"do shell script" returns different from Terminal. Why?

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Level 1

5 points

"do shell script" returns different from Terminal. Why?

Hi all,

I'm a novice by all means, so I might be missing the obvious. However, I wanted to have a little AppleScript that returns the SHA1 hash of a string. My results were different from other ways of getting the same hash, so in the end I went and copied into Terminal what AppleScript shows it did. The hashes are different, which I don't understand. I tried to research some character encoding issues, but did not find anything (everything should be Unicode, and that's it).

Could you help me sort out what's going on, and how I could get the hash I want (the same as in Terminal)? Thanks!

Excerpt from AppleScript Editor Result pane after run:
do shell script "echo -n 'RolfAaberge'|openssl sha1"
--> "683acf2937e0a3cd7817a6cd466104b46204c575"

Excerpt from Terminal after run:
echo -n 'RolfAaberge'|openssl sha1
b2f0b01f414f709f311f233633b91bdd5c08ae6a

MacBook (2006 August), Mac OS X (10.6.2)

Posted on Nov 21, 2009 9:05 PM

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Answer 1

red_menace

Level 6

17,066 points

Nov 21, 2009 10:07 PM in response to iLac

It looks like the shell built-in command uses a different encoding, so using printf or the standalone echo should give more consistent results:

do shell script "/bin/echo -n 'RolfAaberge'|openssl sha1"

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Answer 2

iLac Author

Level 1

5 points

Nov 21, 2009 10:15 PM in response to red_menace

Thanks! But why should "/bin/echo" be different from simply "echo"? Or if not, how could I use printf, as you suggested?

Thank you, really.

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Answer 3

red_menace

Level 6

17,066 points

Nov 21, 2009 10:23 PM in response to iLac

When you just type 'echo' you will get the built-in command from the shell (typically bash), while '/bin/echo' is a separate stand-alone command. The 'printf" command has a lot of formatting, but in this example it can be used just like the echo:

do shell script "printf 'RolfAaberge'|openssl sha1"

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Answer 4

iLac Author

Level 1

5 points

Nov 21, 2009 10:40 PM in response to red_menace

This solved it indeed! /bin/echo was enough to do the trick.

Thanks a lot!

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Answer 5

Nov 24, 2009 5:06 PM in response to red_menace

But why should the two versions of 'echo' produce different results? Both are just writing simple sequences of Ascii characters to stdout? If I compare the direct output of the two echos, they match exactly, so why should "openssl sha1" perform differently?

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Answer 6

etresoft

Level 9

56,740 points

Nov 24, 2009 5:29 PM in response to Ken Nellis

There is only one version of echo. It is being called two different ways. When the full path is used, it calls the program directly and passes all the arguments to it. When the full path is omitted, it has to use the shell to find echo, passing all the arguments to the shell, which then sends them on to echo.

When run with the full path (or from the terminal), "-n 'RolfAaberge'" results in "RolfAaberge". When called via AppleScript without the full path, the results are "-n 'RolfAaberg'"

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Answer 7

Nov 24, 2009 6:18 PM in response to etresoft

Your explanation does not mesh with my observations. Using OS X 10.4 and ScriptEditor 2.1.2,

do shell script "builtin echo -n 'RolfAaberge'"

results in

"RolfAaberge"

without any -n in the output. Could the different versions of our software explain the difference?

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Answer 8

Nov 24, 2009 6:20 PM in response to Ken Nellis

I get the same result with

do shell script "echo -n 'RolfAaberge'"

, which is what I meant to post.

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Answer 9

etresoft

Level 9

56,740 points

Nov 24, 2009 6:36 PM in response to Ken Nellis

qen wrote:
Could the different versions of our software explain the difference?

It looks like it. When I do


do shell script "builtin echo -n 'RolfAaberge'"

in script editor, I get: "-n RolfAaberge"

If I just run "sh" and enter "echo -n 'RolfAaberge'", I still get "-n RolfAaberge". When running bash, I get "RolfAaberge". I know that "do shell script" uses sh.

These shell builtins are only for interactive use. You should always use the executable form from any kind of script.

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Answer 10

Nov 24, 2009 6:54 PM in response to etresoft

{quote}etresoft wrote:
These shell builtins are only for interactive use. You should always use the executable form from any kind of script.{quote}
Never say never; also never say always.
If you want portable shell scripts you won't use paths because the binary isn't always found in the same place, e.g., /bin, /usr/bin, /sbin, /usr/sbin, etc.

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Answer 11

etresoft

Level 9

56,740 points

Nov 24, 2009 7:21 PM in response to Ken Nellis

qen wrote:
If you want portable shell scripts you won't use paths because the binary isn't always found in the same place, e.g., /bin, /usr/bin, /sbin, /usr/sbin, etc.

I don't want portable shell scripts. I want reliable shell scripts. I don't want some user's custom-built software running with my shell scripts.

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