Question

I need to write a shell script to run as a cron task, or preferably on creation of a file in a certain folder.

I have an incoming and an outgoing folder (they will be used to log mail). There will be files created with codes as follows…

bmo-001-012-dfd-11 for outgoing and 012-dfd-003-11 for incoming. I need to filter the project/client code (012-dfd) and then place it in a folder in the specific project folder.

Project folders are located in /projects and follow the format 012-dfd. I need to create symbolic links inside the incoming or outgoing folders of the projects, that leads to the correct file in the general incoming and outgoing folders.

/incoming/012-dfd-003-11.pdf -> /projects/012-dfd/incoming/012-dfd-003-11.pdf
/outgoing/bmo-001-012-dfd-11.pdf -> /projects/012-dfd/outgoing/bmo-001-012-dfd-11.pdf

So my questions

1. How would I make my script run when a file is added to either incoming or outgoing folder
   1. Additionally, is there any associated disadvantages with running upon file modification compared with running as cron task every 5 mins
2. How would I get the filename of recent (since script last run) files
3. How would I extract the code from the filename
4. How would I use the code to create a symlink in the desired folder

---

EDIT: What I ended up doing…

while inotifywait outgoing; do find -L . -type l -delete; ls outgoing | php -R '
if(
    preg_match("/^\w{3}-\d{3}-(\d{3}-\w{3})-\d{2}(.+)$/", $argn, $m)
    && $m[1] && (file_exists("projects/$m[1]/outgoing/$argn") != TRUE)
){
    `ln -s $(pwd)/outgoing/$argn projects/$m[1]/outgoing/$argn;`;
}
'; done;

This works quite well – cleaning up deleted symlinks also (with find -L . -type l -delete) but I would prefer to do it without the overhead of calling php. I just don’t know bash well enough yet.

Answer 1

Some near-answers for your task breakdown:

1. On linux, use inotify, possibly through one of its command-line tools, or script language bindings.
2. See above

3. Assuming the project name can be extracted thinking positionally from your examples (meaning not only does the project name follows a strict 7-character format, but what precedes it in the outgoing file also does):

   echo `basename /incoming/012-dfd-003-11.pdf` | cut -c 1-7
   012-dfd
   echo `basename /outgoing/bmo-001-012-dfd-11.pdf`| cut -c 9-15
   012-dfd
   

4. • mkdir -p /projects/$i/incoming/ creates directory /projects/012-dfd/incoming/ if i = 012-dfd,
   • ln -s /incoming/foo /projects/$i/incoming/foo creates a symbolic link from the latter argument, to the preexisting, former file /incoming/foo.