You can search Slack by custom channel section

Slack provides an in: search modifier to narrow the scope of results to a given channel. Further, multiple in: modifiers will filter results to a set of channels.

The problem I was trying to solve was to search within a large set of channels; too many to bother typing into a single search query.

All the channel names followed a pattern so I was hoping I could use a wildcard filter like in:tech-guild-* but alas no.

However it turns out the in: modifier can act on a custom channel section, and I happened to have a “Tech Guilds” section including all the relevant channels. So in:Tech Guilds was the filter I needed.