So I have an if loop which iterates through all files of form cluster_*

The problem is, if there are not files that match that pattern, my script trips up. What I'd like to do is, test whether any files match the pattern cluster_* and if so, continue.

What I was thinking is:

if [ -f cluster_* ] ; then
...
...
fi

but since it does not recognize cluster_* as a pattern, it searches exactly cluster_* . Any suggestions?

Maybe I don't get the exact problem. Are you trying to see if there are files whose name begins with "cluster_" inside specific directories? Why don't you use ls, if this is the case?

Maybe I don't get the exact problem. Are you trying to see if there are files whose name begins with "cluster_" inside specific directories? Why don't you use ls, if this is the case?

Yes, downstream in my script, I use the files in a for loop:

for zzCLUSTERS in cluster_*; do

cat "${zzCLUSTERS}" | tr '/' ' ' | awk '{print $1}' | sort | uniq | cat > reads."${zzCLUSTERS}"

done

But if there are no matches for cluster_*, it enters cluster_\* into ${zzCLUSTERS} , which throws off my script which is why I wanted this test.

Would you mind explaining the syntax to me?

if ls cluster_* > /dev/null 2>&1

I'm use to seeing if statements as

if [ ] ;

and > as a redirect

what does /dev/null mean and what does

2>&1 mean?

Ok. The if statement can be used to test an expression enclosed in square bracket or to test the result of a command, as in my example. You know about the exit code of a command? Any command in linux has an exit code, which is usually 0 if the command had success, a value different than 0 (in most cases 1) if the command failed.

You can retrieve the exit code explicitly using
where $? is a special variable storing the exit code of the previous command.

The if ls statement test the result of the ls command based on its exit code: if it is successful the commands inside the if/then block are executed, otherwise they are skipped. The
just redirect the standard output to /dev/null, which is a sort of black hole in unix systems. This prevent the output to be shown in the terminal, since you're not really intersted to visualize the list of files. The 2>&1 just redirect the standard error to the standard output, so that even the error message (when no file is found) is not displayed. Hope it is clear now.

In this case filename expansion for noon-exist filenames will be empty string