bash.expansion.rme

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..                                                                            ..
..                     Bash Expansions and Substitutions                      ..
..                                                                            ..
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# ------------------------------- INTRODUCTION ------------------------------- #

   Before executing each command, Bash checks the statement for any syntax
   elements which should be interpreted rather than taken literally. To start,
   Bash splits the statement into tokens (words) and scans them for any special
   characters or reserved words; if any are encountered, the elements are 
   expanded or substituted to new text (and possibly new tokens).

   After all of the expansions/substitutions are done, all quotes that are not
   meant literally (i.e. the quotes that mark contiguous words) are removed
   from the command line text in a process called quote-removal.


                        -> *> #>    OVERVIEW    <# <* <-                        

   Here are the possible expansions/substitutions in order of execution:

      ~> Brace Expansion
         ~> {X,Y,Z}
         ~> {X..Y}
         ~> {X..Y..Z}

      ~> Tilde Expansion
         ~> ~ ; ~+ ; ~-

      The following four expansions/substitutions have the same precedence,
      and so are processed in a left-to-right fashion.
      |---
      |  ~> Parameter Expansion
      |     ~> $WORD
      |     ~> ${WORD:-char} ; ${WORD%%ext} ; ${WORD/pattern/string}
      |
      |  ~> Arithmetic Expansion
      |     ~> $(( EXPRESSION ))
      |     ~> $[ EXPRESSION ]
      |
      |  ~> Command Substitution
      |     ~> $( COMMAND )
      |     ~> ` COMMAND `
      |
      |  ~> Process Substitution
      |     ~> <( COMMAND )
      |     ~> >( COMMAND )
      |---

      ~> Word Splitting
         ~> IFS=$' \t\n'  # <space>, <tab>, <newline>

      ~> Pathname Expansion (a.k.a. globbing)
         ~> *.txt
         ~> page_1?.html


=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=
|                                  ~ finis ~                                   |
=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=~+~=