How to rotate enumerated filenames similar to logrotate?

Question

I have a couple of files, let's say map-0.jpg (newest), map-1.jpg, map-2.jpg, ..., map-9.jpg (oldest). Now my cronjob downloads a new picture from the internet and should save it as map-0.jpg. All other files, however, should be newly enumerated (0 -> 1, 1 -> 2, and so on). Number 9, in my case, can be discarded.

Is there a handy bash-command that enumerates my files similar as logrotate does?

Thanks for help!

Solution

you can use logrotate with some restrictions.

create a rotatemap.conf:

/path/to/map.jpg {
  rotate 9
}

then run logrotate from your cronjob like this:

logrotate -f -s /path.to/rotatemap.state /path/to/rotatemap.conf

this will rename the file map.jpg to map.jpg.1 and will delete the old map.jpg.9 if it exists.

the restrictions:

• just about every path has to be hardcoded.
• the number in the rotated files are always at the end of the filename. at least i found no way to change this.

read the fine manual of logrotate (man logrotate) for more information.

Comments

[André]

Thank you very much for your answer! I solved this by using 8x mv-commands (mv 1.jpg 0.jpg, mv 2.jpg 1.jpg) in my Bash-cronjob-script. This is very simple and uses 8 lines for 9 files (renaming 8 and discarding 1 files). Well, I thought there would be a more elegant way. However, I will study your script; maybe it inspires me in the future, when I will have similar problems :)

[André]

Thank you, I think I will do it that way. The hardcoding thing is okay, as I have to use the full path in my cronjob-table (crontab -e) anyway. The rotated files will be served by Apache, which I can convince to add the appropiate Content-type-header!

[glenn jackman]

Here's 2 lines for 9 files.

[André]

Well, that's a nice one-/two-liner that I expected ^^

[André]

It doesn't matter if I keep 9, 10 or 20 files... The most interesting part is the $((i+1)) thing for me. I know that $() is a sub-command. So (i+1) will be calculated, but why don't you use "echo"? Or is the bash intelligent enough to know what I want? And I think you forgot the dollar-sign in the subcommand, didn't you? :)

[glenn jackman]

$( ... ) and $(( ... )) are two separate syntaxes in bash. The former is command substitution; the latter is arithmetic evaluation.

[gies0r]

What is rotatemap.state?