15

So I need to convert a date to a different format. With a bash pipeline, I'm taking the date from the last console login, and pulling the relevant bits out with awk, like so:

last $USER | grep console | head -1 | awk '{print $4, $5}'

Which outputs: Aug 08 ($4=Aug $5=08, in this case.)

Now, I want to take 'Aug 08' and put it into a date command to change the format to a numerical date.

Which would look something like this:

date -j -f %b\ %d Aug\ 08 +%m-%d

Outputs: 08-08

The question I have is, how do I add that to my pipeline and use the awk variables $4 and $5 where 'Aug 08' is in that date command?

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3
  • You're actually asking how to use the output from awk, not the variables, in the other command. Commented Aug 10, 2010 at 18:55
  • What version of date (and the OS, etc.)? GNU date doesn't have -j and it uses -f for reading from a file. Your command would be date -d Aug\ 08 +%m-%d Commented Aug 10, 2010 at 20:43
  • Not sure of the exact version number -- doesn't have any sort of --version output. It's a BSD build on Mac OSX, so I put together the date options based on the man page on OS X 10.6. Only intending to run the script on mac clients, but thanks for the info; it'll be useful should I need to do something similar on Linux. Commented Aug 11, 2010 at 0:05

4 Answers 4

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19

You just need to use command substitution:

date ... $(last $USER | ... | awk '...') ...

Bash will evaluate the command/pipeline inside the $(...) and place the result there.

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6

Get awk to call date:

... | awk '{system("date -j -f %b\ %d \"" $4 $5 "\" +%b-%d")}'

Or use process substitution to retrieve the output from awk:

date -j -f %b\ %d "$(... | awk '{print $4, $5}')" +%b-%d
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0

Using back ticks should work to get the output of your long pipeline into date.

date -j -f %b\ %d \`last $USER | grep console | head -1 | awk '{print $4, $5}'\` +%b-%d
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1 Comment

It may not matter in this case, but in general it's far better to use $(...) than backticks. It can be nested.
-1

I'm guessing you already tried this?

last $USER | grep console | head -1 | awk | date -j -f %b\ %d $4 $5 +%b-%d
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1 Comment

This does not work. awk requires parameters, and it's output is not routed to date's parameters

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