{: add page (#15234)

pages/common/{.md

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+# Curly brace
+
+> Multipurpose shell syntax.
+> More information: <https://www.gnu.org/software/bash/manual/bash.html#index-hash>.
+
+- Isolate variable names:
+
+`echo ${HOME}work`
+
+- Brace expand sequences:
+
+`echo {1..3} {a..c}{dir1,dir2,dir3}`
+
+- Check if `variable` is set before returning text:
+
+`echo ${variable:+variable is set and contains $variable}`
+
+- Set default values in case `variable` is unset:
+
+`echo ${variable:-default}`
+
+- Return `variable` length in characters:
+
+`echo ${#variable}`
+
+- Return a string slice:
+
+`echo ${variable:3:7}`
+
+- Recursively expand a `variable`:
+
+`echo ${!variable}`
+
+- Capitalize all the characters:
+
+`echo ${variable^^}`