UNIX for Dummies Questions & Answers

What is "not found" in this example?

I create a simple shell script and try to run it....and I get an error....see below.

Thanks!

Fritz

Code:

$ cat > x.sh
echo hello
$ chmod 755 x.sh
$ x.sh
/usr/bin/ksh: x.sh:  not found
$ echo $SHELL
/usr/bin/ksh
$ /usr/bin/ksh
$ /usr/bin/ksh x.sh
hello
$

If the script directory is not in your $PATH variable, then you need to specify a path for the script. So if the script is in your current directory then use...

Code:

./x.sh

...or...

Code:

export PATH=$PATH:$PWD
x.sh

That is amazing to me, that the OS won't look in the current directory if it isn't in the path.

(Lifelong Windows guy here, trying desperately to get a feel for the way this Unix world works.)

But thank you...that solved it!

Fritz

Some people have a dot "." in their PATH variable like:

Code:

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:.

This would look in your current working directory - but for security reasons many leave it away, because if the dot is not placed at the end of the paths and for example someone puts a tool named "ls" in one of your usual working directories, but instead of the good old listing tool of the OS, it might be a program that does something bad to your system, it would be executed 1st instead of the real "ls", living at /usr/bin, because the 1st "ls" found in your paths will be executed. Ok?

It's a conscious design, and a security feature. Many entry-level books explain this. As Zaxxon explains above, it would be frightfully easy to plant a trojan with the same name as a system command (say, ls) in some shared directory, and then lure a user there, or just wait for it to happen.

On single-user systems (and/or systems where security is not seen as very important) you can obviously reason differently about this.