# expr - pydoc - phpman

> **TLDR:** Evaluate expressions and manipulate strings.
>
- Get the length of a specific string:
  `expr length "{{string}}"`
- Get the substring of a string with a specific length:
  `expr substr "{{string}}" {{from}} {{length}}`
- Match a specific substring against an anchored pattern:
  `expr match "{{string}}" '{{pattern}}'`
- Get the first char position from a specific set in a string:
  `expr index "{{string}}" "{{chars}}"`
- Calculate a specific mathematic expression:
  `expr {{expression1}} {{+|-|*|/|%}} {{expression2}}`
- Get the first expression if its value is non-zero and not null otherwise get the second one:
  `expr {{expression1}} \| {{expression2}}`
- Get the first expression if both expressions are non-zero and not null otherwise get zero:
  `expr {{expression1}} \& {{expression2}}`

*Source: tldr-pages*

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