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Tags: command-line   bash   redirect  
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Title: In what order does the shell execute commands and stream redirection?
ID: /2016/12/17/In-what-order-does-the-shell-execute-commands-and-stream-redirection_
Created: December 17, 2016
Upload: November 24, 2022    Layout:  post
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It’s always left to right… except when

Just like in Math we do left to right except multiplication and division is done before addition and subtraction, except operations inside parenthesis (+ -) would be done before multiplication and division.

As per the Bash beginners guide here (Bash Beginners Guide) there are 8 orders of hierarchy of what comes first (before left to right):

  1. Brace expansion β€œ{}”
  2. Tilde expansion β€œ~”
  3. Shell parameter and variable expression β€œ$”
  4. Command substitution β€œ$(command)”
  5. Arithmetic expression β€œ$((EXPRESSION))”
  6. Process Substitution what we are talking about here β€œ<(LIST)” or β€œ>(LIST)”
  7. Word Splitting β€œβ€™< space>< tab>< newline>’”
  8. File Name Expansion β€œ*”, β€œ?”, etc.

So it’s always left to right… except when…

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