reading unix command with open syntax error

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

Hello,
I am trying to read in a list of processes using open, but the syntax; which works on the commandline, does not work in my perl script.
Would appreciate some ideas on what's causing the errors below.
Thanks!

open (IN, "ps -aux | awk -F" " '{print $1,$2 }' |" )  || die("Can't op
+en IN");


String found where operator expected at prog1.pl line 71, near ""ps -a
+ux | awk -F" " '{print $1,$2}' |""
        (Missing operator before  " '{print $1,$2}' |"?)
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Re: reading unix command with open syntax error by chromatic (Archbishop) on Mar 17, 2009 at 03:51 UTC
That error message means that you have a string (specifically `" '{print $1,$2 }' \|"`) where a string shouldn't be. While you intended to write only one string for the piped open, you have two strings, thanks to the field separator passed to awk. This is a good use of an alternate quoting construct: `open my $IN, q!ps -aux \| awk -F" " '{print $1,$2 }' \|! or die "Can't open pipe";` [download] I switched to the non-interpolating form because you probably don't want to interpolate the regexp match variables `$1` and `$2` into your string there. Of course, you could skip the pipe to awk and process the result with Perl (split) will come in handy....	[reply] [d/l] [select]
Re^2: reading unix command with open syntax error by csarid (Sexton) on Mar 17, 2009 at 14:44 UTC
Thanks! You're right... It was easier to just let perl handle it in the split. Although I could not get the q! to work for some reason.. but would like to better understand how this works.. can you point me to some FAQs or documents? Thanks again!	[reply]
Re^3: reading unix command with open syntax error by chromatic (Archbishop) on Mar 17, 2009 at 19:07 UTC
See "Quote and Quote-like Operators" in perlop.	[reply]
Re: reading unix command with open syntax error by codeacrobat (Chaplain) on Mar 17, 2009 at 23:49 UTC
Why using the ugly awk-pipe in the first place? perl -e ' for (`ps aux`){ ($pid,$ppid) = (split/\s+/)[1,2]; print "$pid $ppid\n"} ' [download] `print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});`	[reply] [d/l] [select]