There are almost certainly much simpler ways to do what you're trying to do, but we need to know what operating system and shell you're using to be able to suggest a solution that will work in your environment. Whenever you start a new thread in UNIX for Beginners Questions & Answers forum, it always helps us help you if you tell us what operating system and shell you're using!

I note that you're trying to use awk's gsub() function which will replace all occurrences of file with newfile. And I note that none of your filenames contains more than one occurrence of that string. If that string does occur more than once in a filename, do you really want to replace all of them? Or, do you just want to change the first occurrence?

The error you're getting is because you haven't quoted the awk script operand and the shell is seeing the parentheses on the call to gsub() as an attempt to invoke a sub-shell at a spot where a sub-shell is not valid.

If you fix that and you ever try passing a filename to that script that does not contain the string file, the mv command for that file will fail because the variable t will be set to an empty string. If you make sure that your awk script will always return the original filename if no occurrences of the string file were found, you would end up trying to issue a command similar to:

Code:

mv a.txt a.txt

which will be a relatively slow no-op; but at least it won't cause your script to issue diagnostics for missing operands.

The command substitution you're using is an obsolescent form (unless you're using a pure Bourne shell from the 1970's. And, there is no reason to invoke a sub-shell in your command substitution.

Does the operating system you're using include a utility named rename?