How to parse a string efficiently

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# 1  
Old 05-13-2008
How to parse a string efficiently

I am new to the boards and to shell programming and have a requirement to name new files received with a unique sequence number. I need to look at a particular file pattern that exists and then to increment a sequence by 1 and write the new file.

Example of file names and sequence #


the sequence is a 6 digit right justified 0 filled number attached to the date - 20080501000001.dat, but may be the 4th, 5th, 6th or 7th token of the filename.

I have a script that creates the new files, but I am having trouble with how to efficiently extract the sequence number in order to increment it by 1 for a given file pattern and date and then write the new file.

Any help would be appreciated and I am trying to stay with shell or sed or awk as I do not have access to perl.


# 2  
Old 05-13-2008
one way:

echo ${file%%.dat} | read seq
len=`expr length $seq`
let start=$len-14
seq=`expr $seq $start 14`
typeset -i num
echo ${seq##????????} | read num
echo $num

Last edited by jim mcnamara; 05-13-2008 at 12:49 PM..
# 3  
Old 05-13-2008

Exactly what I needed - thanks!
# 4  
Old 05-13-2008

Could you please breakdown how this works? I am changing up how I return the filenames and it is now not working. I am using an ls -a and get a fully qualified path, but your code above does not seem to handle this.


# 5  
Old 05-13-2008
I just used your example filenames.

# this line was file="20080501000001.dat"
ls -rt  part1_*`date "+%Y%m%d`*.dat | tail -1 read file

This find the last occurrence of the file - ie. the highest sequence number for a file received today. the variable "file" is just the filename with the newsest sequence embedded in it.
Assuming I got your requirements.
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