a shell environment variable
Matches a shell environment variable. It finds the match anywhere inside the text. There is 1 capture group.
Pattern
/\$\{?([A-Z_][A-Z0-9_]*)\}?/- Match scope
- anywhere inside the text
- Capture groups
- 1
- What it catches in the first example
- $HOME
Try it yourself
Type any text and the parts this expression catches are highlighted. It runs in your browser and is never sent anywhere.
$HOME
${DATABASE_URL}
echo $PATH
3 matches
Examples that match
- $HOME
- ${DATABASE_URL}
- echo $PATH
Examples that do not match
- $lower
- PATH
- ${1}
Other expressions in this group
from ['\"]([^'\"]+)['\"]the path in an import statement#[0-9a-fA-F]{6}\ba hex colour inside running textTODO:?\s*(.*)a TODO note left in a comment\d+(px|em|rem|%)a number with a CSS unit!\[([^\]]*)\]\(([^)]+)\)a Markdown image^[-*+]\s+(.+)$a Markdown list item--[^\n]*a SQL line comment[A-Za-z0-9_-]{11}a YouTube video idHow to read this
- With ^ and $ around it, the whole string must match; without them the match can sit anywhere. Always anchor an expression you use for validation.
- Round brackets ( ) capture what they wrap. When you only need grouping, write (?: ) so the numbering of later groups does not shift.
- Every expression here is checked against its examples. Even so, "looks like an email" and "is a real inbox" remain different questions.
- Nested open-ended repeats such as (a+)+ can blow up on certain inputs. Look for that shape before pasting someone else’s expression into your code.
Frequently asked questions
Q. What is the regex for a shell environment variable?
\$\{?([A-Z_][A-Z0-9_]*)\}?.
Q. Which strings match?
Text like $HOME matches; text like $lower does not.
Q. Does the whole string have to match?
No. It finds the part anywhere inside the text. Add ^ and $ around it if you want a whole-string check.
Q. How do I use what it caught?
There is one capture group, so you can read them from match[1] onwards.