help understanding regex with grep & sed

I recently had trouble with some regex on the command-line, and found that for matching a backslash, different numbers of characters can be used. This number depends on the quoting used for the regex (none, single quotes, double quotes).

I know through (my very limited) experience that you can't use the asterisk alone in a regex, but I still don't quite understand why. After all, it should match 'any or no characters'. To my mind, '*grep' should match:

grep egrep fgrep

While '.*grep' should match

egrep fgrep

...but not 'grep' because it seems like we are insisting upon a character in front of 'grep' with that dot.

I've seen several instances where people are doing this:

grep [f]oobar

But I don't understand why that is preferable to

grep foobar

Dear all My boss recomended me to update my script code like this.

Code: PIDFile=`cat pid` PIDMemory=`ps -ef | grep $PIDFile | grep -v grep` if [ $?

Hi

Here is the problem ( Exercise 3-3, Using The Shell of The Unix Programming Environment, Kerninghan, Pike, 3rd edition ):

Predict what each of the following grep commands will do, and then verify your understanding.

Code: grep \$ grep \\$ grep \\\$ grep '\$' grep '\'$' grep \\ grep \\\\ grep "\$" grep '"$' grep "$" A file containing these command

Of these two ways of searching a file recursively in all the subdirectories, which is faster / better ?

find . -regex ".*/.*abc.*"

or

find . | grep ".*abc.*"

Hello,

I have a file that I want to be able to insert a new line before every instance of a regex.

Hi,

I must be overlooking something, but I don't understand why this doesn't work. I'm trying to grep on a date, excluding all the lines starting with a dash:

testfile:

Code: #2013-12-31 2013-12-31 code:

Code: grep '^[^#]2013-12-31' testfile I'm expecting to see just the second line '2013-12-31' but I don't get any results. grep -v is not an option btw.

I am trying to understand the difference between grep -e and grep -E.