February 27, 2013

A bashism a week: appending

The very well known appending operator += is a bashism commonly found in the wild. Even though it can be used for things such as adding to integers (when the variable is declared as such) or appending to arrays, it is usually used for appending to a string variable.

As I previously blogged about it, the appending operator bashism is only useful when programming for the bash shell.

Whenever you want to append a string to a variable, repeating the name of the variable is the portable way. I.e.
foo="${foo} bar"
# Instead of foo+=" bar", which is a bashism

See? Replacing the += operator is not rocket science.

Note: One should be aware that makefiles do have a += operator which is safe to use when appending to a make variable. But don't let this "exception" fool you: code in configure.ac and similar files is executed by the shell interpreter. So don't use the appending operator there.

1 comment:

  1. Recent mksh versions and AT&T ksh93 also implement += but the maxime is still: check what you’re using is actually supported!