What is the difference btw "grep" and "egrep" ???

Posted on 2003-11-12
Medium Priority
Last Modified: 2008-01-09
What is the difference btw "grep" and "egrep" ???
Pls kindly elaborate if there's difference(s).
Thx =)
Question by:shchong2
LVL 45

Expert Comment

ID: 9730797
egrep stands for extended grep. You can do everything with egrep that you can do with grep. And it is probably somewhat better to use, but grep is a lot easier to remember.  The main difference is that you can use some extra symbols in egrep that let you search for strings in even fancier ways.

for more info ... refer to man pages
LVL 14

Expert Comment

ID: 9731911
Also, most modern grep implemenations actually do everything that egrep does if you use 'grep -E'

Expert Comment

ID: 9732530
Also too, egrep use a diferent way to manage the search for the regular expressions and so it resource needs are different from grep (you should be aware of that if you have very low resources or your search is particularily complex). It is supposed to let you make extensive use of reg-exps. but today common grep implementations give you enough power to use them extensively (it wasn't this way on the original implementations).

You should also check for 'fgrep' (fast-grep) which make it's searches based only on fixed-strings (no reg-exp) and is a lot faster than the other two if you just need to lookup for fixed strings.
Keep up with what's happening at Experts Exchange!

Sign up to receive Decoded, a new monthly digest with product updates, feature release info, continuing education opportunities, and more.

LVL 14

Expert Comment

ID: 9733273
Actually, grep, egrep, and fgrep are usually the same binary on most modern implemenations, and there are no performance or resource differences between them given the same search expression. In fact, egrep == 'grep -E' and fgrep == 'grep -F'

The only difference is the complexity of the search expressions they allow (simple string, simple regular expression, extended regular expression).

This wasn't true of early grep/egrep/fgrep implementations, but it is true for modern implementations.

Early implementations used different pattern matching algorithms that were optimized for different circumstances. But with the dicovery of the Boyer-Moore string-matching algorithm in the 1980's, there is no longer any need to use different algorithms as B-M is the optimum algorithm in all three situations.

Expert Comment

ID: 9742654
simply put, as from this man page entry...
Plain call with pattern
      grep [-E|-F] [-c|-l|-q] [-bhinsvwx] pattern [file ...]

    Call with (multiple) -e pattern
      grep [-E|-F] [-c|-l|-q] [-bhinsvwx] -e pattern...  [-e pattern] ...
           [file ...]
grep allows for a search of a single pattern/expression from a file.
egrep (grep -E) allows for multiple pattern search.

Accepted Solution

ChiefEngineer earned 80 total points
ID: 9742842
I'm affraid zile26 got confused with the case of the switches (remember Unix is case-sensitive).
His comment treat '-E' and '-e' as being the same when they're actually not:
'-E' stands for 'Extended' behavior while '-e' stands for 'expression pattern' to search for. That means that they serve different purposes and they can even be combined, as shown in the man page he posted here.

In short:

   grep <pattern>

  will search for <pattern> using simple regular expressions,

   grep -E <pattern>

  will search for <pattern> allowing use of Extended Regular Expressions,

  grep -e <pattern1> -e <pattern2> -e <pattern3>

  will search for any of <pattern1>, <pattern2> and <pattern3> using simple regular expressions, and finally

  grep -E -e <pattern1> -e <pattern2> -e <pattern3>

  will search for any of <pattern1>, <pattern2> and <pattern3> allowing use of Extended Regular Expressions.

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Let's say you need to move the data of a file system from one partition to another. This generally involves dismounting the file system, backing it up to tapes, and restoring it to a new partition. You may also copy the file system from one place to…
Java performance on Solaris - Managing CPUs There are various resource controls in operating system which directly/indirectly influence the performance of application. one of the most important resource controls is "CPU".   In a multithreaded…
This video shows how to set up a shell script to accept a positional parameter when called, pass that to a SQL script, accept the output from the statement back and then manipulate it in the Shell.
In a previous video, we went over how to export a DynamoDB table into Amazon S3.  In this video, we show how to load the export from S3 into a DynamoDB table.
Suggested Courses

587 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question