Prepend x/ to line where x is a variable on each line

Question

I want to add $x/ from data formatted as $x-xyz (xyz is a mix of text and number to be ignored).

Example data

AB-10C
CD-02E

Output

AB/AB-10C
CD/CD-02E

How do I describe the variable as text before the hyphen? My idea is:

define $x = # dunno how to do that
## and then somehow use sed to prepend
sed -i s/$/$x/ file
# I don't know if sed can handle variables though - the above one liner is from Googling

Please advise.

Answer 1

Here's a quick and dirty awk version:

awk -F- '{print $1"/"$0}' input_file > output_file

What it does is use - as a field separator, and prints the first column (i.e. everything before the first -), then a /, then the whole original line.

A way of doing the same thing with sed would be:

sed -e 's;^\([^-]*\)\(.*\);\1/\1\2;' input_file > output_file

(but that's hardly readable.)

If you want to do it in plain bash, you can use string manipulations:

$ foo=AB-10C
$ prefix=${foo%%-*}
$ echo ${prefix}/${foo}
AB/AB-10C

Use that in a while read loop or similar if the data is coming from a file.

Answer 2

This might work for you:

echo -e "123,AB-10C,4\n567,CD-02E,8" |
sed 's|\([^,]*\)-.*|\1/&|'
123,AB/AB-10C,4
567,CD/CD-02E,8