I'm calling several unix commands and python on a python script from a qsub shell script, meant to run on a cluster. The trouble is that when the script executes, something seems to go awry in the shell, so that directories and files that exist are not found. For example, in the .out output files of qsub I see the following errors:

cd: /valid/dir/name: No such file or directory
python valid/script/name.py 
python: can't open file 'valid/script/name.py': [Errno 2] No such file or directory

so the script cannot cd into a dir that definitely exist. Similarly, calling python on a python script that definitely exists yields an error.

any idea what might be going wrong here, or how I could try to debug this?

thanks very much.