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up vote 6 down vote favorite
1

I want to make the date command with nice formatting like this:

$ date +"%Y-%m-%d %H:%M:%S"
2015-09-17 16:51:58

But I want to save this in variable, so I could call from script like this: echo "$(nice_date) [WARNING] etc etc"

However it does not work

$ nice_date="date +%Y-%m-%d %H:%M:%S"
$ echo "$($nice_date)"
date: extra operand ‘%H:%M:%S’
Try 'date --help' for more information.

$ nice_date="date +\"%Y-%m-%d %H:%M:%S\""
$ echo "$($nice_date)"
date: extra operand ‘%H:%M:%S"’
Try 'date --help' for more information.

$ nice_date='date +"%Y-%m-%d %H:%M:%S"'
$ echo "$($nice_date)"
date: extra operand ‘%H:%M:%S"’
Try 'date --help' for more information.

What is correct way to do this, so that date command to get one correct argument?

share|improve this question

migrated from serverfault.com Sep 18 '15 at 4:43

This question came from our site for system and network administrators.
    
As a side note, your date format string can be shortened to "%F %T" if you are using GNU date. – jordanm Sep 17 '15 at 14:14
    
The problem's the space. If you use nice_date="date +%Y-%m-%d-%H:%M:%S", it works. I can't currently see how to get that space protected from the second shell. – MadHatter Sep 17 '15 at 14:20
up vote 10 down vote accepted

The reason your example fails is because of the way the shell's word splitting works. When you run "$($nice_date)", the shell is executing the date command with two arguments, "+%Y-%m-%d" and "%H:%M:%S". This fails because the format string for date must be a single argument.

The best way to do this is to use a function instead of storing the command in a variable:

format_date() {
  # echo is not needed
  date "+%Y-%m-%d %H:%M:%S" "$1"
}
format_date
format_date "2015-09-17 16:51:58"
echo "$(format_date) [WARNING] etc etc"

If you really wanted to store the command in a variable, you can use an array:

nice_date=(date "+%Y-%m-%d %H:%M:%S")
# again echo not needed
"${nice_date[@]}" "2015-09-17 16:51:58"

For more details on the complex cases of storing a command in a variable, see BashFAQ 050.

share|improve this answer
    
Thank you, but I am curious why my approach is not working, can you elaborate on that? – gilbertasm Sep 17 '15 at 14:14
    
@gilbertasm answer updated – jordanm Sep 17 '15 at 14:20
    
I'm getting date: extra operand ‘’ errors with both approaches above – Jeff Puckett II Apr 24 at 22:34
up vote 0 down vote

Please try out the below:

You need to add the symbol "`" the symbol that is on the tilde key in the keyboard. The symbol says the shell to execute the command first and then assign to the variable.

[root@RHEL01 ~]# My_Var=`date +"%Y-%m-%d %H:%M:%S"`
[root@RHEL01 ~]# echo $My_Var
2015-09-17 10:05:30
[root@RHEL01 ~]#
share|improve this answer
    
Same problem as Iain's answer. – MadHatter Sep 17 '15 at 14:09
up vote 0 down vote

I agree a function is the best way to go. As an alternative simply store the format as a variable rather than the whole command:

$ nice_date='+%Y-%m-%d %H:%M:%S'
$ echo $(date $nice_date)
share|improve this answer
up vote 0 down vote

Instead of:

nice_date="date +%Y-%m-%d %H:%M:%S"
echo "$($nice_date)"

Try:

nice_date_format="+%Y-%m-%d %H:%M:%S"
echo $(date "$nice_date_format")

Also, you don't need the last command substitution:

date "$nice_date_format"
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