A simple variable subst is not working

Shell Programming and Scripting
1

Hi

what i want:
listing files in a special range

ls -lrt 20120601{05..06}*
 ...
 -rw-rw-r-- 1 imp imp 279  1. Jun 07:51 201206010550
 -rw-rw-r-- 1 imp imp 279  1. Jun 07:01 201206010600
 -rw-rw-r-- 1 imp imp 279  1. Jun 07:11 201206010610
 -rw-rw-r-- 1 imp imp 279  1. Jun 07:21 201206010620
 -rw-rw-r-- 1 imp imp 279  1. Jun 07:31 201206010630
 -rw-rw-r-- 1 imp imp 279  1. Jun 07:41 201206010640
 -rw-rw-r-- 1 imp imp 279  1. Jun 07:51 201206010650

.. setting the command like this, it is working properly.

If i subst one value by a variable or a command...

M=05
ls -lrt 20120601{$M..06}*
"note"
ls: no access to 20120601{05..06}* : cant find file or directory.
.. with the command ..
ls -lrt 20120601{`date +%m`..06}ls -lrt 20120601{`date --date="9 days ago" +%m`..06}
ls: no access to20120601{05..06}*cant find file or directory.

It seems to me, that the brackets are still there ..
A colleague gave me a first hint ..

ls -lrt `eval echo 20120601{$M..06}*`

Can someone help me, how to do it... more elegant and especially with the subst. commands.

Thanks in advance
IMPe

2

Actually the solution your colleague gave you is correct. The reason is that there is a certain step-by-step procedure which the shell follows when evaluating commands. Your code assumed that these steps are interchangeable, but they aren't.

This is where "eval" enters the picture: eval tells the shell to restart this process at step one and so - by evaluating your commandline in fact twice - it is possible to first evaluate "$M" and only then evaluate "{05..06}".

You might want to read this thread for a more detailed explanation. The symptom there was different but the problem was the same.

I hope this helps.

bakunin

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