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Is there a reason to use + or - in date arguments?

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-2

I use date +%F-%T to show date and time in this format: 2019-08-15-21:34:58.

From man date:

%F full date; same as %Y-%m-%d

%T time; same as %H:%M:%S

I recognized no explanation for + or -.

I later understood that the backslashes are escaping, the plus is arguments prefix and the hyphen is just a string-like separation (date-time),

and also, that some use the simpler +'%F-%T' or +"%F-%T" instead.

Is there a reason to use + or - in date arguments?

shell-script cron syntax

share|improve this question

edited yesterday

JohnDoea

asked yesterday

JohnDoeaJohnDoea

911 gold badge1111 silver badges4646 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What happens if you run the command without the backslashes? It produces the same output on my system (date 8.31).
  
  – Sparhawk
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I remembered I tried it once and recall it worked the same. I understand it should work the same.
  
  – JohnDoea
  yesterday
  

  
  
  
  

add a comment | 

-2

I use date +%F-%T to show date and time in this format: 2019-08-15-21:34:58.

From man date:

%F full date; same as %Y-%m-%d

%T time; same as %H:%M:%S

I recognized no explanation for + or -.

I later understood that the backslashes are escaping, the plus is arguments prefix and the hyphen is just a string-like separation (date-time),

and also, that some use the simpler +'%F-%T' or +"%F-%T" instead.

Is there a reason to use + or - in date arguments?

shell-script cron syntax

share|improve this question

edited yesterday

JohnDoea

asked yesterday

JohnDoeaJohnDoea

911 gold badge1111 silver badges4646 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What happens if you run the command without the backslashes? It produces the same output on my system (date 8.31).
  
  – Sparhawk
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I remembered I tried it once and recall it worked the same. I understand it should work the same.
  
  – JohnDoea
  yesterday
  

  
  
  
  

add a comment | 

I use date +%F-%T to show date and time in this format: 2019-08-15-21:34:58.

From man date:

%F full date; same as %Y-%m-%d

%T time; same as %H:%M:%S

I recognized no explanation for + or -.

I later understood that the backslashes are escaping, the plus is arguments prefix and the hyphen is just a string-like separation (date-time),

and also, that some use the simpler +'%F-%T' or +"%F-%T" instead.

Is there a reason to use + or - in date arguments?

shell-script cron syntax

share|improve this question

edited yesterday

JohnDoea

asked yesterday

JohnDoeaJohnDoea

911 gold badge1111 silver badges4646 bronze badges

share|improve this question

edited yesterday

JohnDoea

asked yesterday

JohnDoeaJohnDoea

911 gold badge1111 silver badges4646 bronze badges

share|improve this question

edited yesterday

JohnDoea

asked yesterday

JohnDoeaJohnDoea

911 gold badge1111 silver badges4646 bronze badges

asked yesterday

JohnDoeaJohnDoea

911 gold badge1111 silver badges4646 bronze badges

asked yesterday

JohnDoeaJohnDoea

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1 Answer
1

active

oldest

votes

6

The backslashes do nothing.

The - and + characters do not need to be escaped, because they are not special in any way in the syntax of any shell.

$ set -o xtrace

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:46

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:50

As you can see in the above trace output, the command that gets executed by the shell is the same regardless of the backslashes. Note too that the trace output is only "debugging output" from the shell and that whatever commands it outputs generally are not suitable for shell input.

The + introduces a date format specification. And the - is just a literal dash, part of the format specification (will be a dash in the output too).

The command date +%F-%T is the same as date +%F-%T. You will often also see the date format quoted, as in date +'%F-%T'. This makes no difference here as the format is a single word, but in date +'%F %T' it needs to be quoted to keep the shell from splitting the format on the space into two separate arguments to date.

What does makes a difference is the % characters. You would want to escape these if you use them in a crontab specification. See e.g. How can I execute `date` inside of a cron tab job?

The % character was special in the syntax of the fish shell prior to version 3.0 (for job expansions) but only when the first character of a word (so not here when after a +). Similarly, in zsh, a leading % character is special in that a ? following it is not taken as a glob operator (to allow things like kill %?cmd without having to quote the ?), but again that doesn't apply here.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda♦Kusalananda

160k1818 gold badges316316 silver badges502502 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  For some reason though, Busybox's shell escapes the plus-sign when tab-completing.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkkachu Not for me in that shell. What are you completing?
  
  – Kusalananda♦
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  just filenames. Actually it seems to escape about everything that's not a-z0-9_-, so it's probably just being careful, dunno.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Note that in the rc or akanga shells, backslash is not special, so date +%T would be different from date +%T there (the latter being treated the same as date '+%T' and so causing a syntax error by date)
  
  – Stéphane Chazelas
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Note that some shells' xtrace do not output code which when reinput would produce the same outcome, and some could preserve the quoting from the input. So you may want to clarify that your test output there is run from bash or any other shell that behaves in a similar way.
  
  – Stéphane Chazelas
  yesterday
  

  
  
  
  

 | 
show 1 more comment

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6

The backslashes do nothing.

The - and + characters do not need to be escaped, because they are not special in any way in the syntax of any shell.

$ set -o xtrace

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:46

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:50

As you can see in the above trace output, the command that gets executed by the shell is the same regardless of the backslashes. Note too that the trace output is only "debugging output" from the shell and that whatever commands it outputs generally are not suitable for shell input.

The + introduces a date format specification. And the - is just a literal dash, part of the format specification (will be a dash in the output too).

The command date +%F-%T is the same as date +%F-%T. You will often also see the date format quoted, as in date +'%F-%T'. This makes no difference here as the format is a single word, but in date +'%F %T' it needs to be quoted to keep the shell from splitting the format on the space into two separate arguments to date.

What does makes a difference is the % characters. You would want to escape these if you use them in a crontab specification. See e.g. How can I execute `date` inside of a cron tab job?

The % character was special in the syntax of the fish shell prior to version 3.0 (for job expansions) but only when the first character of a word (so not here when after a +). Similarly, in zsh, a leading % character is special in that a ? following it is not taken as a glob operator (to allow things like kill %?cmd without having to quote the ?), but again that doesn't apply here.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda♦Kusalananda

160k1818 gold badges316316 silver badges502502 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  For some reason though, Busybox's shell escapes the plus-sign when tab-completing.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkkachu Not for me in that shell. What are you completing?
  
  – Kusalananda♦
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  just filenames. Actually it seems to escape about everything that's not a-z0-9_-, so it's probably just being careful, dunno.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Note that in the rc or akanga shells, backslash is not special, so date +%T would be different from date +%T there (the latter being treated the same as date '+%T' and so causing a syntax error by date)
  
  – Stéphane Chazelas
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Note that some shells' xtrace do not output code which when reinput would produce the same outcome, and some could preserve the quoting from the input. So you may want to clarify that your test output there is run from bash or any other shell that behaves in a similar way.
  
  – Stéphane Chazelas
  yesterday
  

  
  
  
  

 | 
show 1 more comment

6

The backslashes do nothing.

The - and + characters do not need to be escaped, because they are not special in any way in the syntax of any shell.

$ set -o xtrace

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:46

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:50

As you can see in the above trace output, the command that gets executed by the shell is the same regardless of the backslashes. Note too that the trace output is only "debugging output" from the shell and that whatever commands it outputs generally are not suitable for shell input.

The + introduces a date format specification. And the - is just a literal dash, part of the format specification (will be a dash in the output too).

The command date +%F-%T is the same as date +%F-%T. You will often also see the date format quoted, as in date +'%F-%T'. This makes no difference here as the format is a single word, but in date +'%F %T' it needs to be quoted to keep the shell from splitting the format on the space into two separate arguments to date.

What does makes a difference is the % characters. You would want to escape these if you use them in a crontab specification. See e.g. How can I execute `date` inside of a cron tab job?

The % character was special in the syntax of the fish shell prior to version 3.0 (for job expansions) but only when the first character of a word (so not here when after a +). Similarly, in zsh, a leading % character is special in that a ? following it is not taken as a glob operator (to allow things like kill %?cmd without having to quote the ?), but again that doesn't apply here.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda♦Kusalananda

160k1818 gold badges316316 silver badges502502 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  For some reason though, Busybox's shell escapes the plus-sign when tab-completing.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkkachu Not for me in that shell. What are you completing?
  
  – Kusalananda♦
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  just filenames. Actually it seems to escape about everything that's not a-z0-9_-, so it's probably just being careful, dunno.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Note that in the rc or akanga shells, backslash is not special, so date +%T would be different from date +%T there (the latter being treated the same as date '+%T' and so causing a syntax error by date)
  
  – Stéphane Chazelas
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Note that some shells' xtrace do not output code which when reinput would produce the same outcome, and some could preserve the quoting from the input. So you may want to clarify that your test output there is run from bash or any other shell that behaves in a similar way.
  
  – Stéphane Chazelas
  yesterday
  

  
  
  
  

 | 
show 1 more comment

The backslashes do nothing.

The - and + characters do not need to be escaped, because they are not special in any way in the syntax of any shell.

$ set -o xtrace

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:46

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:50

As you can see in the above trace output, the command that gets executed by the shell is the same regardless of the backslashes. Note too that the trace output is only "debugging output" from the shell and that whatever commands it outputs generally are not suitable for shell input.

The + introduces a date format specification. And the - is just a literal dash, part of the format specification (will be a dash in the output too).

The command date +%F-%T is the same as date +%F-%T. You will often also see the date format quoted, as in date +'%F-%T'. This makes no difference here as the format is a single word, but in date +'%F %T' it needs to be quoted to keep the shell from splitting the format on the space into two separate arguments to date.

What does makes a difference is the % characters. You would want to escape these if you use them in a crontab specification. See e.g. How can I execute `date` inside of a cron tab job?

The % character was special in the syntax of the fish shell prior to version 3.0 (for job expansions) but only when the first character of a word (so not here when after a +). Similarly, in zsh, a leading % character is special in that a ? following it is not taken as a glob operator (to allow things like kill %?cmd without having to quote the ?), but again that doesn't apply here.

share|improve this answer

edited yesterday

answered yesterday

Kusalananda♦Kusalananda

160k1818 gold badges316316 silver badges502502 bronze badges

$ set -o xtrace

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:46

$ date +%F-%T

+ date +%F-%T

2019-08-15-11:51:50

share|improve this answer

edited yesterday

answered yesterday

Kusalananda♦Kusalananda

160k1818 gold badges316316 silver badges502502 bronze badges

answered yesterday

Kusalananda♦Kusalananda

160k1818 gold badges316316 silver badges502502 bronze badges

answered yesterday

Kusalananda♦Kusalananda

160k1818 gold badges316316 silver badges502502 bronze badges