Execute bash command and capture output

Question

I have a bash command I'm executing in perl as follows

 @args = ( "bash" , "-c",  "diff <(ssh  -o \"StrictHostKeyChecking no\" user-db01 'mysql -uuser -ppass --execute=\"show databases\"') <(ssh  -o \"StrictHostKeyChecking no\" user-db02 'mysql -uuser -ppass --execute=\"show databases\"')");
system(@args);

but this doesn't allow me to get the output to a string variable. If I execute the exact samething with backticks

 $cmd = "bash -c diff <(ssh  -o \"StrictHostKeyChecking no\" user-db01 'mysql -uuser -ppass --execute=\"show databases\"') <(ssh  -o \"StrictHostKeyChecking no\" user-db02 'mysql -uuser -ppass --execute=\"show databases\"')";
 my $res = `$cmd`;

its throwing an error sh: -c: line 0: syntax error near unexpected token('` What can I do to execute the command and get the result in a variable?

What is the sample code and the exact error from backticks?

DVK
– DVK

2012-08-14 13:19:28 +00:00
Commented Aug 14, 2012 at 13:19 — DVK
– DVK, Commented Aug 14, 2012 at 13:19

DVK · Accepted Answer · 2012-08-14 13:27:00Z

2

You can use one of the usual CPAN modules, e.g. IPC::System::Simple that has a capture() method; or a more-likely-to-be-present IPC::Open2.

Your backticsk problem is that you didn't quote the diff command, thus making it an argument to bash:

BREAKS: bash -c diff <( cmd2 ) <( cmd1 )
GOOD  : bash -c "diff <( cmd2 ) <( cmd1 )"

Your code treats every "word" as a separate argument to your system shell (NOT to bash), e.g. it's the same as calling system("bash", "-c", "diff", " <(ssh" ...)

edited Aug 14, 2012 at 13:27

answered Aug 14, 2012 at 13:21

DVK

130k33 gold badges219 silver badges337 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Aks Over a year ago

When I do a $cmd = "cmd" and then backtick $cmd, the double quotes within cmd are causing problems even if they are escaped

DVK Over a year ago

@Aks - you need to escape the escapes, most likely. A highly annoying excercise, so you should look into CPAN options in my answer.

Collectives™ on Stack Overflow

Execute bash command and capture output

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related