Shell Programming and Scripting

sorry scrutinizer,

I still don't get it.

What is then the role of <$1>

or what means \1 in your example?
is then $1 == "bla"?

In the grep that you used "$1" gets replace by whatever is in the shell variable "$1" and so if $1 happens to be "gnorky", then it will grep for:

Code:

egrep -i "(from|to)=<gnorky>" mail.log

Indeed \1 is then "bla". \1 is the back reference, the same as $1 in perl. \1 works too in perl in the replacement part of the substitute functions, BTW. But grep is not a programming language, and so you can only use it as part of a matching operation..

Ah, great!

Now I got it!

Thanks a lot for your patience

Sorry @Scrutinizer,

I didn't get this:-(

What does mean "\1" ?

Where is $1 and in which way does it aid in matching...?

\1 is a back reference (just like $1 is in perl), it is a reference to a previous expression between parentheses:

Code:

$ echo blagdfgdblb | grep -E '(bl.).*\1'
$ echo blagdfgdbla | grep -E '(bl.).*\1'
blagdfgdbla

The matched part in the parentheses is "bla" and so \1 becomes "bla", so the string to match becomes: bla.*bla. There is no match with the first string, but there is with the second string...

OK!

Now it's clear.

Thanks a lot!