Simple Pearl Question

skibud2 · 03-17-2005, 08:57 PM

I think it will be easier for me to show you all what I am trying to do rather than trying to explain it, so here it is:

echo "hello world" | perl -e 'print $ARGV';

Why does this not work. I have been looking all over the web for a reason, but I have not found much documentation pertaining to using perl from the command line. So web resources would be useful to me too.

Thanks,

Mike

Matir · 03-17-2005, 09:23 PM

Well, what are you trying to do? Count arguments? $#ARGV. Look at arguments? @ARGV. $ARGV is set to the input file when reading from <>. In the case above, you are not reading from any file.

puffinman · 03-18-2005, 02:56 AM

I think this is a good question and it involves several important concepts that are specific to perl. So what you're trying to do is print "hello world." The mistake in your code is that you are confusing piping some input to the program and giving arguments on the command line. Also you have some confusion over the use of @ARGV, and scalar/list context.

So, what I'll do is post several ways to do what you want. Please investigate them!

If you have any questions, please ask.

Code:

perl -e "print qq(hello world)"
echo "hello world" | perl -e "while (<>) { print }"
perl -e "print @ARGV" "hello world"
perl -e "$, = ' '; print @ARGV" hello world
perl -e "$, = ' '; print @ARGV" `echo "hello world"`

skibud2 · 03-18-2005, 07:24 AM

Puff -- Great answer. I will check out each method.

skibud2 · 03-18-2005, 07:29 AM

After browsing, is:

echo "hello world" | perl -e "while (<> ) { print }"

the same as

echo "hello world" | perl -e "while (<stdin> ) { print }"

It looks like it is, but I just want to confirm.

puffinman · 03-18-2005, 09:35 AM

Yes and no. From the camel book:

"When you read lines from <>, it magically gives you all the lines from all the files mentioned on the command line. If no files were mentioned, it gives you standard input instead, so your program is easy to insert into the middle of a pipeline of processes."