Shell Programming and Scripting

Hope you are not confused with the usage of grep -E and grep -F. Also at any time, you can refer to the man grep

You still seem to be confused. The -F option to the grep utility has nothing to do with the | extended regular expression special character.

The grep utility searches input files for a list of fixed strings (with the -F option), extended regular expressions (with the -E option), or basic regular expressions (when neither -E nor -F are given). The list can be specified with separate -e options; by a single operand containing the list of expressions on separate lines; by using the -f option to name a file containing strings, BREs, or EREs on separate lines in the file; or by a combination of any or all of the above.

There weren't any BRE or ERE special characters in your sample list of strings to be matched. When that is the case, you can either use fixed strings on separate lines or as separate -e option arguments, or you can convert the fixed strings into an ERE using the | ERE special character to separate the strings in a single ERE. With a large file or with a lot of strings, fixed string searches are likely to be much faster ERE evaluations.

When you see something suggested in these forums that you don't understand, look at the man pages (as clx suggested). If you can't figure out why it worked after reading the man pages, ask us to explain it. We want to help you learn how to use the tools available on UNIX and Linux systems. Note that the utilities available vary from system to system and the options that are available on a given utility also vary from system to system, so when you pose a problem or ask a question, tell us what operating system including the version of that operating system and what shell you're using so we can explain things that will work in your environment.

As a Linux sysadmin, I usually read the man pages but it looks like this time I needed extra help.

Your explanation was very helpful, now I understand how it works.

To set some background about myself, long ago I've done some basic shell scripting with bash and then I had to quit for a few years to do more orientated sysadmin tasks. It's kind of frustrating when you realise that you forgot a lot of things. Now I want to catch up and expand my knowledge. I've also started learning about ksh, which is quite new to me.

Thanks a lot for your concern. I hope to be helpful as well.