find and replace in a file using awk or SED

Hi

I want to create a script which reads string1 from file1 searches that string1 in file2 and then replaces it with string2 which also there in file1.
Actually we are doing a migration and in this i need to replace lot server names and with new names and i want to take read old server name from a file search it in the file and then replace it with new server name.
Please help me .

Thanks,
krish

both sed and awk can do the job. i prefer sed.
supposed list1 has the format: oldname#newname (you gave no exemple)
i suggest:
a sed cmd translating the list1 in a sed cmd file, exec it, let have a look


this will translate old#new to /old/s//new/g
which is a sed statement replacing all occ of 'old' by 'new'
now executing
sed -f sedcmd file2 > newserversnames
does the job.
remember, sed has limits, i believe (not sure) 200 cmds a file
so if your file1 if >200 lines, after the first sed you must split 'sedcmd'
and use a cascade
sed -f sed1 file1¦sed -f sed2¦sed -f sed3 ..... >output
see man pages of 'split' and 'sed'