Can you convert a date to yyyy/mm/dd using sed?

user_11136877 0
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I have a utility that outputs the software expiration date into a text file called expiration. The file has one line and it is below:

node_software_expiration_date Sat Jul 6 23:59:59 2025

I'd like to replace the text in the file to read:

node_software_expiration_date 20250706

I'm using sed to replace the current text. I can't edit the utility. Open to other options.

I'm running this in cron:

./export_expiration && sed -e 's/Software Expiration/node_software_expiration_date /' > expiration

sed awk bash
6 Answers

You can use date --date=STRING to parse pretty much any free-form date string (it accepts many different syntaxes, so is pretty robust), and then +FMT to output whatever format you want. The main difficultly with your example is replacing the file in place. Something like:

read prefix date < expiration
echo $prefix $(date --date="$date" +%Y%m%d) > expiration

should do the trick in a shell script. Note that if the input date string includes a time close to midnight in some other timezone, this may end up adjusting the day by one, which might actually be what you want.

user_164060

Using any awk in any shell on every Unix box:

$ awk '{printf "%s %04d%02d%02d\n", $1, $6, (index("JanFebMarAprMayJunJulAugSepOctNovDec",$3)+2)/3, $4}' file
node_software_expiration_date 20250706
user_17450010

Using GNU sed

$ sed -i "s/\([^ ]* \)\(.*\)/echo \1\$(date -d '\2' +'%Y%m%d')/e" input_file
$ cat input_file
node_software_expiration_date 20250706
user_163721090

This might work for you (GNU sed):

sed -E 's/$/\nJan01Feb02Mar03Apr04May05Jun06Jul07Aug08Sep09Oct10Nov11Dec12/
        s/ (. ..:..:.. )/ 0\1/
        s/... (...) (..) ..:..:.. (....)\n.*\1(..).*/\3\4\2/' file

Append a lookup table.

Cater for the first nine days of a month.

Pattern match, forming the result in the desired format.

user_9674920 
$ awk '{n=$1; $1=""; printf "%s ",n; print |"date -d \"" $0 "\" +%Y%m%d"} file
node_software_expiration_date 20250706
user_41778280

I suggest following simple if somewhat long GNU sed solution, let file.txt content be node_software_expiration_date Sat Jul 6 23:59:59 2025 then

sed -e 's/ \([0-9]\) / 0\1 /g' -e 's/\([^ ]*\) \([^ ]*\) \([^ ]*\) \([^ ]*\) \([^ ]*\)$/\5 \2 \3/' -e 's/ Jan /01/' -e 's/ Feb /02/' -e 's/ Mar /03/' -e 's/ Apr /04/' -e 's/ May /05/' -e 's/ Jun /06/' -e 's/ Jul /07/' -e 's/ Aug /08/' -e 's/ Sep /09/' -e 's/ Oct /10/' -e 's/ Nov /11/' -e 's/ Dec /12/' file.txt

gives output

node_software_expiration_date 20250706

Explanation: firstly pad single digit (digit surrounded with spaces) using 0 to width of 2. Then extract and change order of fields to that of desired format: that is year, month, day. Finally replace callsign of month and surrounding spaces with zero-padded number.

(tested in GNU sed 4.2.2)

user_107859750
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