I'm new in this shell scripting subject, I´m looking forward for someone to give me a hint or advice as to how to tackle my requirement, which is as follows:
We have a Linux process that runs periodically every day, this process dumps a text file with always the same name overwriting the previous one (information is incrementally added). What I need to accomplish is to rename this file as soon as possible once is generated, following the following nomenclature:
The year, month and day has to be fetched from the first line of the file content, here is an example:
Code:
M16540035421004411262012N 11 SAMPLE WORD SAMPLE WORD
The year, date and month will always be found in a fixed position from this first line (position 17 to 24), which in this example is as follows:
Code:
11262012
This date is expressed in Month-Day-Year format, and my requirement needs it to be [year][month][day]
Another thing that I need to track is if original file is currently being used, since I dont want to rename the file in the middle of the generation process.
At the end, filename should be:
Code:
Fixed description-Fixed numeric code-20121126.txt
Kindly requesting your help with my requirement.
Many many thanks in advanced for any help you can provide.
Last edited by Don Cragun; 06-20-2014 at 05:50 PM..
Reason: Change FONT tags to CODE tags.
Longhand from the CLI only, OSX 10.7.5, default bash terminal...
This makes assumptions that the first field is constant length.
If not then a slightly more difficult approach is needed...
Code:
Last login: Fri Jun 20 18:11:46 on console
AMIGA:barrywalker~> echo 'M16540035421004411262012N 11 SAMPLE WORD SAMPLE WORD' > /tmp/sample
AMIGA:barrywalker~> cat < /tmp/sample
M16540035421004411262012N 11 SAMPLE WORD SAMPLE WORD
AMIGA:barrywalker~> text=$(cat < /tmp/sample)
AMIGA:barrywalker~> echo "$text"
M16540035421004411262012N 11 SAMPLE WORD SAMPLE WORD
AMIGA:barrywalker~> text="${text:20:4}${text:16:4}"
AMIGA:barrywalker~> echo "$text"
20121126
AMIGA:barrywalker~> # REMEMBER TO BACKUP YOUR ORIGINAL FILE.
AMIGA:barrywalker~> mv /tmp/sample /tmp/"Fixed description-Fixed numeric code-$text.txt"
AMIGA:barrywalker~> ls -l /tmp/
total 24
-rw-r----- 1 root _lp 1193 20 Jun 18:11 0001653a4f82c
-rw-r----- 1 root _lp 1234 20 Jun 18:11 0001653a7018c
-rw-r--r-- 1 barrywalker wheel 60 20 Jun 20:29 Fixed description-Fixed numeric code-20121126.txt
drwx------ 3 barrywalker wheel 102 20 Jun 18:11 launch-B5kUmu
drwx------ 3 barrywalker wheel 102 20 Jun 18:11 launch-UEgXYb
drwx------ 3 barrywalker wheel 102 20 Jun 18:11 launch-ce6iKr
drwx------ 3 barrywalker wheel 102 20 Jun 18:11 launch-gfvxa4
drwx------ 3 barrywalker wheel 102 20 Jun 18:11 launchd-130.7TVN3n
AMIGA:barrywalker~> cat < /tmp/'Fixed description-Fixed numeric code-20121126.txt'
M16540035421004411262012N 11 SAMPLE WORD SAMPLE WORD
AMIGA:barrywalker~> _
EDIT:
Forgot about the file locking bit, research:-
Code:
man fuser
Last edited by wisecracker; 06-20-2014 at 04:51 PM..
Nothing has been said about the size of the input file, nor about how the process that updates this file is written.
If the file size is more than a few lines (and especially if it could be large), reading the entire contents of the file into a variable to get a few characters out of the 1st line is wasting time and space. I would strongly suggest using:
If the process that is writing to this file opens the file once and writes data to the file using that single file descriptor, you don't need to worry about locking at all. Renaming the file (as long as you don't move it to a different file system) won't affect the file descriptor being used by the process that is adding data to the file. All of the data for an update will be appended to the file you're moving or to a new file after you've moved it.
But, if the program that is updating the file is opening the file multiple times, then you do need to make sure that you don't move the file while the updater is running. The fuser utility probably won't help you in the case where it matters. You'll need a way to synchronize file updates with file renames and that will require more information than you have provided. It is easy to create a lock file, but both the updater and the mover need to agree on the lock and cooperate with each other to make that work. If just one of the two parties tries to guess whether or not the other one is active; eventually something will go wrong.
Are you responsible for both the updater and this code to rename the file?
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06-20-2014
Help with file rename script