Suppose I get the following result after doing a grep "emailed"

/home/John/logs/2013-07-10.171222-0400EDT.html:I have emailed Mark. Thanks

I want to extract the date from this so that my output looks like -

2013-07-10:I have emailed Mark. Thanks

How can I do this using any one of the GNU tools? In particular, I want to pipe the output of grep to the tool. I suppose that sed may be the tool that does this, but I'm not sure how.



$ <grep-command> | sed -r 's|^.*/([0-9]{4}-[0-9]{2}-[0-9]{2})[^:]*:(.*)|\1:\2|'

... ought to work. In detail:

  1. -r tells sed to use extended regular expressions.

  2. s|a(b)c(d)|\1:\2| says "match a then b then c then d, and replace the whole thing with b:d (the first and second parenthesized items, separated by a :", where a .. d are:

    a. ^.*/ - everything (.*) from the beginning of the line (^) to a / character (which is why we're using | instead of / to separate the clauses of the s command).

    b. [0-9]{4}-[0-9]{2}-[0-9]{2} - a digit ([0-9]) four times ({4}), followed by a -, followed by a digit twice, etc.

    c. [^:]*: - anything that isn't a : ([^:]*), followed by a :.

    d. .* - everything else.

  • Wow, that's amazing. Could you please explain what your above command is doing? – CodeBlue Jul 23 '13 at 21:05
  • Or better yet sed -n -r '/emailed/s/|...|p to get rid of the grep altogether. – tripleee Jul 24 '13 at 5:21

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