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shell-expansion.wht (1338B)

      1 Shell Parameter Expansion
      2 ________________________________________________________________________________
      3 
      4 [000] Index
      5 ________________________________________________________________________________
      6 * ........................................................................ [000]
      7 
      8 [000] 
      9 ________________________________________________________________________________
     10 
     11 ${VARxDEFAULT}
     12 
     13 Colon tests for set and not an empty string
     14 No colon tests for only set/unset
     15 
     16 +---------+------------+---------------+----------------+
     17 | Pattern | $VAR unset | $VAR is empty | $VAR not empty |
     18 +---------+------------+---------------+----------------+
     19 |    -    |  default   |             $VAR               |
     20 +---------+------------+---------------+----------------+
     21 |    +    |  nothing   |            default             |
     22 +---------+------------+---------------+----------------+
     23 |   :-    |          default           |      $VAR      |
     24 +---------+------------+---------------+----------------+
     25 |   :+    |          nothing           |     default    |
     26 +---------+------------+---------------+----------------+
     27 |   :=    |       VAR=default          |      $VAR      |
     28 +---------+------------+---------------+----------------+
     29 |   :?    |  exit with def as message  |      $VAR      |
     30 +---------+------------+---------------+----------------+
     31