Documentation
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Overview ¶
Command histprobe drives a shell through a pseudo-terminal with a TWO-ROW prompt and types lines at it one at a time, waiting on a distinct done-marker after each.
It exists because history expansion cannot be measured any other way. It is **interactive by default and off in a script**, so a `-c` probe answers "absent" for a feature that is merely switched off, and the corpus harness runs every case as a command string — a row there would have recorded the same "nothing happened" in all six columns and looked like agreement. The panel table in docs/spec/history.md was produced by this program.
A two-row prompt rather than a one-line PS1, for the reason tworowprobe gives: components can each match the shell they imitate while the composition of them does not.
The marker after every line is what makes the run readable. Raw-mode input is lost silently and a pty read blocks, so the loop waits on text that could only have come from the line before it rather than on a timer, and it never clears the screen between waits. `-rc 'HISTCONTROL=ignorespace'` with a marker that begins with a space keeps the markers out of the history the designators index — without it, `!$` names the marker and the transcript measures the instrument.
histprobe -bin /opt/homebrew/bin/bash -name bash // -rc HISTCONTROL=ignorespace -lines 'echo one two three|echo !!'
Written for #3093.
Source Files