coproc: add page (#9636)

* coproc: add page

* Fix formatting errors

* Fix formatting errors

* Update pages/common/coproc.md

* Update pages/common/coproc.md

* Update pages/common/coproc.md

* Update pages/common/coproc.md

* Update pages/common/coproc.md

* Update pages/common/coproc.md

* Fix phrasing and formatting

* Change capitalisation

pages/common/coproc.md

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+# coproc
+
+> Bash builtin for creating interactive asynchronous subshells.
+> More information: <https://www.gnu.org/software/bash/manual/bash.html#Coprocesses>.
+
+- Run a subshell asynchronously:
+
+`coproc { {{command1; command2; ...}}; }`
+
+- Create a coprocess with a specific name:
+
+`coproc {{name}} { {{command1; command2; ...}}; }`
+
+- Write to a specific coprocess `stdin`:
+
+`echo "{{input}}" >&"${{{name}}[1]}"`
+
+- Read from a specific coprocess `stdout`:
+
+`read {{variable}} <&"${{{name}}[0]}"`
+
+- Create a coprocess which repeatedly reads `stdin` and runs some commands on the input:
+
+`coproc {{name}} {  while read line; do {{command1; command2; ...}}; done }`
+
+- Create and use a coprocess running `bc`:
+
+`coproc BC { bc --mathlib; }; echo "1/3" >&"${BC[1]}"; read output <&"${BC[0]}"; echo "$output"`

pages/linux/coproc.md

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+# coproc
+
+> Bash builtin for creating interactive asynchronous subshells.
+> More information: <https://www.gnu.org/software/bash/manual/bash.html#Coprocesses>.
+
+- Run a subshell asynchronously:
+
+`coproc { {{command1; command2; ...}}; }`
+
+- Create a coprocess with a specific name:
+
+`coproc {{name}} { {{command1; command2; ...}}; }`
+
+- Write to a specific coprocess `stdin`:
+
+`echo "{{input}}" >&"${{{name}}[1]}"`
+
+- Read from a specific coprocess `stdout`:
+
+`read {{variable}} <&"${{{name}}[0]}"`
+
+- Create a coprocess which repeatedly reads `stdin` and runs some commands on the input:
+
+`coproc {{name}} {  while read line; do {{command1; command2; ...}}; done }`
+
+- Create a coprocess which repeatedly reads `stdin`, runs a pipeline on the input, and writes the output to `stdout`:
+
+`coproc {{name}} { while read line; do echo "$line" | {{command1 | command2 | ...}} | cat /dev/fd/0; done }`
+
+- Create and use a coprocess running `bc`:
+
+`coproc BC { bc --mathlib; }; echo "1/3" >&"${BC[1]}"; read output <&"${BC[0]}"; echo "$output"`