You often may need to compare one version of a file to an earlier one or check one file against a reference file. Linux provides several tools for doing this, depending on how deep a comparison you need to make.

Bash functions, unlike functions in most programming languages do not allow you to return a value to the caller. When a bash function ends its return value is its status: zero for success, non-zero for failure. To return values, you can set a global variable with the result, or use command substitution, or you can pass in the name of a variable to use as the result variable. The examples below describe these different mechanisms.

If you ever need to download an entire Web site, perhaps for off-line viewing, wget can do the job—for example:

If you're used to a "standard" *NIX shell you may not be familiar with bash's array feature. Although not as powerful as similar constructs in the P languages (Perl, Python, and PHP) and others, they are often quite useful.