Perl substitute with regex - perl

Question

When I run this command over a Perl one liner, it picks up the the regular expression -
so that can't be bad.
more tagcommands | perl -nle 'print /(\d{8}_\d{9})/' | sort
12012011_000005769
12012011_000005772
12162011_000005792
12162011_000005792
But when I run this script over the command invocation below, it does not pick up the
regex.
#!/usr/bin/perl
use strict;
my $switch="12012011_000005777";
open (FILE, "more /home/shortcasper/work/tagcommands|");
my #array_old = (<FILE>) ;
my #array_new = #array_old ;
foreach my $line(#array_new) {
$line =~ s/\d{8}_\d{9}/$switch/g;
print $line;
sleep 1;
}
This is the data that I am feeding into the script
/CASPERBOT/START URL=simplefile:///data/tag/squirrels/squirrels /12012011_000005777N.dart.gz CASPER=SeqRashMessage
/CASPERBOT/ADDSERVER simplefile:///data/tag/squirrels/12012011_0000057770.dart.trans.gz
/CASPERRIP/newApp multistitch CASPER_BIN
/CASPER_BIN/START URLS=simplefile:///data/tag/squirrels /12012011_000005777R.rash.gz?exitOnEOF=false;binaryfile:///data/tag/squirrels/12162011_000005792D.binaryBlob.gz?exitOnEOF=false;simplefile:///data/tag/squirrels/12012011_000005777E.bean.trans.gz?exitOnEOF=false EXTRACTORS=rash;island;rash BINARY=T

Answer 1

You should study your one-liner to see how it works. First check perl -h to learn about the switches used:
-l[octal] enable line ending processing, specifies line terminator
-n assume "while (<>) { ... }" loop around program
The first one is not exactly self-explanatory, but what -l actually does is chomp each line, and then change $\ and $/ to newline. So, your one-liner:
perl -nle 'print /(\d{8}_\d{9})/'
Actually does this:
$\ = "\n";
while (<>) {
chomp;
print /(\d{8}_\d{9})/;
}
A very easy way to see this is to use the Deparse command:
$ perl -MO=Deparse -nle 'print /(\d{8}_\d{9})/'
BEGIN { $/ = "\n"; $\ = "\n"; }
LINE: while (defined($_ = <ARGV>)) {
chomp $_;
print /(\d{8}_\d{9})/;
}
-e syntax OK
So, that's how you transform that into a working script.
I have no idea how you went from that to this:
use strict;
my $switch="12012011_000005777";
open (FILE, "more /home/shortcasper/work/tagcommands|");
my #array_old = (<FILE>) ;
my #array_new = #array_old ;
foreach my $line(#array_new) {
$line =~ s/\d{8}_\d{9}/$switch/g;
print $line;
sleep 1;
}
First of all, why are you opening a pipe from the more command to read a text file? That is like calling a tow truck to fetch you a cab. Just open the file. Or better yet, don't. Just use the diamond operator, like you did the first time.
You don't need to first copy the lines of a file to an array, and then use the array. while(<FILE>) is a simple way to do it.
In your one-liner, you print the regex. Well, you print the return value of the regex. In this script, you print $line. I'm not sure how you thought that would do the same thing.
Your regex here will remove all set of numbers and replace it with the ones in your script. Nothing else.
You may also be aware that sleep 1 will not do what you think. Try this one-liner, for example:
perl -we 'for (1 .. 10) { print "line $_\n"; sleep 1; }'
As you will notice, it will simply wait 10 seconds then print everything at once. That's because perl by default prints to the standard output buffer (in the shell!), and that buffer is not printed until it is full or flushed (when the perl execution ends). So, it's a perception problem. Everything works like it should, you just don't see it.
If you absolutely want to have a sleep statement in your script, you'll probably want to autoflush, e.g. STDOUT->autoflush(1);
However, why are you doing that? Is it so you will have time to read the numbers? If so, put that more statement at the end of your one-liner instead:
perl ...... | more
That will pipe the output into the more command, so you can read it at your own pace. Now, for your one-liner:
Always also use -w, unless you specifically want to avoid getting warnings (which basically you never should).
Your one-liner will only print the first match. If you want to print all the matches on a new line:
perl -wnle 'print for /(\d{8}_\d{9})/g'
If you want to print all the matches, but keep the ones from the same line on the same line:
perl -wnle 'print "#a" if #a = /(\d{8}_\d{9})/g'
Well, that should cover it.

Answer 2

Your open call may be failing (you should always check the result of an open to make sure it succeeded if the rest of the program depends on it) but I believe your problem is in complicating things by opening a pipe from a more command instead of simply opening the file itself. Change the open to simply
open FILE, "/home/shortcasper/work/tagcommands" or die $!;
and things should improve.