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What does the following bash snippet do exactly? ${2:-${1}}
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- 1 means the first parameter passed to the function ( $1 or ${1} ) - # means the index of $1 , which, since $1 is an associative array, makes # the keys of $1. - * means the values of of the # keys in associate array $1.
1 "Standard output" output file descriptor. The expression 2>&1 copies file descriptor 1 to location 2 , so any output written to 2 ("standard error") in the execution environment goes to the same file originally described by 1 ("standard output").
Here are all the ways in which variables are substituted in Shell: ${variable} This command substitutes the value of the variable. ${variable:-word} If a variable is null or if it is not set, word is substituted for variable.
$1 means an input argument and -z means non-defined or empty. You're testing whether an input argument to the script was defined when running the script. Follow this answer to receive notifications.
"Use the second argument, but if none then the first one".
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