Hi!
i'm reading the book Linux:The Textbook by Syed Sarwar.Following the examples on the book, i tried the grep/egrep command using bash on my Fedora8, and then encountered some problems.
all the grep/egrep commands below are used to search the text file students, whose content is:

$cat students
John Johnsen john.johnsen@tp.com 503.555.1111
Hassaan Sarwar hsarwar@k12.st.or 503.444.2132
David Kendall d_kendall@msnbc.org 229.111.2013
John Johnsen jjohnsen@psu.net 301.999.8888
Kelly Kimberly kellyk@umich.gov 555.123.9999
Maham Sarwar msarwark@k12.st.or 713.888.0000
Jamie Davidson j.davidson@uet.edu 515.001.2932
Nabeel Sarwar nsarwar@xyz.net 434.555.1212

OK! question #1:
should all regular expressions be quoted using '' or ""?
if i type $grep ^[A-H] students, does it simply go through the file to see if there is a line containing string "^[A-H]", rather than treat it as a regular expression?

question #2:
if the answer to #1 is yes, do '' and "" mean the same to each other?

question #3:
look at the result:

$grep '[a-z]\{4\}' students
John Johnsen john.johnsen@tp.com 503.555.1111
Hassaan Sarwar hsarwar@k12.st.or 503.444.2132
David Kendall d_kendall@msnbc.org 229.111.2013
John Johnsen jjohnsen@psu.net 301.999.8888
Kelly Kimberly kellyk@umich.gov 555.123.9999
Maham Sarwar msarwark@k12.st.or 713.888.0000
Jamie Davidson j.davidson@uet.edu 515.001.2932
Nabeel Sarwar nsarwar@xyz.net 434.555.1212

why are all of the lines printed out? i thought the command means only to print those lines containing exactly 4 lowercase letters consecutively. that's what {n} means according to manual page GREP(1).

question #4:
again the command $grep -n '[a-z]\{4\}' students
why are there backslashes?
i executed $grep -n '[a-z]{4}' students and saw nothing.
i checked manual page GREP(1),which says: in basic regular expressions the metacharacters ?, +, {, |, (, and ) lose their special meaning;instead use the backslashed versions \?, \+, \{, \|, \(, and \).
so does that mean my grep only support basic regular expression?however, GREP(1) also says: grep understands two different versions of regular expression syntax: "basic” and "extended.” In GNU grep, there is no difference in available functionality using either syntax.In other implementations, basic regular expressions are less powerful.so it seems that my grep is not a GNU grep,but some kind of other implementation.
is that correct?if so, what implementation is my grep? and what is GNU grep anyway?

thanks!

Please post your thread in only one forum. Posting a single thread in the most relevant forum will make it easier for members to help you and will keep the discussion in one place. This thread is being closed because it is a duplicate.