$current_path=`echo $cwd` does not work

[Kuhl]

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 .
#

 

[Jürgen Exner]

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

 

[Ron Bergin]

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`;

 

[John Bokma]

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.