grep question, how to filter several type of patterns?

Question

I'm console newbie. As I know, matching multiple patterns like this:

aaa|bbb

But, | character is pipe on console, so how can I specify those multiple patterns for grep?

Answer 1

You can escape the pipe and put the pattern in quotes:

grep "aaa\|bbb"

or use -E:

grep -E "aaa|bbb"

or

grep -E aaa\|bbb

Answer 2

Put "" between your pattern, like egrep "toto|name"

Answer 3

Or you go

grep -ie aaa -ie bbb filename

to grep for aaa or bbb in filename, case insensitively.

Answer 4

Lastly, you can put your patterns into a file, and use the -f flag. So grep -f patternlist.txt files. Where patternlist.txt is simply:

aaa
bbb

Make sure there are no empty lines, though.

--Christopher Karel

Answer 5

Enclose your pattern in single quotes:

grep -E 'aaa|bbb'

Should your pattern include an apostrophe, enclose it in double quotes:

grep -E "its|it's"

If it contains both single and double quotes, enclose it in double quotes and prefix with a backslash the characters ", $, ` and \:

grep -E "its|it's|letter \"e\"|pay \$20|\`a'|C:\\\\AUTOEXEC\\.BAT"

The final example of C:\AUTOEXEC.BAT takes into account that backslash is special both to the shell and to the regular expression syntax of egrep.

PS: The bash quoting page is a must-read.

Answer 6

egrep "aaa|bbb|ccc" <file>

will find all rows with either aaa OR bbb OR ccc in the file

egrep -i "aaa|bbb|ccc" <file>

will find aaa OR aaA OR aAa OR Aaa OR aAA OR AAa OR AAA OR ... and the same for every other string enumerated between the pipe | characters.