Shell Programming and Scripting

In POSIX shell, we don't have arrays, but we can iterate over a list like this:

Code:

#!/bin/sh
list="Fred Barney Wilma Betty"
for i in $list; do echo $i; done

Fred
Barney
Wilma
Betty

But let's say we want "Mr. Slate" in the list.
We know we can't just stick him in there like this:
list="Fred Barney Mr. Slate"
Because word splitting would split Mr. Slate into two words.

So, we could play with IFS

Code:

#!/bin/sh
list="Fred:Barney:Mr. Slate"
IFS=:
for i in $list; do echo $i; done

Fred
Barney
Mr. Slate

But what if we don't want to fool with the IFS.
We could use eval

Code:

#!/bin/sh
list='Fred Barney "Mr. Slate"'
eval '
    for i in '$list'; do 
        echo $i
    done
'
Fred
Barney
Mr. Slate

Notice we had to put literal quotation marks around Mr. Slate in the list. That's understandable.
Had to use single quotes to mark the beginning and end of eval block.
And had to make sure $list is NOT in single quotes.

This works, but it's kind of clumsy.
Is there a better way? Without messing with IFS and keeping with POSIX sh.

The reason I say this: when I do an eval block, it doesn't get the nice syntax highlighting in my editor! (gvim) It seems whenever I do an eval block, I never get it right the first time. Or second time!

Sometimes I do the eval thing within a function, as a way of "passing by reference" (I think that's what it's called). I know Bash has references. I'm trying to get in the habit of "portable" scripting. Or at least, make it run in Dash.

-MD

If the list is in a file, then you can do this:

Code:

while read $name ; do
     echo $name
done < $file

You can also do the below style; makes it eaiser to add/remove (you can also do a comment-out mechanism using # by doing grep -v "^#" in the while).

Code:

list=$(cat <<-LIST
Fred
Barney
Mr. Slate
# Mr. Skipped
LIST
)
echo "${list}" |grep -v "^#"|while read $name ; do
     echo $name
done

I don't think there is anything radical we can do with purely shell.

You can emulate arrays using positional parametrs:

Code:

$ set -- Fred Barney "Mr. Slate"
$ for e;do printf '=>%s<=\n' "$e";done
=>Fred<=
=>Barney<=
=>Mr. Slate<=

Code:

$ set -- Fred Barney "Mr. Slate"

How do we set, if the list in a variable?

Try...

Code:

$ list='Fred Barney "Mr. Slate"'
$ eval set -- "$list"
$ for i
> do echo $i
> done
Fred
Barney
Mr. Slate
$

Thanks - had been trying this for a while.