Obey Files

Can Obey files take parameters on the command line, in the way that DOS Batch files and UNIX shell scripts can? (If so, how?)

Can I change the type of a file programmatically (i.e. in an obey file)?

And a long shot: in a UNIX shell script I can read the output of a command by surrounding it with backticks (`). Is this possible in RISC OS? Unlikely, I know, but…

Can Obey files take parameters on the command line, in the way that DOS Batch files and UNIX shell scripts can? (If so, how?)

Yes. %0 is the first parameter, %1 the second, etc. You’d use %*0 to give you all the parameters as a single string, or %*1 for all but the first, etc. For this reason, you need to use %% to escape a single % sign in an obey file.

Unlike shell scripts, there’s no system variable (AFAIAA) that holds the name of the obey file itself. There is, however, Obey$Dir to tell you where the obey file was executed from. Why there isn’t a corresponding Obey$File, I’ve no idea.

Can I change the type of a file programmatically (i.e. in an obey file)?

SetType <type name|number>

And a long shot: in a UNIX shell script I can read the output of a command by surrounding it with backticks (`). Is this possible in RISC OS? Unlikely, I know, but…

Only in a fairly cludgy way, via redirection of output to a file using curly braces and the greater than sign (use > to write or >> to append).

See this post for an example that does most of this.

Can Obey files take parameters on the command line, in the way that DOS Batch files and UNIX shell scripts can? (If so, how?)

Yes. The parameters will come through as %0, %1, %2, etc. You can also do things like use %*1 to get all the parameters from %1 and up (useful if you need to pass a bunch of parameters on to another command/tool)

Can I change the type of a file programmatically (i.e. in an obey file)?

*SetType

And a long shot: in a UNIX shell script I can read the output of a command by surrounding it with backticks (`). Is this possible in RISC OS? Unlikely, I know, but…

Not supported, I’m afraid. But depending on your needs, you can make use of redirection. But be aware that RISC OS does redirection differently than other OS’s; with C programs you can use the standard > and < redirection operators directly, but with arbitrary commands you need to place the redirection operators in {}. E.g. “*echo foo { > temp }”

There are basically two tricks I know of for using redirection to process the output of a command:

1. Have a dummy obey file containing a single line: "set myvar ". Make sure there’s a space on the end of the line (some editors may strip it automatically), and make sure there’s no newline character. Then make your script copy the dummy obey file to a temporary location, run the command you want using redirection to append to the obey file, and then execute the obey file in order to set the system variable to the output of the command. This obviously only works if the command produces a single line of output!
2. Redirect the output to a temporary file and then use grep to look for specific text. Check <Sys$ReturnCode> to see if grep returned 0 or 1 for match/no match.

Bah, beaten to the post!

:P

Edit: If you’re using the RISC OS Pi distro, you should have a copy of the PRMs on the disc, in Documents.Books.PRMs. The specific chapter you’ll want to see is in PRM4, starting on page 351 (“Command scripts”).

See this post for an example that does most of this.

The syntax is ok, but I am not sure that it is at all reliable. I may have some special circumstances on the RISC PC I did the testing on. Do not rely on it, but use the method Jeffrey suggested.

One thing that is miles better in this area on RISC OS when compared to Linux is aliases have parameters, in much the same way as obey files. So your alias can do things like reorder the parameters before passing them on to whatever is aliased. I’m pretty sure you can’t do that in bash, for example. /me waits for someone to prove him wrong.

Don’t forget PipeFS too.
http://www.riscos.com/support/developers/prm/pipefs.html

Unlike shell scripts, there’s no system variable (AFAIAA) that holds the name of the obey file itself. There is, however, Obey$Dir to tell you where the obey file was executed from. Why there isn’t a corresponding Obey$File, I’ve no idea.)

Perhaps because there’s no obvious need—after all, the file knows what its name is. On UNIX-like systems, with hard links, a file may have several different names. The text editor e3 uses this feature to specify the key mapping—e3ne for NEdit,e3me for MicroEmacs, the default is WordStar (I think). It’s a very nice console-mode text editor, very small, needs no shared libraries, but will never run on RISC OS—it’s written in X86 assembler.

the file knows what its name is

Kind of. Unless you want your obey file to be a template for multiple files, or you have a process which renames/copies it. Then you have to do a search and replace operation within the obey file. Plus, if and when we get symbolic links, we’d just have to add this anyway… :)