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Comprehensive bash parameter substitution docs @ [TLDP](http://www.tldp.org/LDP/abs/html/parameter-substitution.html)
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| #!/bin/bash | |
| default_value=-1 | |
| value=${1:-$default_value} | |
| echo value=$value |
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${parameter-default} and ${parameter:-default} are almost equivalent. The extra : makes a difference only when parameter has been declared, but is null. - TLDP