bash Cookbook

Formatting Dates for Display

Problem

You need to format dates or time for output.

Solution

Use the date command with a strftime format specification. See “Date and Time String Formatting with strftime” in Appendix A or the strftime manpage for the list of format specifications supported.

# Setting environment variables can be helpful in scripts:
$ STRICT_ISO_8601='%Y-%m-%dT%H:%M:%S%z'   # http://greenwichmeantime.com/info/iso.htm
$ ISO_8601='%Y-%m-%d %H:%M:%S %Z'         # Almost ISO-8601, but more human-readable
$ ISO_8601_1='%Y-%m-%d %T %Z'             # %T is the same as %H:%M:%S
$ DATEFILE='%Y%m%d%H%M%S'                 # Suitable for use in a file name

$ date "+$ISO_8601"
2006-05-08 14:36:51 CDT

gawk "BEGIN {print strftime(\"$ISO_8601\")}"
2006-12-07 04:38:54 EST

# Same as previous $ISO_8601
$ date '+%Y-%m-%d %H:%M:%S %Z'
2006-05-08 14:36:51 CDT

$ date -d '2005-11-06' "+$ISO_8601"
2005-11-06 00:00:00 CST

$ date "+Program starting at: $ISO_8601"
Program starting at: 2006-05-08 14:36:51 CDT

$ printf "%b" "Program starting at: $(date '+$ISO_8601')\n"
Program starting at: $ISO_8601

$ echo "I can rename a file like this: mv file.log file_$(date +$DATEFILE).log"
I can rename a file like this: mv file.log file_20060508143724.log

Discussion

You may be tempted to place the + in the environment variable to simplify the later command. On some systems the date command is more picky about the existence and placement of the + than on others. Our advice is to explicitly add it to the date command itself.

Many more formatting options ...