How do I delete till non-whitespace in vim?
You may want to try dW. This will move by "WORD" (see help for WORD and word), which looks more appropriate for your question.
The dw won't meet your needs in, for example:
array[1] = 5
Hitting dw while positioned in the a will leave you with:
[1] = 5
But using dW will result in:
= 5
Many of the answers here don't really address the question directly. The asker wants to know how to delete up to the first non-whitespace character. Some of the answers will technically work, but let's take a look at how to do this explicitly.
The following examples demonstrate how to do this in normal mode with variations that account for the starting position of the cursor. The u̲nderlined c̲haracters indicate the cursor position:
dw: foo_ bar → foob̲ar
The delete word command, described in other answers, works just fine to delete up to the next non-whitespace character when our cursor is positioned before the target.
db: foo b̲ar → b̲ar
Naturally, we'd want to try the inverse of dw to delete backwards to the first non-whitespace character before the cursor. However, as shown above, the delete back-word command deletes more than we expect—it erases the previous word as well. For this case, we should use:
dT<?>: foo b̲ar → foob̲ar
...where <?> is the first non-whitespace character before the cursor. The delete back-unTil command erases everything up to but not including the character <?>, which, in this case, is the character o at the end of "foo".
dt<?>: foo_ bar → foob̲ar
Similar to the previous command, we can use delete until (with a lowercase "t") to delete characters forward until the next <?> character (the b in "bar", for this example). This achieves the same result as dw for the purpose of this question.
diw: foo _ bar → foob̲ar
If our cursor is positioned in the middle of the whitespace, we can use the delete inner word command to remove the whitespace from both sides.
d/<?>↵:
foo_ \n bar
→
foob̲ar
If the whitespace we want to remove includes line-breaks, we can use the command shown above to delete until matched pattern of <?>, where the pattern in this case is just the first non-whitespace character. As shown, press Enter to complete this command.
When the first non-whitespace character occurs at the beginning of the line after the break, Vim will remove the whitespace, but leave the target on the next line. We need to add J to the above command to Join the lines (an uppercase "j").
d/<?>↵J:
foo_ \nbar
→
foob̲ar
The sequence dw will delete all characters from the cursor until the next word. This means that if you execute the command while standing in the middle of a word, it will delete the remainder of that word and subsequent whitespaces. May or may not be what you're looking for.