Avoiding external utilities Post: 303010809

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Top Forums Shell Programming and Scripting Avoiding external utilities Post 303010809 by bakunin on Sunday 7th of January 2018 08:52:47 PM

01-07-2018

Registered User

Quote:

Originally Posted by SkySmart

nevertheless, here's what im trying to do to help me avoid external commands:

It is a good idea to avoid external utilities when possible, but that doesn't mean you should never use them. In fact they are quite good at what they are supposed to do and as long as you do not misuse them you are perfectly entitled to used them in your code.

In your case, where you search for a fixed string, you do not need egrepat all. egrep uses a very mighty (and therefore resource-intensive) regex machine, but to search for a fixed string you don't need that. Use fgrep ("fast grep"), which does the same as egrep but with a very limited (and hence resource-saving) regexp machine.

What you want to do cannot be done in shell. Actually it can be done, but not economically. It would look similar to this:

Code:

echo ${LongText} | while read line ; do
     case line in
          *RegexpA*)
               echo $line
               ;;

          *RegexpB*)
               echo $line
               ;;

     esac
done

I expect that to work slower than using (any) grep, though. echo, btw., is a shell builtin, if you use bash.

I hope this helps.

bakunin

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gzgrep

GZGREP(1)						      General Commands Manual							 GZGREP(1)

NAME

       gzgrep, gzegrep, gzfgrep - search possibly compressed files for a regular expression

SYNOPSIS

       gzgrep [ grep_options ] [ -e ] pattern filename...

DESCRIPTION

       gzgrep is used to invoke the grep on compress'ed or gzip'ed files. All options specified are passed directly to grep.  If no file is speci-
       fied, then the standard input is decompressed if necessary and fed to grep.  Otherwise the given files are uncompressed	if  necessary  and
       fed to grep.

       If  gzgrep  is  invoked as gzegrep or gzfgrep then egrep or fgrep is used instead of grep.  If the GREP environment variable is set, gzgrep
       uses it as the grep program to be invoked. For example:

	   for sh:  GREP=fgrep	gzgrep string files
	   for csh: (setenv GREP fgrep; gzgrep string files)

AUTHOR

       Charles Levert (charles@comm.polymtl.ca)

SEE ALSO

       grep(1), egrep(1), fgrep(1), gzdiff(1), gzmore(1), gznew(1), gzforce(1), gzip(1), gzexe(1)

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +--------------------+-----------------+
       |  ATTRIBUTE TYPE    | ATTRIBUTE VALUE |
       +--------------------+-----------------+
       |Availability	    | SUNWgzip	      |
       +--------------------+-----------------+
       |Interface Stability | External	      |
       +--------------------+-----------------+
NOTES

       Source for gzip is available in the SUNWgzipS package.

																	 GZGREP(1)