Shell Programming and Scripting

True, but if you look closely, you can see that the first file has a leading space in its name.

Hi Rudic Thank you for explanation.I understood your logic except the below.

As mentioned We will have multiple files in a folder with different file names we should pick only the files which start with abc_*_*.dat which came with in last 3 days.Can you please tell how we are doing this?

And also filetimestamp and the $THREEDAYSAGO values/format is fifferent .how we are comparing both? in if condition?Can you explain with example.

Filenames in folder:

Code:

1)abc_20171204.052389.dat
2)abc_20171204.052428.dat
3)def_20171204.052440.dat
4)ghf_20171204.054340.dat

Code:

C:

for file in *_*_*.dat
do
   FILESTAMP=${file#*_}
   FILESTAMP=${FILESTAMP%_*}

Moderator's Comments:

Please use CODE tags as required by forum rules! And, DON'T modify posts (here: #1) if others already referenced it, pulling the rug from under their feet!

My first and most important advice is that you apply utmost care when creating a post - watch your spelling, upper / lower case, punctuation, and data accuracy. Why should anybody care more for your posts than you do? Why should anybody want to guess what your problems are?
In your post#9:
- what is the C: for?
- you write "files which start with abc_*_*.dat" but post sample files like ghf_20171204.054340.dat - neither the abc nor the second _ appears; so: which one is valid? The code doesn't work with a wrong pattern.
- with "filetimestamp" you mean FILESTAMP? The latter is not directly compared to $THREEDAYSAGO but converted to seconds before the compare.

I agree.Below are the file names we receive in folder.

Filename in a folder:

Code:

abc_20171204.052389.dat
abc_20171204.052428.dat
def_20171204.052440.dat
ghf_20171204.054340.dat

Can you please explain how we are getting the 'FILESTAMP' from above filenames and converting into seconds?


and what will be the result for below code?

Code:

for file in *_*_*.dat
do
   FILESTAMP=${file#*_}
   FILESTAMP=${FILESTAMP%_*}

The result for the cited code is unpredictable as it depends on the number of files in that directory containing at least one _ character (disregarding the .dat ending). As said in post#10, the pattern does NOT match your target files.

Look into your shell's (which version you fail to mention, btw) man page for "Parameter expansion; Remove matching prefix / suffix pattern." to see how ${file#*_} and ${FILESTAMP%_*} are used to extract the time stamp from the file names. Also, use echo in the loop to print out the intermediate states of the extraction.
In post#6 you see date -d $FILESTAMP +'%s' used to convert the time stamp into epoch seconds for the comparison.

Hopefully this will be my last question .

1)If we have multiple set of files in a folder like below, how we are looping each file for doing comparison?

Code:

abc_20171204.052389.dat
abc_20171203.052428.dat
abc_20171202.052628.dat

2)for looping are we doing below logic in script?

Code:

for file in *_*_*.dat
do
   FILESTAMP=${file#*_}
   FILESTAMP=${FILESTAMP%_*}

3)if so can you please explain the above code with an example?

In all of your early posts you said that files were named using the pattern abc_YYYYMMDD_hhmmss.dat and the code that RudiC suggested processes the files that match the pattern you supplied.

When you then try running the code he suggested in a directory that doesn't have any files that match that pattern, the code won't find any files that match the pattern you told us all that you wanted to process. This is a classic example of what happens when you supply sample data that doesn't match your real data.

Feel free to modify the code RudiC suggested to match the format of the real filenames you are trying to process. Do not blame RudiC for supplying code that looked for what you said should be looked for when no files in that format are present.

To make the code match the latest sample names you have provided, you'll need to change the filename matching pattern in the for statement and change the parameter expansion that is used to extract the date from the expansion of the shell FILESTAMP variable.