I'd like to define a variable within a process that is piped to a yad progress bar while retaining it outside of that process. e.g:
(a=3 ; sleep 1) | yad --progress --auto-close
echo $a
I'd also like to avoid writing that variable to a temporary file to retrieve later, especially considering it may sometimes be an array, associative array or whatever messy multiline string that would require more code to reconstruct from a file.
I think I should be able to use redirection rather than a pipe but I don't know how exactly in this situation and all my attemps have failed.
Use this, using { } for grouping commands and >( ) for process substitution:
{ a=3; sleep 1; } > >(yad --progress --auto-close)
echo "$a"
you declare the variable in a subshell: ( ), the variable don't exists for the parent shell.
if you use a pipe: |, the command still be in a subshell, that's why the need for > >( ) process substitution.
Process Substitution >(command ...) or <(...) is replaced by a temporary filename. Writing or reading that file causes bytes to get piped to the command inside. Often used in combination with file redirection: cmd1 2> >(cmd2).
See http://mywiki.wooledge.org/ProcessSubstitution
http://mywiki.wooledge.org/BashFAQ/024