How can I concatenate two variables? How do I append a string to a variable?
There is no (explicit) concatenation operator for strings (either literal or variable dereferences) in the shell; you just write them adjacent to each other:
If the right-hand side contains whitespace characters, it needs to be quoted:
1 var="$var1 - $var2"
If you're appending a string that doesn't "look like" part of a variable name, you just smoosh it all together:
Otherwise, braces or quotes may be used to disambiguate the right-hand side:
CommandSubstitution can be used as well. The following line creates a log file name logname containing the current date, resulting in names like e.g. log.2004-07-26:
1 logname="log.$(date +%Y-%m-%d)"
There's no difference when the variable name is reused, either. A variable's value (the string it holds) may be reassigned at will:
1 string="$string more data here"
Bash 3.1 has a new += operator that you may see from time to time:
It's generally best to use the portable syntax.