CODEWITHSUNDEEP
bashprocess-substitution
Pushparaj
Pushparaj

Reputation: 1059

How does "var=>(...) somecommand" work?

  #1   
   f() {
        cat "$1" >"$x"
    }
  #2   
    x=>(tr '[:lower:]' '[:upper:]') f <(echo 'hi there')

In #2 which part is executed first? x=>(tr '[:lower:]' '[:upper:]') or f <(echo 'hi there') . Is #2 is a compound compound or a single command?

Upvotes: 0

Views: 40

Answers (1)

Charles Duffy
Charles Duffy

Reputation: 295403

A single command can have any number of var=value prefixes; these variables are exported to the environment for the duration of that single command, and do not exist later. This isn't bash-specific, but is part of the POSIX sh standard.

"Which part is executed first?" isn't a meaningful question. The process substitution whose FIFO's filename (being a /dev/fd entry and an anonymous FIFO if the OS permits same) is stored in X is started first, but execution is asynchronous. (That said, because the output of the process substitution writing hi there is redirected as input for the one running tr, the one with the echo necessarily blocks until tr is ready to read what it's writing).

Upvotes: 3

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