I have the following command that I'm trying to tweak:

 stat -c %y test.txt | sed 's/^\([0-9\-]*\)/\1/'

This returns the following information:

 2016-08-03 14:52:24.000000000

I need to tweak this so that it excludes the ".000000000". I've tried a few different options but can't seem to get it right. Ultimately, I need to take the time stamp that I extract from the above command, and echo it as the first line into the file.

I have this command as an example that seems to correctly add a new line to the top of the file:

   sed -i '1s/^/this should be a date\n/' test.txt

How do I combine the two commands?

sed -i "1i$(stat -c %y test.txt | sed -r 's/\.[0-9]+ / /')" test.txt
| improve this answer | |
  • Florian your example includes the trailing 00000 in the timestamp – Happydevdays Aug 3 '16 at 15:39
  • @Happydevdays: I get something like 2016-08-03 17:41:42 +0200. Maybe it's caused by the locales. Try sed -r 's/\.[0-9]+//' – Florian Diesch Aug 3 '16 at 15:47

Like so:

( stat -c %y test_file.txt | awk -F '.' '{print $1}' ; cat test_file.txt  ) > /tmp/temp_file && mv /tmp/temp_file test_file.txt

Here's a small demo:

$> echo "Hello World" > test_file.txt
$> ( stat -c %y test_file.txt | awk -F '.' '{print $1}' ; cat test_file.txt  ) > /tmp/temp_file &&                       
> mv /tmp/temp_file test_file.txt
$> cat test_file.txt                                                                                                     
2016-08-03 09:24:27
Hello World


  • We get timestamp and file contents in subshell , signified by parenthesis (...)
  • stat -c %y test_file.txt | awk -F '.' '{print $1}' trimps timestamp
  • cat test_file.txt reads file contents.
  • The resulting text is timestamp plus whatever was in file, is being redirected to /tmp/temp_file
  • Finally we replace original file with contents of /tmp/temp_file
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  • Thanks so much for this helpful post. I accepted the other answer only because it's a little more concise. – Happydevdays Aug 3 '16 at 17:06

How about using ed instead of sed?

$ ed -s test.txt << EOF
0r !stat -c \%y %
1 s/\.[0-9]*//

This says:

  • read the output of command stat -c \%y % and insert it at position 0 in the buffer i.e. before the first line. Note that in ed, an unescaped % is shorthand for the current file.
  • on this (now first) line, substitute nothing in place of the decimal period and following digits
  • write the result back to the file and quit

The -s is optional - it just prevents ed from outputing line counts. If stat appends a timezone offset in your locale / timezone, and you wish to remove that as well, then you can modify the s command to remove the period and everything following it e.g. s/\..*//

It's also possible to use ed in a one-liner taking its commands from standard input using echo or printf, although it's a little tricky to get the escaping right:

printf '0r !stat -c \%%y %%\n1 s/\.[0-9]*//\nw\nq' | ed -s test.txt
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