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Hi, all:

Backticks `` are supposed to be able to transfer the result of shell
commands to Perl variable.
But it's very confusing that it does not behave in the way that I
think it should do.

$current_path=`pwd`; This works.
$current_path=`echo $cwd`; This does not work.

But in fact, pwd is aliased to echo $cwd. Details see below.

What's the issue? How to fix it?

Thanks.


# which pwd
pwd: aliased to echo $cwd
# pwd
/home/user/shell
# echo $cwd
/home/user/shell

#!/usr/bin/perl
$current_path=`pwd`;
print "\nCurrent path is $current_path .\n";
$current_path=`echo $cwd`;
print "\nCurrent path is $current_path .\n";
$current_path=`echo \$cwd`;
print "\nCurrent path is $current_path .\n";
$current_path=`"echo $cwd"`;
print "\nCurrent path is $current_path .\n";
exit 0;


But the result of this script is:

Current path is /home/user/shell
..

Current path is
..

Current path is
..
sh: line 1: echo : command not found

Current path is .
#

Kuhl <> wrote:
>Hi, all:
>
>Backticks `` are supposed to be able to transfer the result of shell
>commands to Perl variable.
>But it's very confusing that it does not behave in the way that I
>think it should do.
>
>$current_path=`pwd`; This works.
>$current_path=`echo $cwd`; This does not work.
>
>But in fact, pwd is aliased to echo $cwd. Details see below.

A guess: those aliases are not valid in your _system_ shell but only in
the shell that you are using as your standard shell from the command
line?

Try calling print `alias` to find out, if those aliases are even
defined.

jue

On Sep 27, 7:10 am, Kuhl <chen_zhi...@yahoo.com> wrote:
> Hi, all:
>
> Backticks `` are supposed to be able to transfer the result of shell
> commands to Perl variable.
> But it's very confusing that it does not behave in the way that I
> think it should do.
>
> $current_path=`pwd`; This works.
> $current_path=`echo $cwd`; This does not work.
>
$cwd is being seen as a Perl scalar that is interpolated by Perl
before passing it to the shell...you need to escape it.

$current_path=`echo \$cwd`;

Kuhl <> wrote:

> Hi, all:
>
> Backticks `` are supposed to be able to transfer the result of shell
> commands to Perl variable.
> But it's very confusing that it does not behave in the way that I
> think it should do.
>
> $current_path=`pwd`; This works.
> $current_path=`echo $cwd`; This does not work.

[..]
> #!/usr/bin/perl

use strict;
use warnings;

and all becomes clear. It does work, you only misunderstand ``.

There is a very good reason why those two lines are recommended daily in
this group.

--
John http://johnbokma.com/ - Hacking & Hiking in Mexico

Perl help in exchange for a gift:
http://johnbokma.com/perl/help-in-ex...or-a-gift.html