"Strong Scripting Skills" - a definition? - sunday

Sun Jan 25 17:07:41 PST 2004

<quote who="Alvin Oga">
> sometimes grep -v grep is needed, sometimes not... i donno why some
> greps does it differently

Actualy, this is caused by a race condition.

ps -axuw | grep foo | grep -v grep | awk '{print $2}' | xargs kill

Each seperate command gets fork()ed and exec()ed with the pipes setup between
them.

Now, the question is, will the "ps -axuw" initialize and read the process table
before or after "grep foo" is exec()ed.  If before, then "ps -axuw" will not
have "grep foo" in its listing.  If after, then "ps -axuw" will have "grep foo"
in its listing.

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       -MCP