pure perl versus grep -v in unix

[gyandwivedi]

what should I use in perl /in place of grep -v in unix.

[numberwhun]

Well, that depends. You could learn how to use Perl Regular Expressions and get really creative, or you could use back tics and use `grep -v`. (that is what I would probably do it I didn't have time to mess with the regex)

Regards,

Jeff

[gyandwivedi]

hi Jeff ..thanks a lot for ur quick response I have tried it but still having issues.
This is how i m using this system("zcat $file | grep -i TYPE=ERROR | `grep -v` BackendResponse Exception > /tmp/err.2wd")

getting following on running

sh: BackendResponse Exception: not found
Usage: grep -hblcnsviw pattern file . . .

can anyone please suggest sth on this

[miller]

backticks are used in perl, but that string passed to the system command is a system level operation. Therefore don't use the backticks.

system("zcat $file  | grep -i TYPE=ERROR | grep -v BackendResponseException > /tmp/err.2wd")
 

Obviously try to get any system command to work at the command prompt first and then paste it into your perl code.

- Miller

[numberwhun]

backticks are used in perl, but that string passed to the system command is a system level operation. Therefore don't use the backticks.

Is that just a "best practices" thing? I ask only because the result should be the same, yes?

Regards,

Jeff

[KevinADC]

you should generally not use a function or operator that returns results, in a void context, like backtiks:

`command`; # backtiks used in void context

system() does not return results (it returns the exit value) from the program/application so is good for running commands that output results somewhere else, like a file. system() also does some "magical" things with the arguments passed to it. See the system() docs for details:

perldoc system()

[miller]

I'm sorry, I wasn't very clear.

All I meant to point out was that using backticks "inside" the system command was wrong. Using backticks instead of a system command would be just fine, and is in fact how the majority of coders I've observed tend to do such things.

- Miller

[KevinADC]

I'm sorry, I wasn't very clear.

All I meant to point out was that using backticks "inside" the system command was wrong. Using backticks instead of a system command would be just fine, and is in fact how the majority of coders I've observed tend to do such things.

- Miller

that was subtle, I missed it myself:

system("zcat $file | grep -i TYPE=ERROR | `grep -v` BackendResponse Exception > /tmp/err.2wd")

backtiks, literally, in the system command

[numberwhun]

that was subtle, I missed it myself:

system("zcat $file | grep -i TYPE=ERROR | `grep -v` BackendResponse Exception > /tmp/err.2wd")

backtiks, literally, in the system command

Oh, ok. I see now. I was curious because I knew that system returned a return code, but if you were doing something, system wise, that returned a value, then you almost HAVE to use backtics. (not to mention, if it was a bad practice, then I have been doing some very bad coding). :-)

Thanks for the clarification, both of you!!!

Regards,

Jeff

[numberwhun]

Kevin,

I sent you a PM.

Jeff