delete entire line after first whitespace on every line

Question

I have a file (around 1.6 million lines) which formatted like this:

-0.00697468 0 -1.95966e-49 101325 -3.06381  
-0.00697468 0 -1.95966e-49 101325 -3.06381  
-0.00697468 0 -1.95966e-49 101325 -3.06381  
. . .  

After some thousand lines, the format will be changed (no minus sign on the first character), like this:

0.453945 -2.14126e-54 3.40152e-49 101325 214.355  
0.453945 -2.14126e-54 3.40152e-49 101325 214.355  
0.453945 -2.14126e-54 3.40152e-49 101325 214.355  
. . .

So, how to delete the entire line, after the first whitespace on every line? I have tried to search but couldn't get any answer that I want. Thanks! (Note: some lines have different number of character, hence that I cannot simply delete some characters from the end of the line on every line)

Answer 1

The two commands below will reduce every line to the first sequence of non-whitespace character followed by a space:

from
0.453945 -2.14126e-54 3.40152e-49 101325 214.355

to
0.453945 <-- space

But your question is a little confusing so I'm not sure I understood what you want.

With a substitution:

:%s/\(\S\+\s\).*/\1

With a macro:

:%normal! WD

Answer 2

If you wanted to delete entire line starting with a space, This pattern will be useful.

:g/^\s.*/d

• g -global
• ^ - start of the line
• \s - space
• .* - anything after that
• d - delete

If you want the starting whitespace to remain, but delete the remaining content, you can use,

:%s/^\(\s\+\).*/\1/g