assigning SED output to a variable = trouble!

Shell Programming and Scripting
1

i'm on a Mac running BSD unix.

i have a script in which i ask the user to input the name of a mounted volume. i then call SED to substitute backslashes and spaces in place of the spaces. that looks like this:

echo "Enter the name of the volume"
read Volume
echo "You've chosen \"$Volume\""
# remove spaces from name of Volume
echo $Volume | sed 's/ /\\ /g'

if i enter "old mac hd" for the volume name when prompted, it returns with:
"old/ mac/ hd" which is perfect!

but... if i then want to assign this output to a variable for later use, it doesn't work:

uVolume=`echo "$Volume" | sed 's/ /\\ /g'`
echo $uVolume

this returns:
"old mac hd" and NOT "old/ mac/ hd" as i'd like. and, as i'll be using the full directory path in a later portion of the script, i kinda need those backslashes!

i'm assuming that i'm missing simple syntax here. thoughts/comments/questions?

2 
uVolume=`echo "$Volume" | sed 's/ /\\\ /g'`

If you are using bash, you can do it without any external commands:

uVolume=${Volume// /\\ }
3

Worked for me:

$ cat ll.sh
echo "Enter the name of the volume"
read Volume
echo "You've chosen \"$Volume\""
# remove spaces from name of Volume
echo $Volume | sed 's/ /\\ /g'


$ sh ll.sh
Enter the name of the volume
old mac hd
You've chosen "old mac hd"
old\ mac\ hd

FYI: Im running CentOs 5.2 (Red Hat)

4

That's exactly what hungryd said: It works when sent to the standard output.

His problem was with the extra level of parsing when assigned to a variable via command substitution.

5

My Bad, try this: (ah he already said it, duh... good thing the day is over)

echo "Enter the name of the volume"
read Volume
echo "You've chosen \"$Volume\""
# remove spaces from name of Volume
uVolume=`echo "$Volume" | sed 's/ /\\\ /g'`
echo $uVolume


Enter the name of the volume
old mac hd
You've chosen "old mac hd"
old\ mac\ hd
6

ikon,

that worked. can you or the others explain the syntax for me?

i'd used:
uVolume=`echo "$Volume" | sed 's/ /\\ /g'` and got no results

you suggested:
uVolume=`echo "$Volume" | sed 's/ /\\\ /g'` and i get exactly the results i wanted.

what does that extra "\" tell the code?

7

also my thanks to cfajohnson! didn't mention that before, gents, sorry.

8

There's another way to do the same:

$ echo $myvar
asd sdd aa
$ myvar1=`echo "$myvar" | sed 's/ /\\ /g'`
$ echo $myvar1
asd sdd aa
$ myvar1=$(echo "$myvar" | sed 's/ /\\ /g')
$ echo $myvar1
asd\ sdd\ aa

For an explanation see the section 'Command Substitution' in bash's man page (assuming you're using bash).