{ … }(action block) is missing, that is to print the record validating the condition.
- 条件以
!(否定)开头，否定以下模式；/^P/意思是“匹配所有以大写开头的行P”，
- 因此，该模式被否定为“忽略以大写开头的行
P”。 - 最后，
awk当{ … }( action block) 丢失时，它会利用的行为，即打印验证条件的记录。
So, to rephrase, it ignores lines starting with a capital Pand print everything else.
因此，换言之，它会忽略以大写开头的行P并打印所有其他内容。
Note
笔记
sedis line oriented and awkcolumn oriented. For your case you should use the first one, see Edouard Lopez's reponse.
sed是面向行和awk面向列的。对于您的情况，您应该使用第一个，请参阅 Edouard Lopez 的回复。
回答by Grzegorz ?ur
Use start of line mark and quotes:
使用行首标记和引号：
cat file.txt | egrep -v '^P.*'
P*means P zero or more times so together with -vgives you no lines
P*意味着 P 零次或多次，所以连同-v给你没有线
^P.*means start of line, then P, and any char zero or more times
^P.*表示行首，然后是 P 和任何字符零次或多次
Quoting is needed to prevent shell expansion.
需要引用以防止外壳扩展。
This can be shortened to
这可以缩短为
egrep -v ^P file.txt
because .*is not needed, therefore quoting is not needed and egrepcan read data from file.
因为.*不需要，因此不需要引用并且egrep可以从文件中读取数据。
As we don't use extended regular expressions grepwill also work fine
由于我们不使用扩展的正则表达式grep也可以正常工作
grep -v ^P file.txt
Finally
最后
grep -v ^P file.txt > new.txt
回答by Prasanth
This works:
这有效：
cat file.txt | egrep -v -e '^P'
-eindicates expression.
-e表示表达。
回答by bartimar
Use sedwith inplace substitution (for GNU sed, will also for your cygwin)
sed与就地替换一起使用（对于 GNU sed，也将用于您的 cygwin）
sed -i '/^P/d' file.txt
BSD (Mac) sed
BSD (Mac) sed
sed -i '' '/^P/d' file.txt
