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= Multiline comments in POSIX sh
:categories: sh
:posixsh: https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html#tag_19_07_04
I realized one can use heredocs for multiline comments in sh:
[source,sh]
----
cat <<'COMMENT' > /dev/null
if wip; then
unfinished and broken syntax >
fii
COMMENT
----
...instead of:
[source,sh]
----
# if wip; then
# unfinished and broken syntax >
# fii
----
What is going on: the {posixsh}[language defines] `<<` as a redirect of the
"here-document" type. After `<<` you can put anything, and sh will use that as
a token to look for on the following lines:
[source,sh]
----
cat <<'bleh'
...
bleh
----
Make sure to include the `'quotes'` around the word, otherwise anything with a
`$` would get replaced just like a `"double-quoted"` string.
"bleh" works fine, like any word would.
But that example left as-is would print the string to stdout. To avoid that, we
shove the contents to `/dev/null`. So it isn't technically a comment, its more
like a constant string that gets emitted and discarded.
Sure its hacky, but at this point what in sh isn't? It even supports nesting!
[source,sh]
----
cat <<'COMMENT1' > /dev/null
cat <<'COMMENT' > /dev/null
# ... code ...
COMMENT
COMMENT1
----
I've never committed any code with this, just used while debugging sh code.
Make sure to handle with care
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