A step on the path to enlightenment

coolmichael has asked for the wisdom of the Perl Monks concerning the following question:

To quote an email I just wrote:

I'm quite fond of a command line interface directly to perl:
perl -e "print eval, \"\n\" while(<>);"
which would look nicer in a non-dos shell with better quoting possibilities. And it can be even shorter
perl -p -e "$_=eval"
but then you don't get new lines after each answer.
perl -p -e "s/(.*)/$1/ee"
also works very well, but is longer.

I've never understood s///e very well before, but this just occurred to me while I was writing it. And it worked. I was amazed.

The big question is, why does it work. I don't really know.

--
negativespace.net - all things inbetween.

Comment on A step on the path to enlightenment Select or Download Code

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Re: A step on the path to enlightenment by Chmrr (Vicar) on Mar 17, 2003 at 00:18 UTC
Each /e tacked onto the end is essentially doing another `eval`. The first `eval` evaluates `$1`, which gets it what was matched -- namely, the whole string. The second /e applies eval to what we just got -- the whole string. Thus, it evaluates whatever you typed. As a side note, you can have your cake and eat it two with your second option -- `perl -ple "$_=eval"` will give you your newline. perl -pe '"I lo`+$^X$\"$]!$/"=~m%(.)%s;$_=$1;y^`+*^e v^#$&V"+@( NO CARRIER'	[reply] [d/l] [select]
Re: A step on the path to enlightenment by grantm (Parson) on Mar 17, 2003 at 04:25 UTC
`perl -p -e "$_=eval"` but then you don't get new lines after each answer You could use -l to tack on the newlines: `perl -lpe "$_=eval"`	[reply] [d/l] [select]
Re: A step on the path to enlightenment by Aristotle (Chancellor) on Mar 17, 2003 at 12:58 UTC
And of course you can also use `-l` to shorten any other variants. `-n` might also be of interest. `perl -le "print eval while <>" perl -nle "print eval" perl -ple "$_=eval"` [download] Personally, simply for the sake of clarity, I'd prefer the `-n` variant. Makeshifts last the longest.	[reply] [d/l]


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