bash relative pathing for writing files

Say you have a process that needs to run and writes it logs relative to where it runs.

As a tiny example here is a python program that writes a file using a relative path (the filename is /tmp/cool.py)

outf = open("./dbg.txt","w")
outf.write("hey\n")
outf.close()

If you want to invoke that process from BASH then you have to be careful.

The file dbg.txt will be written relative to your working directory.

So in the example below the dbg.txt file is written in your home directory.

agcc@LAPTOP-BT02BD1T:~$ pwd
/home/agcc
agcc@LAPTOP-BT02BD1T:~$ python /tmp/cool.py
agcc@LAPTOP-BT02BD1T:~$ ls dbg.txt
dbg.txt

That is probably not what you wanted to do. More than likely you needed to change your working directory and then run the python script.

A really great tool to do that is subshell. In BASH that is parens around the commands.

Below I run the set of commands in a subshell. In the new subshell I change to a different directory and execute the python script then verify the file is present. I also printed my working directory.

Finally I executed an ls in my top shell (no longer in a subshell) and there is no file written in that directory.

agcc@LAPTOP-BT02BD1T:~$ (cd /tmp && python cool.py && ls dbg.txt && pwd)
dbg.txt
/tmp
agcc@LAPTOP-BT02BD1T:~$ pwd
/home/agcc
agcc@LAPTOP-BT02BD1T:~$ ls dbg.txt
ls: cannot access 'dbg.txt': No such file or directory