how to format string to date in shell correctly

Question

I am generating string using date +"%Y%m%d%H" and reading the same string to convert back as date. somehow reverse is not working. and %Y is treated as first six characters

# date +"%Y%m%d%H"
2017030216

# date -d 2017030215 +%Y
201703

# date -d 2017030215 +%m
02

Why doesn't this return 2017?

John Zwinck · Accepted Answer · 2017-03-03 00:18:50Z

2

You are passing invalid strings to -d, i.e. strings which are not in accordance with its expected format. The documentation of that format is here: https://www.gnu.org/software/coreutils/manual/html_node/Date-input-formats.html

"2017030215" is not a valid date/time string in most systems, and date -d is no exception. If you want to see how date -d is interpreting your string, just run it without the + option to see the full output. You'll probably be surprised.

answered Mar 3, 2017 at 0:18

John Zwinck

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