conditioning system shell output from within Perl - Noob

[jason]

When I execute the folloing at the HPUX Posix shell

diffmsg=`scripts/cdiff.sh`
print $diffmsg

I get the echo output from that script.

However, inside Perl, apparently once the shell system call closes,
that environment variable is gone as $diffmsg never has anything in
it.

system "diffmsg=`scripts/cdiff.sh` ";
$diffmsg = ($ENV{'diffmsg'});

Am I correct in my findings?

Any easy way to be able to condition the output from this shell script
in perl? I'm hoping without having to open, read and close a file.

Thanks.

 

[Keith Keller]

When I execute the folloing at the HPUX Posix shell

diffmsg=`scripts/cdiff.sh`
print $diffmsg

I get the echo output from that script.

However, inside Perl, apparently once the shell system call closes, ^^^^^^^^^^^
that environment variable is gone as $diffmsg never has anything in
it.

That's because once the system call is done, the shell where the
variable was set is also gone (if one was called).

Any easy way to be able to condition the output from this shell script
in perl? I'm hoping without having to open, read and close a file.

perldoc -q output.*system

--keith

 

[Tad McClellan]

However, inside Perl, apparently once the shell system call closes,
that environment variable is gone as $diffmsg never has anything in
it.

Yes, that is standard Unix process model stuff, the same with any
programming language.

A child cannot affect it's parent's environment.

system "diffmsg=`scripts/cdiff.sh` ";

Any easy way to be able to condition the output from this shell script
in perl?

Yes.


I'm hoping without having to open, read and close a file.

Well you *are* going to have to open and read the documentation
for the system() function.

I gotta wonder how it is that you haven't done that already...

It says right in there how to capture the output from external programs.

 

[Sherm Pendley]

Any easy way to be able to condition the output from this shell script
in perl? I'm hoping without having to open, read and close a file.

As far as the environment variable being visible to the parent Perl app,
that's a FAQ. Have a look at "perldoc -q environment".

But you don't need an environment variable at all - just capture the
output of scripts/cdiff.sh directly. Backticks work in Perl the same way
they do in your shell, so in Perl do:

my $diffmsg = `scripts/cdiff.sh`;

sherm--

 

[Tintin]

When I execute the folloing at the HPUX Posix shell

diffmsg=`scripts/cdiff.sh`
print $diffmsg

I get the echo output from that script.

However, inside Perl, apparently once the shell system call closes,
that environment variable is gone as $diffmsg never has anything in
it.

system "diffmsg=`scripts/cdiff.sh` ";
$diffmsg = ($ENV{'diffmsg'});

Am I correct in my findings?

Any easy way to be able to condition the output from this shell script
in perl? I'm hoping without having to open, read and close a file.

The following two shell scripts should answer your question.

#!/bin/sh
echo "script1"
../script2
echo "$diffmsg is not set because my child process has completed"

#!/bin/sh
echo "script2"
diffmsg='foo'
export diffmsg