Passing command arguments using heredoc syntax

This post is over three years old. Some of it may no longer reflect current tooling or my current view.

This trick works for both Bash and zsh.

I wanted to pass the following as an argument to the sqlite-utils CLI tool:

insert into documents select
  substr(s3_ocr_etag, 2, 8) as id,
  key as title,
  key as path,
  replace(s3_ocr_etag, '"', '') as etag
from
  index2.ocr_jobs;

Problem: this contains both single AND double quotes, which makes string escaping a tiny bit tricky.

Solution: use heredoc syntax:

sqlite-utils sfms.db --attach index2 index.db "$(cat <<EOF
insert into documents select
  substr(s3_ocr_etag, 2, 8) as id,
  key as title,
  key as path,
  replace(s3_ocr_etag, '"', '') as etag
from
  index2.ocr_jobs;
EOF
)"

Breaking that apart: the main trick here is to use cat <<EOF ... EOF to wrap the literal chunk of text:

$(cat <<EOF
insert into documents select
  substr(s3_ocr_etag, 2, 8) as id,
  key as title,
  key as path,
  replace(s3_ocr_etag, '"', '') as etag
from
  index2.ocr_jobs;
EOF
)

Then to pass it as an argument to the sqlite-utils command use "$(cat ...)" - the double quotes around that ensure that tokens in that input are not treated as separate arguments by zsh/bash.

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