Please can anybody help with a simply-stated sed problem? I realise this is
not Cygwin-specific, but it is Cygwin-relevant because it is required in
order to write a script to mount a portable Cygwin system on any host
machine, so I hope it's all right to ask for help here.
The problem reduces to:
In any string (eg "xaaabababbbxaabbbabx") remove all instances of "ab" and
keep on doing this as long as you can.
Do it once:
echo xaaabababbbxaabbbabx | sed 's/ab//g'
xaabbxabbx
The essential issue is that that removal of all instances of "ab" has
created new instances of "ab" in the reduced string, so it needs to be done
again:
echo xaaabababbbxaabbbabx | sed 's/ab//g' | sed 's/ab//g'
xabxbx
and it needs to be done a 3rd time to reach the irreducible string
echo xaaabababbbxaabbbabx | sed 's/ab//g' | sed 's/ab//g' | sed
's/ab//g'
xxbx
Different initial strings might need more passes through sed, and it's not
possible to forecast how many passes will be needed (well, it is, but only
by a complex counting algorithm). Is there a way with a single sed command
echo xaaabababbbxaabbbabx REPEAT{| sed 's/ab//g'}
that I can "repeat the pipe as many times as possible" and then stop?
Don't know whether this is obvious/ simple/ difficult/ possible/ or any of
these: thank you.
Fergus
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