Question

I’m trying to understand a bash script whose first four lines are:

#!/bin/sh
SCRIPT="`basename $0 | sed 's/\..*$//'`"
CONFIG=${1:-$HOME/.$SCRIPT}
DIR=${2:-$HOME/Documents}

I understand that the last two lines are doing parameter substitution on paths input as script arguments 1 and 2, but I’ve been unable to figure out how this works (e.g. here). What does the “:-” part mean? Sorry for the newbie question.

Answer 1

From man bash:

   ${parameter:-word}
          Use Default Values.  If parameter is unset or null, the expansion of word is substituted.  Other‐
          wise, the value of parameter is substituted.

Very easy to find, with man bash, and then /:-. The slash introduces a search, and :- is just the content to search for. Else, searching in bash can get very boring, because it is huge, but here it is the first hit.