[SOLVED] how replace string repeated pattern at his start ,linux terminal?

how replace string repeated pattern at his start ,linux terminal?

I want to edit a string that I get using regular expression in linux shell but I failed.

the thing I want to do is at the start of the string to change repeatedlly occurrence of "00" to "1"

let say : 00000120001 to 110100001 but I failed to that.

I tried:

echo 00000120001 | sed 's/^\`\<00/1/g'

but got 1000120001

Solution

Not sure you can do it with a single regex; I have a solution with juggling with the hold and pattern spaces of sed.

In one line:

sed 'h;s/[^0].*//;s/00/1/g;x;s/^0*//;x;G;s/\n//' <<< '00000120001'

With details:

sed 'h          # copy input line to hold space
     s/[^0].*// # keep only 00..0 prefix in pattern space
     s/00/1/g   # replace double 0s by 1s in pattern space
     x          # swap hold and pattern spaces (hold is now 110, pattern 00000120001
     s/^0*//    # remove 00..0 prefix from pattern space
     x          # swap hold and pattern spaces (hold is now 120001, pattern 110
     G          # append hold space to pattern space (pattern is 110\n120001)
     s/\n//'    # remove \n from pattern
<<< '00000120001'