Shell Programming and Scripting

I need to replace anything immediately after the pattern "standard01/" in a file with the value of a variable
I don't know the length of the characters stored in that variable. - that might vary.
I know there is some string after the pattern "standard01/", i don't know the what the string is or the length of it. but i know after that string following "standard01/", there is blank space and after that a word called "buf" in that file

So, the string following the pattern "standard01/" for example looks like
"special_previlege_datetime.lst" followed by a space and then a string begins with "buf" - when in the process of replacing the value of the variable right after the above pattern "standard01/" - i should not start overwriting the next string "buf"
- in other words i should try to replace/write the value of the variable starting
immediately after "standard01/" and before the next word "buf" begins.

Please provide your advice.
Your help is greatly apprecitaed.
Thanks

a way is: sed -i 's/standard01\/ .* buf/standard01\/ NUMBER buf/g' file.in
if you guarantee that all characters between the standard01/ and buf are digits, you can use: sed -i 's/standard01\/ [0-9]* buf/standard01\/ NUMBER buf/g' file.in