indirect expansion, more about arrays

bash_prog_ref.md

@@ -122,11 +122,22 @@ Parameter Expansion
 
 \begin{tabular}{p{2.0cm}p{6cm}}
 \textbf{expansion}           & \textbf{value} \\
-\texttt{\$\{var\}}           & value of \texttt{var} (as a string) \\
+\texttt{\$\{{\itshape var}\}}           & value of \texttt{var} (as a string) \\
 \texttt{\$var}               & short for \texttt{\$\{var\}}, ok iff not prefix of longer word \\
 \texttt{\$\{\#var\}}         & string length of \texttt{\$var} \\
 \end{tabular}
 
+### Indirect Expansion
+
+Variables can hold the names of other variables.
+
+\begin{tabular}{p{2.0cm}p{6cm}}
+\texttt{\$\{!{\itshape name}\}}         & If \texttt{\itshape name} is a \textit{nameref}: expand to the name of the referenced variable.\\
+\texttt{\$\{!{\itshape name}\}}         & If \texttt{\itshape name} is not a
+\textit{nameref}: take \texttt{\${\itshape name}} to be a parameter name, and
+expand it (TVCA).\\
+\end{tabular}
+
 ### Handling null and unset
 
 A parameter is _null_ if its value is the empty string. It is _unset_ if it has _no value_. \
@@ -577,17 +588,35 @@ Creation and Assignment
 Retrieval
 ---------
 
+\texttt{\itshape sub} below ("subscript") stands for either an integer or a string,
+for indexed or associative arrays, respectively.
+
 \begin{tabular}{p{3.0cm}p{5.5cm}}
 \textbf{expression}                          & \textbf{value} \\ 
-\texttt{\${\itshape array}[{\itshape subscript]}}  & the value of array at index
-or key \texttt{{\itshape subscript}}. \\
-\texttt{\${\itshape a}[@]}, \texttt{\${\itshape a}[*]} & \texttt{\${\itshape a}[1] ... \${\itshape a}[n]} \\ 
-\texttt{"\${\itshape a}[*]"}              & \texttt{"\${\itshape a}[1]s\${\itshape a}[2]s...\${\itshape a}[n]"}; separator \texttt{s} is the 1\textsuperscript{st} char of \texttt{\$IFS} (\texttt{space} if unset, empty if null) \\
-\texttt{"\${\itshape a}[@]"}              & \texttt{"\${\itshape a}[1]" "\${\itshape a}[2]" ... "\${\itshape a}[n]"} \\
-\\
+\texttt{\$\{{\itshape array}[{\itshape sub}]\}}  & the value of array \texttt{\itshape array} at index or key \texttt{{\itshape sub}}. \\
+\texttt{\$\{{\itshape a}[@]\}}, \texttt{\$\{{\itshape a}[*]\}} & \texttt{\$\{{\itshape a}[1]\} ... \$\{{\itshape a}[n]\}} \\ 
+\texttt{"\$\{{\itshape a}[*]\}"}              & \texttt{"\$\{{\itshape a}[1]\}s\$\{{\itshape a}[2]\}s...\$\{{\itshape a}[n]\}"}; separator \texttt{s} is the 1\textsuperscript{st} char of \texttt{\$IFS} (\texttt{space} if unset, empty if null) \\
+\texttt{"\$\{{\itshape a}[@]\}"}              & \texttt{"\$\{{\itshape a}[1]\}" "\$\{{\itshape a}[2]\}" ... "\$\{{\itshape a}[n]\}"} \\
+\texttt{"\$\{\#{\itshape array}[{\itshape sub}]\}"}  & length of \texttt{"\$\{{\itshape array}[{\itshape sub}]\}"} \\
+\texttt{\$\{\#{\itshape array}[{\itshape sub}]\}}  & length of \texttt{\$\{{\itshape array}[{\itshape sub}]\}} \\
+\texttt{\$\{\#{\itshape a}[@]\}}, \texttt{\$\{\#{\itshape a}[*]\}} & number of elements in \texttt{\itshape{a}}. \\ %*
+\texttt{\$\{!{\itshape a}[@]\}}, \texttt{\$\{!{\itshape a}[*]\}} & like \texttt{\$\{{\itshape a}[@]\}}, but with the \textit{subscripts} instead of the values \\
+%\texttt{"\$\{!{\itshape a}[*]\}"}              & like \texttt{"\$\{{\itshape a}[*]\}"}, but with the subscripts \\
+%\texttt{"\$\{!{\itshape a}[@]\}"}              & like \texttt{"\$\{{\itshape a}[@]\}"}, but with the subscripts \\
 \end{tabular}
 
 
+Destruction
+-----------
+
+\begin{tabular}{p{3.0cm}p{5.5cm}}
+\textbf{expression}                          & \textbf{value} \\ 
+\texttt{unset {\itshape a}[{\itshape sub}]}  & removes the element at index or key \texttt{{\itshape sub}} from array \texttt{\itshape a}. \\
+\texttt{unset {\itshape a}}  & removes the array \texttt{\itshape a}. \\
+\texttt{unset {\itshape a}[@]}  & removes the array \texttt{\itshape a}. \\
+\texttt{unset {\itshape a}[*]}  & removes the array \texttt{\itshape a}. \\
+\end{tabular} 
+
 
 Functions
 =========
@@ -625,8 +654,7 @@ TODO
 
 * `eval` (and maybe `expr`)
 * `declare`
-* namerefs
-* arrays
+* namerefs (`declare -n`)
 * idioms: read x y < <(...) (use process substitution to set variables)
 * f -o a1 a2 -- you can pass switches and options to functions
 * regexps `[[ $var =~ regexp ]]`