storing the output of a external command to a variable using bactticks in perl

Question

I am usiing the following code to store the output of an external command in a variable. But when I print the error, I get nothing.

$error1 = `hadoop fs -copyFromLocal $src_dir $tgt_dir`;
print "$error1\n";  # --> prints nothing

The output of the command in ` ` is:

copyFromLocal: Cannot create file/user/file5._COPYING_. Name node is in safe mode.

Is there anything wrong in storing the output?

stackoverflow.com/a/778797/635608

Mat
– Mat

2015-01-25 09:47:05 +00:00
Commented Jan 25, 2015 at 9:47 — Mat
– Mat, Commented Jan 25, 2015 at 9:47

brian d foy · Accepted Answer · 2015-01-25 13:11:23Z

1

The backticks in Perl only capture standard output. If hadoop is sending the message to standard error instead, backticks won't capture it. See the perlfaq answer for How can I capture STDERR from an external command? for several ways to do it. The simplest is to redirect the standard error file descriptor into the standard output file descriptor with 2>&1:

$error1 = `hadoop fs -copyFromLocal $src_dir $tgt_dir 2>&1`;

Modules such as Capture::Tiny are very nice as well.

answered Jan 25, 2015 at 13:11

brian d foy

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