I need to know the gateway of the localhost
I tried with a system command and with a IP routing table but nothing.
system("ipconfig | findstr /i "Gateway"")
I except the output was the gateway but I got Bareword found where operator expected at script.pl line 63, near ""ipconfig | findstr /i "Gateway"
(Missing operator before Gateway?)
String found where operator expected at script.pl line 63, near "Gateway"""
syntax error at script.pl line 63, near ""ipconfig | findstr /i "Gateway"
Execution of script.pl aborted due to compilation errors.
Intro
findstring is useless, as perl is a wonderfull grep engine...
Under Linux, I will do:
my $gw;
open my $ipr,"ip r|";
while (<$ipr>) {
$gw=$1 if /default.*via ([0-9.]+) /;
};
print $gw."\n";
As your question stand for ipconfig, I think something like
open my $ipr,"ipconfig /all|";
while (<$ipr>) {
$gw=$1 if /[dD].*faul?t.*: ([0-9.]+) *$/;
};
print $gw."\n";
Nota: Regex is a try based on fr.wikipedia and en.wikipedia. Feedback welcome!
Grouped
my $gw;
my $regex='default.*via ([0-9.]+) ';
my $cmd='ip r';
if ($^O =~ "MSWin") {
$regex='[dD].*faul?t.*: ([0-9.]+) *$';
$cmd='ipconfig /all'
};
open my $ipr,$cmd."|";
while (<$ipr>) {
$gw=$1 if /$regex/;
};
print $gw."\n";
This work under my Debian Linux. No idea if this could work under MSWin... Feedback welcome!
Or by using traceroute:
use Net::Traceroute;
$tr = Net::Traceroute->new(host => "8.8.8.8",max_ttl=>1);
print "Gateway: " . $tr->hop_query_host(1,0) . "\n";
I see no-one has actually explained what your problem is.
You cannot use plain double-quote characters inside a double-quoted string. If you think about it, it should be obvious that the first double-quote character inside a double-quoted string will be seen as the end of the string.
Your code is like this:
system("ipconfig | findstr /i "Gateway"")
This is seen as a double-quoted string ("ipconfig | findstr /i") followed by a bareword (Gateway) and another double-quoted string (an empty string - ""). This is never going to compile successfully.
The easiest fix is to change your double-quoted string to a single-quoted string:
system('ipconfig | findstr /i "Gateway"')
But, as others have pointed out, it seems like a very strange idea to use findstr when you have the whole power of Perl available.
Related
A perl beginner here. I have been working on some simple one-liners to find and replace text in a file. I read about escaping all special characters with \Q\E or quotemeta() but found this only works when interpolating a variable. For example when I try to replace the part containing special characters directly, it fails. But when I store it in a scalar first it works. Of course, if I escape all the special character in backslashes it also works.
$ echo 'One$~^Three' | perl -pe 's/\Q$~^\E/Two/'
One$~^Three
$ echo 'One$~^Three' | perl -pe '$Sub=q($~^); s/\Q$Sub\E/Two/'
OneTwoThree
$ echo 'One$~^Three' | perl -pe 's/\$\~\^/Two/'
OneTwoThree
Can anyone explain this behavior and also show if any alternative exists that can directly quote special characters without using backslashes?
Interpolation happens first, then \Q, \U, \u, \L and \l.
That means
"abc\Qdef$ghi!jkl\Emno"
is equivalent to
"abc" . quotemeta("def" . $ghi . "!jkl") . "mno"
So,
s/\Q$~^/Two/ # not ok quotemeta($~ . "^")
s/\Q$Sub/Two/ # ok
s/\$\~\^/Two/ # ok
s/\$\Q~^/Two/ # ok
Why is it that simply changing from enclosing my one-liner with ' instead of " affects the behavior of the code? The first line of code produces what is expected and the second line of code gives (to me!) an unexpected result, printing out an unexpected array reference.
$ echo "puke|1|2|3|puke2" | perl -lne 'chomp;#a=split(/\|/,$_);print $a[4];'
puke2
$ echo "puke|1|2|3|puke2" | perl -lne "chomp;#a=split(/\|/,$_);print $a[4];"
This is the Perl version:
$ perl -v
This is perl, v5.10.1 (*) built for x86_64-linux-thread-multi
ARRAY(0x1f79b98)
With double quotes you are letting the shell interpolate variables first.
As you can check, $_ and $a are unset in the subshell forked for pipe by the parent shell. See a comment on $_ below.
So the double-quoted version is effectively
echo "puke|1|2|3|puke2" | perl -lne 'chomp;#a=split(/\|/);print [4];'
what prints the arrayref [4].
A comment on the effects of having $_ exposed to Bash. Thanks to Borodin for bringing this up.
The $_ is one of a handful of special shell parameters in Bash. It contains the last argument of the previous command, or the pathname of what invoked the shell or commands (via _ environment variable). See the link for a full description.
However, here it is being interpreted in a subshell forked to run the perl command, its first. Apparently it is not even set, as seen with
echo hi; echo hi | echo $_
which prints an empty line (after first hi). The reason may be that the _ environment variable just isn't set for a subshell for a pipe, but I don't see why this would be the case. For example,
echo hi; (echo $_)
prints two lines with hi even though ( ) starts a subshell.
In any case, $_ in the given pipeline isn't set.
The split part is then split(/\|/), so via default split(/\|/, $_) -- with nothing to split. With -w added this indeed prints a warning for use of uninitialized $_.
Note that this behavior depends on the shell. The tcsh won't run this with double quotes at all. In ksh and zsh the last part of pipeline runs in the main shell, not a subshell, so $_ is there.
This is actual a shell topic, not a perl topic.
In shell:
Single quotes preserve the literal value of all of the characters they contain, including the $ and backslash. However, with double quotes, the $, backtick, and backslash characters have special meaning.
For example:
'\"' evaluates to \"
whereas
"\'" evaluates to just '
because with double quotes, the backslash gets a special meaning as the escape character.
I'm having an issue with some code and I'm wondering if anyone can assist.
Basically I'm trying to execute an isql query against a database and assign it to a scalar variable. The isql command makes use of the column seperator which is defined as the pipe symbol.
So I have it set-up as such:
my $command = "isql -S -U -s| -i";
my $isql_output = `$command`;
The isql command works in isolation but when issued as a backtick it stops at the pipe. I've tried concatenating the $command string using sub-strings, using single quotes and backslash escaping items such as -s\"\|\" to no avail. I've also tried using qx instead of backticks.
Unfortunately I'm currently using an older version of perl (v5.6.1) with limited scope for upgrade so I'm not sure if I can resolve this.
You have to quote the | in a way that the shell does not recognize it as a special character. Two ways:
Put the -s| into single quotes: '-s|'. Perl will leave single quotes inside double quoted strings alone and pass them to the shell unmodified.
Escape the | with two backslashes: -s\\|. Why two? The first one is seen by Perl telling it to pass the next character through unmodified. Therefore the shell sees -s\| and does something very similar: it sees the single \ and knows not to treat the next char, |, special.
The problem is that the command is being executed through a shell.
You can avoid this by passing the command and arguments in a list rather than a single string.
The backtick construct does not support that, so you would need to use the open() function instead.
I haven't tested the following code but it gives the idea:
my #command = (qw(isql -Sserver -Uuser -Ppassword -s| -w4096), '–i' . $file);
print join(' ', #command), "\n";
open(my $fh, '-|', #command)
or die "failed to run isql command: $#\n";
my #isql_output = <$fh>;
close($fh);
my $isql_output = $isql_output[0]; chomp($isql_output);
If you're working with a 15 year old version of Perl (which Oracle users tend to do) I'm not sure this will all be supported. For instance, you may need to write chop instead of chomp.
UPDATE: the problem is not the Perl version, but this construct not being supported on Windows, according to the documentation. This must be qualified: I use Perl on Cygwin and it works fine there, but I don't know whether you can use Cygwin.
Single quotes should work. Try to run test perl script:
my $cmd = "./test.sh -S -U -s '|' -i";
print `$cmd`;
With test.sh:
#!/bin/sh
echo $#
Output should be -S -U -s | -i
I have a Perl script which runs fine under Perl 5.005 on HPUX 11i v3 and that causes a small problem under Perl 5.10 on my Ubuntu 11.04 box.
It boils down to a line like:
open (CMD, "do something | grep -E 'sometext$' |");
(it's actually capturing ps -ef output to see if a process is running but I don't think that's important (a)).
Now this runs fine on the HPUX environment but, when I try it out under Ubuntu, I get:
sh: Syntax error: Unterminated quoted string
By inserting copious debug statements, I tracked it down to that offending line then started removing characters one-by-one until it stopped complaining. Luckily, $ was the first one I tried and it stopped giving me the error, so I then changed the line to:
open (CMD, "do something | grep -E 'sometext\$' |");
and it worked fine (under Linux anyway - I haven't tested that on HPUX since I don't have access to that machine today - if it does work, I'll just use that approach but I'd still like to know why it's a problem).
So it seems obvious that the $ is "swallowing" the closing single quote under my Linux environment but not apparently on the HPUX one.
My question is simply, why? Surely there weren't any massive changes between 5.005 and 5.10. Or is there some sort of configuration item I'm missing?
(a) But, if you know a better way to do this without external CPAN modules (ie, with just the baseline Perl 5.005 installation), I'd be happy to know about it.
$' is a special variable (see perldoc perlvar). 5.005 was many versions ago, so it's possible that something has changed in the regexp engine to make this variable different (although it appears to be in 5.005 also)
As for the better way, you could at least only run the 'ps -ef' in a pipeline and do the 'grep' in perl.
Use the following!!!
use strict;
use warnings;
You would have gotten
Use of uninitialized value $' in concatenation (.) or string
A sigil followed by any punctuation symbol (on a standard keyboard) is a variable in Perl, regardless of if it is defined or not. So in a double quoted string [$#][symbol] will always be read as one token and interpolated unless the sigil is escaped.
I have a feeling that the difference you are seeing has to do with different system shells rather than different versions of perl.
Consider your line:
open (CMD, "do something | grep -E 'sometext$' |");
When perl sees that, it will interpolate the empty $' variable into the double quoted string, so the string becomes:
open (CMD, "do something | grep -E 'sometext |");
At that point, your shell gets to process a line that looks like:
do something | grep -E 'sometext
And if it succeeds or fails will depend on the shell's rules regarding unterminated strings (some shells will complain loudly, others will automatically terminate the string at eof).
If you were using the warnings pragma in your script, you probably would have gotten a warning about interpolating an undefined variable.
A shorter and cleaner way to read in the output of ps would be:
my #lines = grep /sometext\$/, `ps -ef`;
Or using an explicit open:
my #lines = grep /sometext\$/, do {
open my $fh, '|-', 'ps -ef' or die $!;
<$fh>
};
Because $' is a special variable in recent versions of Perl.
From the official documentation (perlvar):
$':
The string following whatever was matched by the last successful
pattern match (not counting any matches hidden within a BLOCK or
eval() enclosed by the current BLOCK).
If there were no successful pattern matches, $' is empty and your statement essentially interpolates to
open (CMD, "do something | grep -E 'sometext |");
Escaping the dollar sign (the solution that works for you on Linux) should work on HPUX too.
I'm not sure when was this variable added, but I can confirm that it exists in Perl 5.8.5. What's New for Perl 5.005 mentions $' (not as a new feature), so I think it was already there before then.
You should probably use single-quotes rather than double quotes around the string since there is nothing in the string that should be interpolated:
open (CMD, q{do something | grep -E 'sometext$' |});
Better would be to use the 3-argument form of open with a lexical file handle:
open my $cmd, '-|', q{do something | grep -E 'sometext$'} or die 'a horrible death';
I don't have a good explanation for why $' is being recognized as the special variable in 5.10 and yet it was not in 5.005. That is unexpected.
Is there a really good reason you can't upgrade to something like 5.14.1? Even if you don't change the system-provided Perl, there's no obvious reason you can't install a recent version in some other location and use that for all your scripting work.
$' is a special variable.
If you want to avoid variable expansion, just use q():
open (CMD, q(do something | grep -E 'sometext$' |));
I'm trying to find where two variables are being concatenated in a directory of scripts, but when I try the following:
grep -lire "$DATA_PATH . $AWARDS_YEAR" *
I get "undefined variable" errors...
I thought I could escape the $s by using:
grep -lire "\$DATA_PATH . \$AWARDS_YEAR" *
But I get the same error - so, how do you grep for strings with $s in?
Tcsh is a little different about variables than the usual shells, and it's the default on FreeBSD.
So, just use single quotes, '$VAR', or escape the $ outside of the quotes: \$"VAR"
Put it in single quotes, with the escaping slash:
grep -lire '\$DATA_PATH . \$AWARDS_YEAR' *
Also note, that the dot (.) is a regex character. If you don't want it to be, escape it, too (or don't use the -e option).
Here's a nice reference with more general info.