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I'm getting more comfortable with the terminal in Mac OSX and I thought I'd have a dabble at bash scripting. Not wanting to crawl before I could sit down I wanted to write an incredibly simple "Hello, world!" script so I did this:

~/Desktop touch hello.sh
~/Desktop vim hello.sh

I then added this to hello.sh

#!/bin/bash
echo "Hello, world!"

I then did this:

~/Desktop chmod -x hello.sh
~/Desktop hello

At which point nothing happened.

I had downloaded an equally simple bash script from somewhere that was this:

#!/bin/bash
echo "The current date and time."
date

And when I did

~/Desktop date

it did exactly what it was supposed to.

So then I checked file permissions with ls -l and I got this:

-rw-r--r--    1 Mike  staff       33  5 Sep 21:13 hello.sh
-rw-r--r--@   1 Mike  staff       50  5 Sep 21:00 date.sh

So clearly the @ is making all the difference, or so I thought. Instead of using vim I created the same file in TextEdit and after going through the same motions as before I ended up with the same situation, ie my script did nothing except now the permissions were showing an @ at the end of them.

So my questions are why is this not working, what am I doing wrong? And what is the @ at the end of the permissions?

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1 Answer 1

up vote 8 down vote accepted

First, you must add the "execute" permission bit. Using chmod +x adds it, chmod -x removes it.

Second, in Unix you must use the exact file name. If the file is named hello.sh, you must run it by hello.sh, not hello. (You probably are used to Windows and its %PATHEXT%, which does not exist in Unix. Here, only the execute bit is considered and .sh is meaningless to the system – the file can be named simply hello if you want.)

Third, by default the current directory is not searched for commands (for security reasons). Either the script must be located in your $PATH, or you must run it by its full path name. Using . (which means "the current directory") will suffice.

~/Desktop chmod +x hello.sh
~/Desktop ./hello.sh
Hello, world!
~/Desktop ~/Desktop/hello.sh
Hello, world!
~/Desktop

(./hello.sh means "hello.sh in the current directory".)

When you typed date, you did not run your own script; you ran the system's date command (just like you run the system's chmod command when you type chmod). The @ is not making a difference here.

The @ character simply indicates the presence of "extended metadata" associated with that file; most likely something specific to TextEdit. According to the ls(1) manual page, you can use ls -l -@ (ls -l@) to see the metadata.

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Thank you very much, a perfect answer. It's working as I expect now. –  MrMisterMan Sep 5 '11 at 20:47

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