A way to check stdin for value?

[bigdmy]

I'm troubleshooting a script written years ago by another developer. Roughly the script does the following:

Create an empty file

cat > new_file

Process new_file that now has something in it


The script has been working fine with one exception. If the stdin is empty, the script hangs at "cat > new_file". Is there a way to check stdin for value before attempting the cat or a way past the cat if stdin is empty?

Thanks in advance

 

[cruel]

Why can not you switch to something like "touch new_file", or is there something I am missing?

 

[vgersh99]

you can simply do to create an empty file:
> new_file

vlad
+----------------------------+
| #include<disclaimer.h> |
+----------------------------+

 

[bigdmy]

Thanks for taking the time to reply.

The problem is not with the empty file. The script does create an emty file based on date/time, etc. Once the 0 byte file is created on the disk, the next step is to put something into the new file, hence &quot;cat > new_file&quot;. The something that we are attempting to &quot;cat&quot; into the new_file from stdin is report output generated from a 4gl program. For the most part this process works ok as long as there is actually data in stdin. However, once in a while a user runs a report of some type with criteria that produces an empty report. If this happens, stdin is empty (or appears to be empty) and the script hangs at the &quot;cat&quot;. What I'm interested in is a way to prevent the script from hanging. I thought there might be a way to check if stdin has data in it and code around the cat to exit the script nicely if stdin is empty.

Thanks again for your help.

 

[cruel]

I have been using ksh, but there should be many way to do what you want.
1) use an condition check like if, ! -s, which means its size is zero.
2) could also use a simple command like ls to check if file is empty
3) use awk or sed to see if anything between the beginning and ending

if returns a positive response, then go ahead with your cat command. let me know if you need more specifics on those.