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I have two data files with date stamps in different formats (as text in the file contents).  I wish to compare the two dates and print the variable from one file to another according to date in a shell script.  I have a script in MATLAB, but I’d like to do it in a shell script.  In one file, the date format is 2017-01-01 12:00:00. In the other file it is 20170101 1200. For a variable I want to compare it with date in file1 and if it matches print variable as column in file1 from file2.

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    Welcome to U&L, please take the tour to see how to ask good questions. As a rule you need to include samples of your input files, the code you have tried, the output you got and the output you want. If you update your question with these then people will be able to give better help so ... please add this detail.
    – bu5hman
    Commented Jul 3, 2020 at 7:35
  • Read man date, and use the --date= and --format= options to convert both dates to "seconds since the epoch".
    – waltinator
    Commented Jul 3, 2020 at 14:54
  • @waltinator, what version of date has a --format option? Commented Jul 3, 2020 at 17:45
  • As bu5hman says: (1) Show samples of your input files. Is file1 20 characters long (e.g., 2017-01-01 12:00:00 and a newline, and nothing else)? Is file2 14 characters long (e.g., 20170101 1200 and a newline, and nothing else)? If not, you haven't shown us samples of your input files.  (2) Show what output you want/expect.  (3) Show us your MATLAB script. (P.S. Does it work the way you want?)  (4) Try to do this in a shell script, and show us your best attempt. … … … … … … … … … … … … … Please do not respond in comments; edit your question to make it clearer and more complete. Commented Jul 4, 2020 at 0:33

1 Answer 1

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You can do this in plain bash with parameter substitution:

dateA='2017-01-01 12:00:00'
dateB='20170101 1200'

tmpA=${dateA//[-:]/}   # remove hyphens and colons
# next expansion excludes last 2 characters
[[ "${tmpA:0:-2}" == "$dateB" ]] && echo same || echo different
same

Older bash versions don't support negative lengths, but you can use ${tmpA:0:${#tmpA}-2}

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