system call and newline interpretattion.

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

Dear Monks, I need your esteemed wisdom.
I am trying to run an scp command on a ermote system which I am pretty sure is being split at the whitespace between the 2 arguments. I have tried every trick in my library to no avail. How do I avoid the command being split into 2 lines? The code is below:

$command = "scp $user\@$ip:$source/$_ $staging/$_";<br>
print("$command\n");<br>
system($command);<br>
[download]

and the output:

scp daylite_backup@192.168.0.53:/home/staging/dayliteLeads/courseBooki
+ngs/1116932421807.xml
<br> /dayliteImports/staging_courses/1116932421807.xml
<br>
usage: scp [-pqrvBC1246] [-F config] [-S program] [-P port]<br>
           [-c cipher] [-i identity] [-l limit] [-o option]<br>
           [[user@]host1:]file1 [...] [[user@]host2:]file2<br>
sh: line 2: /dayliteImports/staging_courses/1116932421807.xml: No such
+ file or directory
[download]

Janitored by holli - added code tags

Comment on system call and newline interpretattion. Select or Download Code

Replies are listed 'Best First'.
Re: system call and newline interpretattion. by Fletch (Bishop) on May 24, 2005 at 14:35 UTC
I'd check that `$_` doesn't already have a newline on the end (see `perldoc -f chomp`).	[reply] [d/l] [select]
Re: system call and newline interpretattion. by davidrw (Prior) on May 24, 2005 at 14:50 UTC
I think the consensus is clearly that $_ has a newline on it, but just wanted to add one other note -- system() can take the program and argument list as well: `chomp; my @args = ("$user\@$ip:$source/$_", "staging/$_"); my $command = "scp"; system $command, @args;` [download] This still requires the chomp, but might make the code more legible or easier to debug and I believe (but not sure) that in some cases it helps with escaping issues.	[reply] [d/l]
Re^2: system call and newline interpretattion. by ikegami (Patriarch) on May 24, 2005 at 15:04 UTC
As a "bonus", using the `system $command, @args` form of `system` is safer since the arguments are not subject to interpretation by the shell.	[reply] [d/l] [select]
Re: system call and newline interpretattion. by davidrw (Prior) on May 24, 2005 at 14:52 UTC
One other comment: Net::SCP might be an alternative for you.	[reply]
Re: system call and newline interpretattion. by robartes (Priest) on May 24, 2005 at 14:35 UTC
Quite possibly your `$_` comes from reading in a line in a file and contains a newline. Try `chomp` before you use `$_`. Then again, as you do not provide context, the problem might be a completely different one. CU Robartes-	[reply] [d/l] [select]
Re: system call and newline interpretattion. by dave_the_m (Monsignor) on May 24, 2005 at 14:37 UTC
Looks like the filename in $_ has a newline in it. Try `chomp` [download] to remove it first. Dave.	[reply] [d/l]
Re: system call and newline interpretattion. by ikegami (Patriarch) on May 24, 2005 at 14:37 UTC
Looks like like $_ ends with a newline. Try adding `chomp` before `$command = ...`. Unrelated, try using `<code>` tags around your code and output when you post.	[reply] [d/l] [select]
Re: system call and newline interpretattion. by tlm (Prior) on May 24, 2005 at 14:37 UTC
How are you getting `$_` ? Are you sure it doesn't end with a newline? the lowliest monk	[reply]
Re: system call and newline interpretattion. by Fang (Pilgrim) on May 24, 2005 at 14:42 UTC
Two thoughts: check all the variables you're using (`$user`, `$ip`, `$_`, etc.) are correctly chomped, especially if some of them are coming from user input, which you didn't mention. From the ouput you provided, it looks to me like `$_` has a trailing newline. use the list syntax of the `system` command, i.e. `system($command, $arg1, $arg2)`, it's always been considered better (as in safer) from what I've read. Update: ah, well, 5 replies and problem solved by the time I submitted this... nevermind me.	[reply]
Re: system call and newline interpretattion. by jaimeGonz (Initiate) on May 24, 2005 at 14:42 UTC
Arrggghhh! That's the sound of me flattening my forehead with the palm of my hand. That's done it. I'd taken a listing from a ls command. chmoped away ... thank you all very much!!!!!	[reply]


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