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Top Forums Shell Programming and Scripting don't know how to interpret this Post 302503452 by Corona688 on Thursday 10th of March 2011 03:20:12 PM
Old 03-10-2011
Quote:
Originally Posted by Straitsfan
I guess I just should have asked what the statement

$listpage

means -- does it mean to display the value of listpage, and if so, why didn't it use the echo command?
Think more literally. It's just a variable, and the shell does the same thing with variables for every statement whether they're at the beginning of the line or the end. For each statement, the shell
1) Splits apart on semicolons or pipes, and evaluates each part(turns variables into their contents, etc).
2) Executes each part.
Code:
CMD="echo"
$CMD asdf

will print 'asdf' because it
1) converts $CMD asdf into echo asdf
2) runs "echo asdf".

Now this:
Code:
CMD="ls | more"
$CMD

does this:
1) Converts $CMD into ls | more
2) Executes ls | more

See something wrong? Pipes were supposed to be handled in step 1 but weren't, because it was in a variable. Step 2 doesn't do anything to pipes, so just feeds it into ls raw. ls complains there's no such files "|" and "more".

Now this:

Code:
CMD="ls | more"
eval "$CMD"

1) Converts eval "$CMD" into eval "ls | more"
2) Executes eval "ls | more", shoving the string "ls | more" back into step 1.
1) Splits ls | more into two statements, ls and more
2) Executes ls, piping it into more.

eval's just a special keyword that bumps the shell back into step 1.

Last edited by Corona688; 03-10-2011 at 04:25 PM..
 

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shell(1F)							   FMLI Commands							 shell(1F)

NAME
shell - run a command using shell SYNOPSIS
shell command [command] ... DESCRIPTION
The shell function concatenate its arguments, separating each by a space, and passes this string to the shell ($SHELL if set, otherwise /usr/bin/sh). EXAMPLES
Example 1: A sample output of shell command. Since the Form and Menu Language does not directly support background processing, the shell function can be used instead. `shell "build prog > /dev/null &"` If you want the user to continue to be able to interact with the application while the background job is running, the output of an exe- cutable run by shell in the background must be redirected: to a file if you want to save the output, or to /dev/null if you don't want to save it (or if there is no output), otherwise your application may appear to be hung until the background job finishes processing. shell can also be used to execute a command that has the same name as an FMLI built-in function. NOTES
The arguments to shell will be concatenate using spaces, which may or may not do what is expected. The variables set in local environments will not be expanded by the shell because "local" means "local to the current process." ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
sh(1), attributes(5) SunOS 5.10 5 Jul 1990 shell(1F)
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