ZIYAD A. M. AL-BATLY
zamb at saudi.net.sa
Thu May 12 10:43:40 UTC 2005
On Wed, 2005-05-11 at 22:49 -0400, Stephen R Laniel wrote:
> On Wed, May 11, 2005 at 10:38:28PM -0400, mohaham wrote:
> > sh secede2.pl names.txt
> Correct me if I'm wrong, but if that works and just typing
> 'secede2.pl' doesn't, then there's something rather
> odd/serious wrong with his setup. The shell should already
> 1) open the file,
> 2) spot the '#!"
> 3) run the script with the program specified after the '#!'
> If it doesn't do so, that's odd.
No it's not. Unlike DOS/Windows, in Unix and compatible (like Linux,
FreeBSD) the way to find a command to execute goes like this:
1. Is it a command that leads to an absolute *executable* file? If
yes, run that file. Examples: /usr/bin/time, /usr/bin/test,
assuming you are in "/usr": bin/gedit, still assuming you're in
2. Is the command you typed is an "alias"? If yes, expand this
alias and start again with the expanded data. (To see your
current alias(s), type "alias". See the bash manual (man bash)
and read more about alias.)
3. Is it a shell built-in? If yes, run that (no new process will
be created as the shell is already running). Examples are: ls,
cd, time, test. See "man bash" for more built-in(s).
4. Search the directories listed in the environment variable PATH
(try: echo $PATH) from left to right, and try to find an
*executable* with the name you typed. If found, run it.
And that's it! So, when you type "secede2.pl", nothing happens, which
to be expected. Why?
1. To start with, it's not an executable (you need to do "chmod +x
secede2.pl" to make it executable).
2. You didn't supply a command that can lead to a file (no, being
in the same directory as the executable doesn't count (but see
point 3 below)). This is why Some replies told him/her to type
"./secede2.pl", which lead to the file directly (it's in this
directory "./", and it's name is secede2.pl").
3. The current directory is not on your PATH variable. And by the
way, add your current directory to the PATH variable is a very
big security risk! Only add *absolute* directory names only!
4. There is no shell built-in with the name "secede2.pl".
5. When the others said do "sh secede2.p name.txt", what really
happend is that you run/execute the "sh" and pass to it
"secede2.pl name.txt" as variables. "sh", in turn, will check
the first line of "secede2.pl" and see the "#!/usr/bin/perl" and
will execute that application and pass to it "name.txt" as
variable. This why you don't need "secede2.pl" to be executable
in this case, and you don't need to till "sh" it's as "sh", by
default, will search *only* in the current directory.
I hope this helps.
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