Beefy Boxes and Bandwidth Generously Provided by pair Networks
Keep It Simple, Stupid
 
PerlMonks  

comment on

( [id://3333] : superdoc . print w/replies, xml ) Need Help??
The multi-arg usage of system() is good -- somebody needed to point that out (and I'll explain it for the OP).

But the "or die" part is wrong: system() will return the exit status of the process, which is based on shell semantics: a return value of zero means "success" (i.e. "good") whereas any non-zero value means "failure" (i.e. "bad") -- so you probably want to say "and die" instead. But that's confusing, so it's usually better to say it like this:

my $err_stat = system( $prog, @args ); die "system failed on $prog @args: $?" if $err_stat;
(update: my apologies -- I missed the "== 0" part in borisz's post.)

As to the reason for the multi-arg usage, the difference between this:

system( "$prog @args" );
and this:
system( $prog, @args );
can be demonstrated harmlessly if $prog is set to something like "cat" and any element of @args is set to something like "\$HOME/.bashrc; echo I could delete everything right now".

In the multi-arg usage (the latter choice), each element of @args is passed directly to the "argv" array of "cat" -- if an arg does not map to a readable file name, cat reports an error. In the single-string command-line case, the whole string is passed to a shell, and the shell executes the string. If the string happens to contain workable instructions that you don't expect or don't want, you could be in for a nasty surprise.


In reply to Re: Re: system call not working by graff
in thread system call not working by Melanie

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.