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I am trying to save a file with today's date as part of name.
To save file, we can just do :w myFile. To get today's date, we can use strftime. Ex: :echo strftime("%F") " returns 2020-03-27.
Now I would like to combine both - to save with today's date. Something like:
:w 'myFile-(strftime("%F")'
Is it possible to save file with today's date (myFile-2020-03-27.) in Vim?
There are two ways to do this.
The first one is interactive, using CTRL-R = in the Ex command-line to enter an expression and evaluate it.
Start by typing the command as usual: :w myFile-, then press CTRL-R, =. You'll now have a = prompt where you can enter an expression. Enter strftime("%F") and press "Enter", Vim will evaluate that to 2020-03-27 (assuming that's today's date) and will now display the command-line as :w myFile-2020-03-27, which you can then execute or further edit as you like.
Another option is to use the :execute command to execute a string as an Ex command. In which case you can simply use:
:exe 'w myFile-'.strftime("%F")
Note that . is the string concatenation operator here. This latter form with :execute is particularly useful in Vim scripts or functions.
If you frequently find yourself wanting to insert the current date into command-line commands you could set up a mapping like this using something similar to what's in the existing answer:
:cnoremap YMD <C-R>=strftime("%Y-%m-%d")<CR>
Your use case then would be to enter
:w myFile-YMD
Which, right after you hit D, will be converted to
:w myFile-2020-03-27
and then you just hit Enter to submit it. I have this in my vimrc and it comes in handy.
:cabbrev <expr> YMD strftime("%F") is a better way to implement it. Using a cabbrev means it won't make it awkward to type a single Y or YM on the command line. It will still properly expand if YMD appears after a -. Also using <expr> is much simpler than <C-R>= here, since it's possible to do so. One small downside of cabbrev is that it doesn't expand on D, so if you type :w myFile-YMD<CR> you won't "see" the date until the command is completed. You can work around that by expanding it explicitly with <C-]> though.
cnoremap? Putting aside the fact that "Y" or "YM" (and, for many people I'd wager, capital letters in general) are used relatively infrequently on the command line there's no delay if I type something other than "MD"/"D" after them. Vim only waits if you wait. And then it only waits for however long you've configured. I have 'ttimeout' enabled and 'ttimeoutlen' set to 100 (these are also Vim's recommended values as you can see in defaults.vim). There's also no problem using "YMD" after a -. (cont)
<C-]> if I don't have to.