Can I echo local variable via ssh into remote file?

Question

I try to write variable in end of file, but write it into STDOUT in local server some code:

$num = <STDIN>
my $cmd = "echo $dep_keys{$num} >> /root/1";
#$ssh->system({stdin_data =>$dep_keys{$num} },"echo >> /root/1");
#$ssh->error die "Couldn't establish SSH connection: ". $ssh->error;
#$ssh->system("echo $dep_keys{$num} >> /root/1");
$ssh->system($cmd);

I expect that the file will contain new line in the end of file.

The first problem here is that you're not using strict and warnings. The second problem is that $num will usually contain a trailing newline after reading from STDIN, so you should use chomp on it. — Grinnz
– Grinnz, Commented Sep 27, 2019 at 16:48
The variable is interpolated locally into that string, so it is not a variable anymore on the remote system, and by enabling warnings you will be informed that it is probably just undefined because you didn't chomp $num. — Grinnz
– Grinnz, Commented Sep 27, 2019 at 16:50
The third problem is that you aren't sanitizing the variable for use in a shell command, which you can use String::ShellQuote to do. — Grinnz
– Grinnz, Commented Sep 27, 2019 at 16:51

ikegami · Accepted Answer · 2019-09-29 06:39:49Z

1

use String::ShellQuote qw( shell_quote );

defined( my $num = <STDIN> )
   or die("Invalid input");

chomp($num);

defined($dep_keys{$num})
   or die("Invalid input");

my $cmd = shell_quote('printf', '%s\n', $dep_keys{$num}) . ' >>/root/1';
$ssh->system($cmd);

Fixes:

Checks for EOF and other invalid inputs.
Removes trailing line feed from $num (if any).
Properly convert the text from the hash element into a shell literal.
Avoids echo because echo makes impossible to output some strings.

answered Sep 29, 2019 at 6:39

ikegami

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