Editing Scanco User Instructions (section)

===What is a symbol===
DCL can store information such as strings or integers in "symbols". DCL can also manipulate these symbols to create other symbols.
Symbols are primarily used to define short strings that replace long commands, perform certain calculations and replacements within DCL
procedures, hold status information.
<pre>
$ UR == "SET DEFAULT DISK4:[BONELAB.PROJECTS]"	!A short hand to change locations to the project disk.
$ UR :== SET DEFAULT DISK4:[BONELAB.PROJECTS]	!Another way to define the symbol without quotations.
$ x == 3	                                !Store the value 3 in the symbol x.
$ SHOW SYMBOL x                                 !Displays the value of the specified symbol, x.
$ DELETE/SYMBOL/GLOBAL x                        !Deletes the specified symbol, x.
</pre>
Selected symbols on the Scanco system:
<pre>
$ UD	                            !Changes to the data directory.
$ UR	                            !Changes to the projects directory.
$ DISKS	                            !Shows the current disk usage.
$ DEC                               !Opens a new DEC terminal.
$ EVE file.txt                      !Opens the file in the text editor.
$ AIX file.aim                      !Shows the processing log for an aim file. 
$ AIX -L file.aim                   !The "-L" is used to show the full processing log.
$ QUE	                            !Shows all entries in the queue.
$ GS file.ps or file.pdf            !Opens *.ps and *.pdf files in GhostScript.
$ CTHEADER file.isq or file.rsq     !Shows scan information for an *.isq or *.rsq file.
</pre>


To create a symbol, use the assignment statement ( = or = = ) or the
string assignment (:= or := =). The = versus == means local versus global assignment (same as := and :==). Local symbols are only available within the same procedure or procedure level (-> subroutines with CALL). For being available in another procedure or subroutine you need global symbols, otherwise there is no difference. When you use the string assignment, all
alphabetic characters are converted to uppercase and multiple spaces and
tabs are compressed to a single space. You can use string assignments to
create a symbol that represents a DCL command or to define a foreign
command (note that in either case, there is a 255-character limit). To
continue a character string over two lines in a string assignment, use a
single hyphen. 

For example:
 $ a := asdfasfdasdf        asdfasfafasdf
 $ b = "asdfasfdasdf        asdfasfafasdf"

 $ sh symb a
 A = "ASDFASFDASDF ASDFASFAFASDF"

 $ sh symb b
 B = "asdfasfdasdf        asdfasfafasdf"

The symbols are translated by single quotes. If the symbol translation is within a string, e.g.

<pre>
 $ WRITE OUTFILE "''AIMFILE'"
</pre>

then we need two single quotes '' to indicate that this is not a string that contains a real single quote.
It is a bit confusing that you only need at the beginning of a symbol two single quotes, but not in the end.

If you have the symbol just in a command, then 'AIMFILE' will do the job, e.g.

<pre>
 MYFILE := 'EVAL_DIR''AIMFILE'
</pre>

More about symbols you can find in the Open VMS User's Manual under 12.2 symbols, which can be viewed here: http://bone.wiki/images/c/c0/Open_VMS_User%27s_Manual.PDF

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