Regex or shell command
Coding
Give examples of what should and should not match, and get one pattern with a line of explanation.
Fill the blanks and it copies as you filled it
Build me one regular expression.
- What I'm trying to do:
- Real input samples: [paste two or three]
- Should match:
- Should not match:
- One pattern and one line of explanation0 of 3 blanks filled · anything left blank copies with its brackets
What this prompt does
Compared with asking the same thing without the length and format lines.estimate
Estimated output tokens
1,400
Asked loosely
180
This prompt
Energy (Wh)
1.215
Asked loosely
0.423
This prompt
Token counts are estimated from character counts, not measured. Energy uses the per-band figures measured by Jegham et al. 2025 as published.
What that saves
15.8 Wh · 5.54 gCO₂e · 74 mL — assuming 20 uses a day
Tap a card for how the conversion was done.
Reported backfire — Specifying output lengthSpecifying a length longer than needed backfires (a 34% increase in 11% of scenarios)
Where these figures come from
We read the prompt to see whether it carries that instruction. The percentages below are published figures for the rule itself, not a measurement of what this prompt saves.
Specifying output length
38.7%mean reduction · 95% CI 29.7–47.7%
Podder et al. 2026 BP#5 · 18 use cases / 57 prompts
by modelGPT-4o 35%Command R+ 49%Mistral-7B 32%
Reduced in every scenario. No backfire reported