When creating simple one-shot programs it can be very convenient to
see which variables are available at the prompt. The function
and its siblings
whos_line_format will show
different information about what is in memory, as the following shows.
str = "A random string"; who -variables -| *** local user variables: -| -| __nargin__ str
List currently defined variables matching the given patterns. Valid
pattern syntax is the same as described for the
If no patterns are supplied, all variables are listed.
By default, only variables visible in the local scope are displayed.
The following are valid options but may not be combined.
List variables in the global scope rather than the current scope.
The patterns are considered to be regular expressions when matching the
variables to display. The same pattern syntax accepted by
regexp function is used.
The next argument is treated as a filename. All variables found within the specified file are listed. No patterns are accepted when reading variables from a file.
If called as a function, return a cell array of defined variable names matching the given patterns.
See also: whos, isglobal, isvarname, exist, regexp.
Provide detailed information on currently defined variables matching the
given patterns. Options and pattern syntax are the same as for the
who command. Extended information about each variable is
summarized in a table with the following default entries.
Attributes of the listed variable. Possible attributes are:
Variable in local scope
Automatic variable. An automatic variable is one created by the
interpreter, for example
Variable of complex type.
Formal parameter (function argument).
Variable with global scope.
The name of the variable.
The logical size of the variable. A scalar is 1x1, a vector is 1xN or Nx1, a 2-D matrix is MxN.
The amount of memory currently used to store the variable.
The class of the variable. Examples include double, single, char, uint16, cell, and struct.
The table can be customized to display more or less information through
whos is called as a function, return a struct array of defined
variable names matching the given patterns. Fields in the structure
describing each variable are: name, size, bytes, class, global, sparse,
complex, nesting, persistent.
See also: who, whos_line_format.
Query or set the format string used by the command
A full format string is:
The following command sequences are available:
Prints attributes of variables (g=global, p=persistent, f=formal parameter, a=automatic variable).
Prints number of bytes occupied by variables.
Prints class names of variables.
Prints elements held by variables.
Prints variable names.
Prints dimensions of variables.
Prints type names of variables.
Every command may also have an alignment modifier:
Right alignment (default).
Column-aligned (only applicable to command %s).
width parameter is a positive integer specifying the minimum
number of columns used for printing. No maximum is needed as the field will
auto-expand as required.
balance are only available when the
column-aligned modifier is used with the command ‘%s’.
balance specifies the column number within the field width which will
be aligned between entries. Numbering starts from 0 which indicates the
left-min specifies the minimum field width to the
left of the specified balance column.
The default format is
" %a:4; %ln:6; %cs:16:6:1; %rb:12; %lc:-1;\n".
When called from inside a function with the
"local" option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
See also: whos.
Instead of displaying which variables are in memory, it is possible to determine if a given variable is available. That way it is possible to alter the behavior of a program depending on the existence of a variable. The following example illustrates this.
if (! exist ("meaning", "var")) disp ("The program has no 'meaning'"); endif
Return 1 if the name exists as a variable, 2 if the name is an
absolute file name, an ordinary file in Octave’s
path, or (after
appending ‘.m’) a function file in Octave’s
path, 3 if the
name is a ‘.oct’ or ‘.mex’ file in Octave’s
5 if the name is a built-in function, 7 if the name is a directory, or 103
if the name is a function not associated with a file (entered on
the command line).
Otherwise, return 0.
This function also returns 2 if a regular file called name
exists in Octave’s search path. If you want information about
other types of files, you should use some combination of the functions
If the optional argument type is supplied, check only for symbols of the specified type. Valid types are
Check only for variables.
Check only for built-in functions.
Check only for files and directories.
Check only for directories.
See also: file_in_loadpath, file_in_path, find_dir_in_path, stat.
Usually Octave will manage the memory, but sometimes it can be practical to remove variables from memory manually. This is usually needed when working with large variables that fill a substantial part of the memory. On a computer that uses the IEEE floating point format, the following program allocates a matrix that requires around 128 MB memory.
large_matrix = zeros (4000, 4000);
Since having this variable in memory might slow down other computations,
it can be necessary to remove it manually from memory. The
function allows this.
Delete the names matching the given patterns from the symbol table. The pattern may contain the following special characters:
Match any single character.
Match zero or more characters.
[ list ]
Match the list of characters specified by list. If the first
^, match all characters except those
specified by list. For example, the pattern ‘[a-zA-Z]’ will
match all lowercase and uppercase alphabetic characters.
For example, the command
clear foo b*r
clears the name
foo and all names that begin with the letter
b and end with the letter
clear is called without any arguments, all user-defined
variables (local and global) are cleared from the symbol table. If
clear is called with at least one argument, only the visible
names matching the arguments are cleared. For example, suppose you have
defined a function
foo, and then hidden it by performing the
foo = 2. Executing the command clear foo once
will clear the variable definition and restore the definition of
foo as a function. Executing clear foo a second time will
clear the function definition.
The following options are available in both long and short form
Clears all local and global user-defined variables and all functions from the symbol table.
Clears the variables that don’t match the following pattern.
Clears the function names and the built-in symbols names.
Clears the global symbol names.
Clears the local variable names.
Clears the class structure table and clears all objects.
The arguments are treated as regular expressions as any variables that match will be cleared.
With the exception of
exclusive, all long options can be used
without the dash as well.
Consolidate workspace memory in MATLAB. This function is provided for compatibility, but does nothing in Octave.
Information about a function or variable such as its location in the file system can also be acquired from within Octave. This is usually only useful during development of programs, and not within a program.
Display the contents of name which may be a file, function (m-file), variable, operator, or keyword.
type normally prepends a header line describing the category
of name such as function or variable; The -q option
suppresses this behavior.
If no output variable is used the contents are displayed on screen. Otherwise, a cell array of strings is returned, where each element corresponds to the contents of each requested function.
Display the type of each name. If name is defined from a function file, the full name of the file is also displayed.
See also: help, lookfor.
List the Octave specific files in directory dir. If dir is not specified then the current directory is used. If a return argument is requested, the files found are returned in the structure w.
See also: which.