Only read stdin when no files are given, or when a flag asks for it #736

Today

RexReplace reads stdin every time stdin is not a terminal, also when files are given. It waits for stdin to close before it starts.

Some environments (CI runners, agent harnesses, cron, docker exec) give the process a pipe that is open, but never written to and never closed. Then RexReplace hangs:

> sleep 3 | grep foo a.txt                 # done at once
> sleep 3 | rexreplace foo bar a.txt -o    # waits 3 seconds

grep, sed, awk and jq do not hang, as they only read stdin when no file is given.

Change

Only read stdin when it is asked for:

In all other cases stdin is not touched, so the run starts at once.

• Add --pipe (-p): read the piped data and make it available to the JavaScript of --replacement-js as pipe. The warning that piped data is not used stays.
• Add --js-pipe as a shorthand for --replacement-js --pipe (-jp).
• Remove -P, --void-pipe and RR_VOID_PIPE.
• Remove the note about the hang from the README.

> rexreplace foo bar '*.md'                          # stdin is not read
> cat names.txt | rexreplace foo bar '*.md' -R       # replacement from stdin
> cat list.txt | rexreplace x 'pipe' '*.md' --js-pipe # code gets the piped data

Good to know

• -P and RR_VOID_PIPE were never released (npm has v7.1.14), so removing them breaks nothing.
• No timeout: a slow writer and a writer that never writes look the same until the pipe closes.