Skipping an iteration

You can use the continue keyword to skip the rest of the current iteration and start the next one, if there is any. For example, this code gets the size of every one of a set of directories, but it only runs du if the directory actually exists:

#!/bin/bash
dirs=(/bin /home /mnt /opt /usr)
for dir in "${dirs[@]}" ; do
    [[ -d $dir ]] || continue
    du -s -- "$dir"
done

The continue keyword skips to the next run of the loop if the directory does not exist. It uses the || control operator to do this; if you prefer, you could write it with a full if statement instead.

As well as testing for the general case of file existence or type, loop continuations such as this are a useful method for dealing with unexpanded glob patterns. Recall that with Bash's default settings, a glob pattern such as * will remain unexpanded if there are no matching files. This means that the glob can sometimes show up in unwanted places:

for tmp in /tmp/myapp/* ; do
    printf >&2 'Warning: file %s still exists\n' "$tmp"
done

If /tmp/myapp does not exist, or is empty, the preceding code will print:

Warning: file /tmp/myapp/* still exists

This is probably not what you wanted! We can handle the case of an unexpanded glob with a continue condition:

#!/bin/bash
for tmp in /tmp/myapp/* ; do
    [[ -e $tmp ]] || continue
    printf >&2 'Warning: file %s still exists\n' "$tmp"
done

This method skips any filename that does not actually exist, to handle the case of unexpanded globs. It works for multiple unexpanded globs in the same list, too.

You could also deal with this quirk using a find call instead, or with the nullglob option described in Chapter 5, Variables and Patterns .