til/unix/merge-a-sequence-of-lines-of-output.md

Merge A Sequence Of Lines Of Output

More often than not when I'm chaining a sequence of Unix commands together, I'm eventually trying to fan them out or execute each argument separately. I recently had the need for a bunch of separate lines of output to be fanned back in to a single line.

The tool I found for this job is paste (not the most intuitive name).

merge corresponding or subsequent lines of files

I was listing out all the categories that my active TIL posts full under. I used the following command to do that.

❯ git ls-files '*/*.md' | cut -d/ -f1 | sort -u
ack
ansible
astro
aws
bash
brew
chrome
...

Those are all my categories, but then the format I really wanted was for them to be all on the same line with a clear delimiter so that I could paste them for use in another script.

The trick is to tack on one more pipe to paste. The -s tells paste to join every line from a given input file (e.g. stdin) onto a single line. The -d allows for overriding the default delimiter (tab) with something like a ,. Lastly, the trailing - tells paste to read from stdin rather than some other named file(s).

❯ git ls-files '*/*.md' | cut -d/ -f1 | sort -u | paste -sd, -
ack,ansible,astro,aws,bash,brew,chrome,claude-code,clojure,css,cursor,deno,devops,docker,drizzle,elixir,gatsby,git,github,github-actions,go,groq,heroku,html,http,inngest,internet,java,javascript,jj,jq,kitty,linux,llm,mac,math,mise,mongodb,mysql,neovim,netlify,next-auth,nextjs,phoenix,planetscale,pnpm,postgres,prisma,python,rails,react,react_native,react-testing-library,reason,remix,rspec,ruby,sed,shell,sqlite,streaming,tailwind,taskfile,tmux,typescript,unix,vercel,vim,vscode,webpack,workflow,xstate,yaml,zed,zod,zsh

See man paste for more details.