Mastering Bash

The colon character (:)

The colon does actually nothing except expanding arguments and performing redirection. It can be handy in cycles and tests to actually do nothing if a condition is met. It is also interesting to see how it can be used to evaluate a series of variables using the parameter substitution:

#!/bin/bashx=32y=5: ${x?} ${y?} ${z?}And now let's execute it:zarrelli:~$ ./test-variable.sh./test-variable.sh: line 5: z: parameter null or not set

Here is a bite on redirection:

zarrelli:~$ echo "012345679" > test.colon.2zarrelli:~$ ls -lah test.colon.2-rw-r--r-- 1 zarrelli zarrelli 10 Feb 19 14:18 test.colon.2zarrelli:~$ : > test.colon.2zarrelli:~$ ls -lah test.colon.2-rw-r--r-- 1 zarrelli zarrelli 0 Feb 19 14:18 test.colon.2

So, what ...