cat >>

hi cat a.txt >> b.txt will append a.txt to the end of b.txt. But how can i replace a.txt to b.txt start at the beginning?

for example: if a.txt contain 'abc' and b.txt contain '123456' i want 'abc456' in b.txt

thanks from Peter ( This e-mail address is being protected from spam bots, you need JavaScript enabled to view it )

I don't think you can do this from the shell. You can do it from (at least) C or Perl, though:

fernando@linx4 tmp $ cat a abc fernando@linx4 tmp $ cat b 123456 fernando@linx4 tmp $ dd if=a of=b bs=1 count=3 conv=notrunc 3+0 records in 3+0 records out fernando@linx4 tmp $ cat b

i dunno about dd, looks like magic to me. most folks will use awk or sed for the stated purpose. try the man pages.

... that's the beauty of *nix ... there are multiple ways to skin a 'cat' (pun intended

... hehehehehehhee. i can NEVER figure this out. every time i see the command 'wc', i think of the expression 'water closet'

thanks foor all the reply. When i echo '#f1', nothing come out. What does the #f1 mean?

thank you from Peter ( This e-mail address is being protected from spam bots, you need JavaScript enabled to view it )

${#f1} is the length of the variable f1 ${f2} is the value of the variable f2, starting from position x

So,

${f2:${#f1}} is the value of the variable f2, starting from the position of the last character in f1.

THANK YOU