How can I extract this substring with a regexp?

I want to extract the number (which could be any nonnegative integer) that comes after "cache", but not the one that comes after "total_cache". I need to be able to do this in a single regular expression, and I can't use lookahead or lookbehind. (I'm doing this in go, which appears to be largely compatible with the tester here: http://regexpal.com/)

cache 5764452352
rss 2929250304
rss_huge 0
mapped_file 283906048
pgpgin 19709097
pgpgout 17586611
pgfault 39612525
pgmajfault 3757
inactive_anon 160579584
active_anon 3931484160
inactive_file 3560427520
active_file 1040818176
unevictable 49152
hierarchical_memory_limit 9223372036854775807
total_cache 5764452352
total_rss 2929250304
total_rss_huge 0
total_mapped_file 283906048
total_pgpgin 19709097
total_pgpgout 17586611
total_pgfault 39612525
total_pgmajfault 3757
total_inactive_anon 160579584
total_active_anon 3931484160
total_inactive_file 3560427520
total_active_file 1040818176
total_unevictable 49152

You need to use FindStringSubmatch and then extract m[1].

http://play.golang.org/p/zOixuvDWsi

This should do it:

^cache\s(\d+)

Working regex example:

http://regex101.com/r/jS6sF6

In the Go programming language, I think you can force multi-line mode by using: (?m)
Like so:

(?m)^cache\s(\d+)

Note: Im not familiar with Go syntax, so please forgive me is this is wrong, but the regex is correct, it just needs to be used with the multi-line flag.

Try this -

^cache[ ](\d+)$

with multi-line(m) flag (In Regex Tester tick the option - ^$ match at line breaks)