Converting epoch time format saved in a text file to human friendly format

Question

I have a file name simcloud-target.txt where dates are saved in epoch time format i want to convert all the dates to human friendly format and print it as a list (same as the out put shown below so instead of epoch i want it in human friendly hh:mm:00)

sec504@slingshot:~$ cat simcloud-targets.txt
1679450009
1679450014
1679450018
1679450018
1679450022
1679450023
1679450024
1679450024
1679450033
1679450043
1679450046
1679450060
1679450065
1679450071
sec504@slingshot:~$ 

Answer 1

If the Unix timestamps in the file could be prefixed by @, then GNU date could read them in with -f. We may prefix each timestamp with @ using sed like so:

sed 's/^/@/' file

... and we may then use the output of that with GNU date like so:

date -f <(sed 's/^/@/' file)

Given the datestamps in question and my local timezone, this would give us

Wed Mar 22 02:53:29 CET 2023
Wed Mar 22 02:53:34 CET 2023
Wed Mar 22 02:53:38 CET 2023
Wed Mar 22 02:53:38 CET 2023
Wed Mar 22 02:53:42 CET 2023
Wed Mar 22 02:53:43 CET 2023
Wed Mar 22 02:53:44 CET 2023
Wed Mar 22 02:53:44 CET 2023
Wed Mar 22 02:53:53 CET 2023
Wed Mar 22 02:54:03 CET 2023
Wed Mar 22 02:54:06 CET 2023
Wed Mar 22 02:54:20 CET 2023
Wed Mar 22 02:54:25 CET 2023
Wed Mar 22 02:54:31 CET 2023

You may then set the output format you want as you would usually do with date. Here I also show how to use an ordinary pipe instead of a process substitution:

$ sed 's/^/@/' file | date -f - +'%F %T'
2023-03-22 02:53:29
2023-03-22 02:53:34
2023-03-22 02:53:38
2023-03-22 02:53:38
2023-03-22 02:53:42
2023-03-22 02:53:43
2023-03-22 02:53:44
2023-03-22 02:53:44
2023-03-22 02:53:53
2023-03-22 02:54:03
2023-03-22 02:54:06
2023-03-22 02:54:20
2023-03-22 02:54:25
2023-03-22 02:54:31

See the manual for the library function strftime (man 3 strftime) to see what format placeholders you may use.

Answer 2

Since you can use almost anything, you could use (g)awk:

awk '1{$1 = strftime("%F %H:%M:%S", $1); print}' < simcloud-targets.txt

yields (because I'm in a different time zone):

2023-03-22 02:53:29
2023-03-22 02:53:34
2023-03-22 02:53:38
2023-03-22 02:53:38
2023-03-22 02:53:42
…

I offer this, because it will still work even if you have other entries after the timestamp, such as in squid logfiles:

1679468468.282    223 redacted_ip TCP_TUNNEL/200 7160 CONNECT redacted_name:443 - HIER_DIRECT/redacted_ip -

becomes

2023-03-22 08:01:08 223 redacted_ip TCP_TUNNEL/200 7160 CONNECT redacted_name:443 - HIER_DIRECT/redacted_ip -

Answer 3

Like this, with xargs and GNU date:

$ xargs < file -I{} date -d '@{}' "+%F %T"

Or like this, with bourne* bash, dash, ash, yash, ksh, zsh, sh (but not compliant with csh & fish):

$ while read epoch; do date -d "@$epoch" "+%F %T"; done < file

Output

2023-03-22 08:53:29
2023-03-22 08:53:34
2023-03-22 08:53:38
2023-03-22 08:53:38
2023-03-22 08:53:42
2023-03-22 08:53:43
2023-03-22 08:53:44
2023-03-22 08:53:44
2023-03-22 08:53:53
2023-03-22 08:54:03
2023-03-22 08:54:06
2023-03-22 08:54:20
2023-03-22 08:54:25
2023-03-22 08:54:31

---

With perl:

$ perl -nE 'say scalar localtime($_)' file 
Wed Mar 22 08:53:29 2023
Wed Mar 22 08:53:34 2023
Wed Mar 22 08:53:38 2023
Wed Mar 22 08:53:38 2023
Wed Mar 22 08:53:42 2023
Wed Mar 22 08:53:43 2023
Wed Mar 22 08:53:44 2023
Wed Mar 22 08:53:44 2023
Wed Mar 22 08:53:53 2023
Wed Mar 22 08:54:03 2023
Wed Mar 22 08:54:06 2023
Wed Mar 22 08:54:20 2023
Wed Mar 22 08:54:25 2023
Wed Mar 22 08:54:31 2023