UNIX for Dummies Questions & Answers

So, here's the deal... I was attempting to type this:

Code:

>  grep -R "searchterm" *

and somehow I typed this instead:

Code:

>  grep -R "searchterm"

>   *

I accidentally typed "space-asterisk" on the second prompt. This apparently caused Bash to attempt to run the first file in the pwd, which happened to have *something* that spawned a load of processes and killed my server (a VPS with fixed process count). I've never seen this. Can anyone explain the "space-asterisk" phenomenon? It seems like the sort of thing that's a subset of a bigger form of command line trickery and awesomeness, but I can't seem to put together the right search terms to get Dr. Google to explain it to me...

When you execute the command

Code:

>  grep -R "searchterm" *

the asterisk is first expanded to all files and (and other items) in the current directory. So for example if the directory contains the files

Code:

first 
second
third
(and so on)

then the command becomes:

Code:

>  grep -R "searchterm" first second third (and so on)

What happened in your case was that the first command failed and then the second command was executed, which expanded to:

Code:

 first second third (and so on)

where 'first' is the command and 'second' 'third' are the parameters.

Normally there is a safeguard and 'first' would not be executed since a command is only recognised as a command by the OS if it either is called as <path>/command (e.g. ./first) or it is located in a directory that is part of you search path (the variable "PATH").

My guess would be that there was either:
- a '.' in your search path ( which would illustrate one of the biggest dangers of this practice ), or
- the current directory happened to be in the PATH variable, or
- the name of command happened to be the same as a command in one of the directories in the PATH variable.

For the command to wreak this much havoc you were probably executing the command as root?

S.