Change date format with sed or awk in file

Question

I have file which has following format

----------------------------------------
  Name: cust foo
  mail: [email protected]
  Account Lock: FALSE
  Last Password Change: 20170721085748Z
----------------------------------------
  Name: cust xyz
  mail: [email protected]
  Account Lock: TRUE
  Last Password Change: 20181210131249Z
----------------------------------------
  Name: cust bar
  mail: [email protected]
  Account Lock: FALSE
  Last Password Change: 20170412190854Z
----------------------------------------
  Name: cust abc
  mail: [email protected]
  Account Lock: FALSE
  Last Password Change: 20191030080405Z
----------------------------------------

I want to change Last Password Change data format to YYYY-MM-DD but not sure how to do that with sed or awk or is there any other method, I can try for loop it and use date -d option but not sure if there is easier way to do with regex

Answer 1

Since all you're doing is adding two dashes, and dropping some extra characters, there's not much need for date.

$ sed -Ee 's/(Last Password Change: )(....)(..)(..).*Z/\1\2-\3-\4/' < foo.txt
...
  Name: cust foo
  mail: [email protected]
  Account Lock: FALSE
  Last Password Change: 2017-07-21
...

For a stricter pattern, the dots (that match any character) could be replaced with [0-9] to only match digits. \1 etc. in the replacement of course expand to what ever the patterns in parenthesis matched.

Answer 2

This is my proposal:

sed -E 's/([0-9]{4})([0-9]{2})([0-9]{2})[0-9]{6}Z/\1-\2-\3/' file

Output:

  Name: cust foo
  mail: [email protected]
  Account Lock: FALSE
  Last Password Change: 2017-07-21
----------------------------------------
  Name: cust xyz
  mail: [email protected]
  Account Lock: TRUE
  Last Password Change: 2018-12-10
----------------------------------------
  Name: cust bar
  mail: [email protected]
  Account Lock: FALSE
  Last Password Change: 2017-04-12
----------------------------------------
  Name: cust abc
  mail: [email protected]
  Account Lock: FALSE
  Last Password Change: 2019-10-30
----------------------------------------

Answer 3

I was able to accomplish this with the following awk command:

awk -F\: '$1 ~ /Last Password Change/{ OFS=":"; $2 = substr($2, 1, 5)"-"substr($2, 6, 2)"-"substr($2, 8, 2) }1'

Using : as a field separator, if the first column matches Last Password Change we will then use substr to extract the year, month, and date and replace the second column with those values in the format you desire.