Vim regular expression to match string with prefix and suffix

The command below should work unless "any character" means something different for you than for Vim:

:g/abc.*xyz

• . means "any character except an EOL".
• * means "any number (including 0) of the previous atom".
• 1,$ could be shortened to %.
• :global works on the whole buffer by default so you don't even need the %.
• The closing / is not needed if you don't follow :g/pattern by a command as in :g/foo/d.

It seems that inside the collection syntax [..], character classes such as \w can't be used, probably because it tests via character-by-character strategy. From :h /[]:

Matching with a collection can be slow, because each character in the text has to be compared with each character in the collection. Use one of the other atoms above when possible. Example: "\d" is much faster than "[0-9]" and matches the same characters.

You can, however, use similar functionalities specifically prepared for [..] syntax. From :h /[] again :

A character class expression is evaluated to the set of characters belonging to that character class.

examples include:

[:alnum:]     letters and digits                   
[:alpha:]     letters                              
[:blank:]     space and tab characters             
[:cntrl:]     control characters                   
[:digit:]     decimal digits                       
[:graph:]     printable characters excluding space 
[:lower:]     lowercase letters

Once the file gets too large (say, 1GB), ":g/abc.*xyz" becomes quite slow.

I found that

cat fileName | grep abc | grep xyz >> searchResult.txt

is more efficient than using the search function in vim.

I know that this method may return lines that start with "xyz" and end with "abc".

But since this is a rare case in my file(and maybe this doesn't happen quite often for other people), I think I should write this method here.