You can specify singularly formatted extractions within props.conf directly, or if you need multiple formats you can use a combination of props and transforms. There are default extractions built into Splunk for apache access and error logs. These can be referenced in $SPLUNK_HOME/etc/system/default/transforms.conf under the "access-extractions" stanza:
[access-extractions]
# matches access-common or access-combined apache logging formats
# Extracts: clientip, clientport, ident, user, req_time, method, uri, root, file, uri_domain, uri_query, version, status, bytes, referer_url, referer_domain, referer_proto, useragent, cookie, other (remaining chars)
# Note: referer is misspelled in purpose because that is the "official" spelling for "HTTP referer"
REGEX = ^[[nspaces:clientip]]\s++[[nspaces:ident]]\s++[[nspaces:user]]\s++[[sbstring:req_time]]\s++[[access-request]]\s++[[nspaces:status]]\s++[[nspaces:bytes]](?:\s++"(?<referer>[[bc_domain:referer_]]?+[^"]*+)"(?:\s++[[qstring:useragent]](?:\s++[[qstring:cookie]])?+)?+)?[[all:other]]
If you need to make a custom format, you could use the above as a template for a new extraction for your particular custom log file.
