Another Q about piping Perl

[Elvis]

Hi,
Just for fun, I'd like to use perl instead of sed on the following line:

echo $HOME/Mail/* |sed 's/sent-mail //

So far, I've tried various things that leave me with no output or wrong output. E.g:

 echo $HOME/Mail/* | perl -e 'while (<STDIN>=~s/sent-mail//) { print "
+$_"}'

I've had a look at the Capturing input from pipe? node, but I'm still clueless. I've also used the s2p (sed2perl) program, but the output seems far from succint. I thought perl would be able to do the same task in as short a line as the sed command. Can it?

I'm very much a perl novice (initiate even), and would really appretiate your help.

Thank You.

[stefp]

The idiom to execute perl statements on and print the result of each line of a file is
perl -pe 'perl_statements' < file
or
some_command | perl -pe 'perl_statements'

each line is stored in $_ on which perl_statements act.

Here you want to print all the files in the $HOME/Mail directory. An all perl solution is:
   map{ -f  $_  and print "$_ " } <$ENV{HOME}/MAIL/*>

Some people consider using map on empty context is bad form. I don't. They would propose instead:   for(<$ENV{HOME}/MAIL/*>) {  -f  $_  and print "$_ " }
or
  -f  $_  and print "$_ " for  <$ENV{HOME}/MAIL/*>

TMTOWTDI

-- stefp

[Ovid]

stefp wrote:

Some people consider using map on empty context is bad form. I don't.

I think it depends on the context. If you're doing a short one-liner like that, it's not a big deal. In fact, if you're just writing a small "throw away" script that only gets used once or twice and you don't care about performance or memory, then it's not a big deal IMHO. However, if you're writing large applications, it pays to be rigorous. Creating a bunch of only to throw away the return value is a waste of resources and a for loop is preferable. Doing what you did to print all the files in the $HOME/MAIL/ directory:

    # print all files in the directory (an overblown and limited 'ls' 
+or 'dir'
    perl -e '-f $_ and print "$_ " for glob(shift)' ./*

Side note: since I tested that on a Windows box and it doesn't like single quotes on the command line and I hate using \" all the time to embed quotes, I wrote this:

    perl -e "-f $_ and print $_.$,.$/ for glob(shift)" ./*

No wonder people say Perl has too much punctuation :)

Cheers,
Ovid

Update: Hmm... seems I wasn't paying attention to blakem's post.

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[blakem]

I like map as much as the next guy (see the "extended" Location field on my homenode) but why not write the above map as:

-f $_ && print "$_ " for <$ENV{HOME}/MAIL/*>

-Blake

[tommyw]

Well, the error message about being unable to modify <HANDLE> might be considered a bit of a clue: grab the input, and modify it separately:

echo $HOME/Mail/* | perl -e 'while (<STDIN>) { s/sent-mail//; print "$
+_"}'

Or just use the -p option, and really make it look like your sed command:

echo $HOME/Mail/* | perl -p -e '/sent-mail//'

update:Whoops. Of course, the missing s before the substitution string was meant as an exercise for the reader ;) echo $HOME/Mail/* | perl -p -e 's/sent-mail//'

But personally, I'd stick with sed, if I've got the choice: it's less memory hungry for such simple tasks

[thatguy]

I am not sure if you are trying to exclude the sent-mail folder or what.. if you are just pulling out the phrase 'sent-mail' (which will pull it out of even recieved mail) then this will work:
echo $HOME/Mail/* | perl -e 'while(<>){$_=~ s/sent-mail//;if($_){print}}'

if you just want the received mail, then you are better off with this:

echo $HOME/Mail/received | perl -e 'print <>'
-p

[chazzz]

Here's my take on this...

perl -e "while(<>){s/sent-mail //;print;}"

Short and sweet :)

[tye]

Several replies mention "-pe" but the default behavior of 'sed' is actually best duplicated with "-ne": echo $HOME/Mail/* | perl -ne "print if s/sent-mail //"

        - tye (but my friends call me "Tye")

[Elvis]

Thanks for the excellent replies.

FWIW, I'm trying to exculde my sent-mail folder from the listing. It's to do with my .muttrc file.

I'm not too sure I understand the map function well, but it made interesting reading. Also in future, I'm going to have to take more notice of the perl --help output. :)

Thanks Again.