Bash - remove all lines beginning with 'P'

Question

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:

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Answer 1

Use start of line mark and quotes:

 cat file.txt | egrep -v '^P.*'

P* means P zero or more times so together with -v gives you no lines

^P.* means start of line, then P, and any char zero or more times

Quoting is needed to prevent shell expansion.

This can be shortened to

egrep -v ^P file.txt

because .* is not needed, therefore quoting is not needed and egrep can read data from file.

As we don't use extended regular expressions grep will also work fine

grep -v ^P file.txt

Finally

grep -v ^P file.txt > new.txt