Building Executable Scripts For The Mac OSX Command Line

Yeah bash scripts are nice. Still learning myself. Great for things like automating export/imports for MongoDB and the like.

The bang line is optional if you use the appropriate command from the command line when executing it,

sh

for Bash. So, in either case, instead of using

./build

you can use

sh build

to execute the Bash script.

File permissions: owner, group, everyone. Read access = 4, Write = 2, Execute = 1 (They add up to 7). So to give owner, group, and everyone else all permissions, that's 777. Usually regular files are 644, I think (O=WR, G=R, E=R). Leaving everything else the same, if you just want to make something executable (for everyone), just run `chmod +x [file]`.

To run you need to prefix the script with "./" otherwise the shell will search in your path for a file with this name. With the ./ you tell it to look in the current directory.

Permissions are easy: you have 3 numbers and each corresponds to a permission.

The first number is the owner permission, what you are allowed to do. The second number is the group permission, as each file is marked not just with who owns it, but which group owns it. The third is what everyone else is allowed to do.

Each number is a very simple 3-bit mask. From left (most significant) to right (least significant) you have r, w, x, or Read, Write, Execute.

So what does 777 mean? Each 7 in binary is 111, which means a combination of Read, Write, and Execute, for all 3 permissions. In other words, anyone can do anything they want with the file, including change it!

Also, this is why permissions print out the way they do when you do a directory listing: rwxrwxrwx. That's a bitmask, where each letter is a one and each dash is a zero.

Generally, for shell scripts you probably want to go with 744: you have full control, but others only have read access. If you're paranoid you could go with 700, so that you have full control but no one else can do absolutely anything with it.

The "chmod" utility makes this easy, too. If you want to set a file so that it's only executable for you, instead of remembering numbers and bitmasks you can say "chmod u+x whatever". That means "give the User Execute access".

"So, it's basically like Bash creating another bash process to execute the script? [...]"

I'm not sure if that's how Node.js will work that's how it works for bash. It will fork itself into executing the script.

@Ben,

You're right. bash is indeed the default shell for the most recent 2 or 3 versions of Mac OS X. Snow Leopard and Lion for sure. Not too sure about Leopard. Pretty sure Tiger and all preceding big cats defaulted to tcsh ("tee cee shell"). tcsh is very similar bash but Apple wanted to attract Linux users to Mac OS X, and bash is the default on Linux.

You should still specify shell at the start of scripts that you want to share with others, in case they use a different shell. I'm a C coder, so I still prefer the syntax of tcsh. The only time I ever use bash is when I need to redirect stderr, usually to throw it away (bash -c "my_script options 2>/dev/null", for example).

Happy scripting.

P.S.: That's how you specify shell outside the script. If I had specified it in the script, the bash -c would've been unnecessary.

... assuming the 2>/dev/null occurred in the script too that is. (Sheesh, mixing shells can get confusing.)

You should check out iTerm2 for your terminal needs - its better than the default Terminal the Mac comes with.

I've had to use a lot of unix utils for my job and they are definitely very powerful and fast. It is crazy how much raw data processing can be handled with the built-in unix tools.

This link has a bunch of useful utils that will come in handy at some point or the other:
http://www.quora.com/Linux/What-are-some-time-saving-tips-that-every-Linux-user-should-know

@Eapen,

You're right. About the only amazingly cool thing that Terminal has going for it is drag-and-drop of files and folders into the terminal window for command line completion.

Another cool terminal app for Mac is X11 from Apple (/Applications/Utilities/X11.app), which conveniently implicitly supports the X windowing system. It allows me to use the "Nirvana Editor" (command name "nedit", from nedit.org), which provides a very Mac-like set of keyboard combinations and syntax coloring. So nice to use Ctrl-C to mean Copy instead of Kill Foreground Process.

Hi Ben,

The `#!/bin/bash` is commonly referred to as the sha-bang (or she-bang or sh-bang), which is derived from sharp (#) and bang (!). I believe you'll need to make that the very first line of your script file, otherwise the command interpreter will just interpret (ignore) it as a comment. Then again, bash is probably your default command interpreter anyway, and it also doesn't look like you've used any bash-specific commands.

You do need to be careful about path/current directory in your scripts. Your example script works only if you call it as ./build, with your terminal working directory at the location of your script. Let's say you've located the script at /opt/bash/build, and you call it from a different location--say, /Users/Ben/--with the command `/opt/bash/build`. This will execute the script fine, but the initial command of `cd ./js/` will change the working directory to /Users/Ben/js/, not /opt/bash/js/. So, you might instead set a variable to your base directory, by leveraging the dirname command and the $0 variable, which holds the path to the script being executed:

project_directory=`dirname $0`

So, your cd command would then become:

cd "${project_directory}/js/"

Or, you might just use this one-liner, instead of changing the working directory:

node "$(cd `dirname $0` && cd ..)/r.js" -o "$(cd `dirname $0`)/js/app.build.js"

I'm far from a shell scripting guru, but I've really enjoyed the bash scripting I've gotten into, and have been able to make frequent use of bash scripts (and the very many very crazy powerful UNIX programs, like sed!). Here are some good links for you, whenever you feel like getting your bash geek on some more ;-)

http://tldp.org/LDP/Bash-Beginners-Guide/html/Bash-Beginners-Guide.html

http://tldp.org/LDP/abs/html/

http://www.gnu.org/software/bash/manual/bashref.html

Cheers!
Jamie

@Ben,

LOL @ "I just want to pipe something into something else! :D"

I know, piping is still just so cool, and useful everywhere. Have a look at the sed command--it's a crazy powerful stream editor, and you can pipe stuff to sed all day long ;-)

http://www.grymoire.com/Unix/Sed.html

As for the ${}, the curly braces aren't always needed to output a variable in Bash, but they're helpful within certain strings.

Consider this...

#!/bin/bash
 
my_string=something
 
# This outputs "something and something else"
echo "$my_string and something else"
 
# This also outputs "something and something else"
echo "${my_string} and something else"
 
# This outputs "something_and_something_else"
echo "${my_string}_and_something_else"
 
# But this would just echo an empty string
# (variable my_string_and_something_else is empty/not defined)
echo "$my_string_and_something_else"

So, simple variable output in a string is fine, as long as the variable name is not followed by a character that would be a valid part of the variable name. The curly braces are slightly more verbose, but can be a safe habit.

Great post, Ben. Coincidentally, I'm currently working on a set of "Beginning CentOS" posts for my blog that are along the same lines -- semi-introductory tasks on a Linux platform, for someone new to the OS...like me. :)

Repeat after me, UNIX is wonderful :-)

@Tom, UNIX is wonderful :D

Better be careful Ben. Pretty soon you will changing your config files with sed, parsing log files with awk, grepping all over the place and running cron jobs instead of use CF scheduled tasks. But you should really worry when you start writing your code in vi.
I use bash scripts to start and stop CF, clean out parsed files etc. If I am forced to use a Windows machine the first thing I do is install Cygwin so I have access to *nix like command line.