Shell Programming and Scripting

Better:

Code:

sed ':L; s/,,/,0,/g; tL; s/,$/,0/' file

manas_ranjan, in case you are interested: the reason why your initial solution didn't work and why RudiC's second solution does is because replacements - regardless of sed or awk - are not done consecutively but simultaneously. Consider the following example string:

Code:

,,,

By your regexp you replace the (marked blue) part by the (marked red) replacement:

Code:

Before: ",,,"      After: ",0,,"

The resulting ",," will not be replaced because for this to work the whole line would have to be re-evaluated. But during the first pass only "," remains to be evaluated and you asked for only ",," to be replaced, not ",".

RudiC's solution worked because it sets up a loop: after replacing the first occurrence the string looks:

Code:

,0,,

Then, the command tL is executed. "t" will branch to the marker "L" (which is at the beginning: :L) if the last "s/..."-command did indeed replace something. If not, it does nothing. Because RudiC has used the "g"-option only two passes at max are necessary:

Code:

String: ",,,,,,,,,,,,,,,,"
pass 1: ",0,,0,,0,,0,,0,,0,,0,,0," -> return to "L" marker
pass 2: ",0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,"  -> return to "L" marker
pass 3: nothing changed, end of loop ("," at the end is changed by the last substitution to ",0")

I hope this helps.

bakunin

If you would like a Perl alternative:

Code:

perl -pe 's/,(?=,)/,0/g and s/,$//' manas_ranjan.file