problem with sed on command line

[Paul]

Hello,

I am struggling to find a solution to the following apparently simple
problem, so any help would be much appreciated.

Here is a simple example of what I'm trying to do.

From the console of a linux machine running Fedora-12, if I do

echo "AB" > file
FILE=file

sed "s/AB/12/" $FILE

I get, as expected,

12

I can also do

COMMAND="sed s/AB/12/ $FILE"
$COMMAND

and again I get

12

So far so good. If, however, I now introduce a space with

echo "A B" > file

I'd like to find the setting for COMMAND which is equivalent to

sed "s/A B/1 2/" $FILE
1 2

I've tried a number of obvious variations, but I can't get any to
work, for example,

COMMAND="sed s/A B/1 2/ $FILE"
$COMMAND
sed: -e expression #1, char 3: unterminated `s' command

COMMAND="sed \"s/A B/1 2/\" $FILE"
$COMMAND
sed: -e expression #1, char 1: unknown command: `"'

COMMAND='sed "s/A B/1 2/" $FILE'
$COMMAND
sed: -e expression #1, char 1: unknown command: `"'

COMMAND="sed 's/A B/1 2/' $FILE"
$COMMAND
sed: -e expression #1, char 1: unknown command: `''


Thanks,

Paul

[Chris Miller]

cmiller@elder-miller-ubuntu:~/tmp$ echo "A B" > foboar.
cmiller@elder-miller-ubuntu:~/tmp$ sed "s/A\ B/1\ 2/" foboar.
1 2

You need to escape the whitespace with a backslash (or backwhack in
Microsoft-nese, for those interested).

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[Daniel Eggleston]

You don't need to escape the spaces (try it - do exactly what cmiller did, without the backwhacks, and it will work fine).

However, Paul's storing the data in a variable, and the double quotes get passed to the sed command verbatim, and sed can't handle the quotes. 

One easy solution is to use a couple of variables, instead of one:

[ degglest@tavanasa : /net_home/degglest ]
$ COMMAND='sed'; ARG='s/A B/1 2/'
[ degglest@tavanasa : /net_home/degglest ]
$ echo "A B" | $COMMAND "$ARG"
1 2

           Daniel

[Paul Stansell]

Dear Daniel,

Thanks very much for your example, it's exactly what I needed!

Paul