by default should wait until script1.pl finish?.

Yup. In fact, the only exception is in Windows when using the special system(1, ...); syntax.

Of course, if script1.pl launches a child and exits, the main script won't wait for the grandchild to complete. By the way, that means system("command &"); will cause system to return "immediately". (The child, sh, launches command and exits without waiting for command to exit.) Just remove that & if you have it.

Then what do you think is the cause of my symptom above?

Based on the limited information at hand, all I can say with reasonable certainity is that output.txt does not exist.

In reply to Re^3: Synchronizing Multiple System Processes by ikegami
in thread Synchronizing Multiple System Processes by neversaint

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


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.