Editing AmigaDOS (section)

===Local and global variables===
As any other DOS, Amiga deals with [[Variable (computer science)|environment variables]] as used in batch programming.

There are both global and local variables, and they are referred to with a dollar sign in front of the variable name, for example '''$myvar'''. Global variables are available system-wide; local variables are only valid in the current shell. In case of name collision, local variables have precedence over global variables. Global variables can be set using the command '''SetEnv''', while local variables can be set using the command '''Set'''. There are also the commands '''GetEnv''' and '''Get''' that can be used to print out global and local variables.

The examples below demonstrate simple usage:

<syntaxhighlight lang="doscon">
1> setenv foo blapp
1> echo $foo
blapp
1> set foo bar
1> echo $foo
bar
1> getenv foo
blapp
1> get foo
bar
1> type ENV:foo
blapp
1> setenv save foo $foo
1> type ENV:foo
bar
1> type ENVARC:foo
bar
</syntaxhighlight>
: If the <syntaxhighlight lang="doscon" inline>save</syntaxhighlight> flag of the <syntaxhighlight lang="doscon" inline>SetEnv</syntaxhighlight> command is set, this variable is saved permanently in <syntaxhighlight lang="doscon" inline>ENVARC:</syntaxhighlight> and remains available even after the current session has ended or the system has been restarted.

Global variables are kept as files in '''ENV:''', and optionally saved on disk in '''ENVARC:''' to survive reboot and [[power cycling]]. '''ENV:''' is by default an assign to RAM:Env, and ENVARC: is an assign to '''SYS:Prefs/Env-archive''' where SYS: refers to the [[Booting#Boot_device|boot device]]. On bootup, the content of ENVARC: is copied to ENV: for accessibility.

When programming AmigaDOS scripts, one must keep in mind that global variables are system-wide. All script-internal variables shall be set using local variables, or one risks conflicts over global variables between scripts. Also, global variables require filesystem access, which typically makes them slower to access than local variables.

Since ENVARC: is also used to store other system settings than just string variables (such as system settings, default icons and more), it tends to grow large over time, and copying everything over to ENV: located on RAM disk becomes expensive. This has led to alternative ways to set up ENV: by using dedicated [[ramdisk]] handlers that only copy files over from ENVARC: when the files are requested. Examples of such handlers are <ref>{{cite web|url=http://aminet.net/package/disk/misc/HappyENV |title=disk/misc/HappyENV.lha |publisher=Aminet |access-date=2016-07-15}}</ref> and.<ref>{{cite web|url=http://aminet.net/package/util/sys/envhandler |title=util/sys/envhandler.lha |publisher=Aminet |access-date=2016-07-15}}</ref> 

An example demonstrating creative abuse of global variables as well as '''Lab''' and '''Skip''' is the AmigaDOS variant of the infamous [[GOTO]].<ref>{{cite web|url=http://www.safalra.com/programming/amigados/universal-register-machine/|title=Code by Stephen Morley|access-date=April 5, 2016}}</ref>