There are a number of basic variable types, listed below. The type of a variable in a command or function is always cued by the name given in the command/function signature, which will either be (e.g, b for a boolean type) or start with (e.g., fposx for a float type) the first letter of the type’s name. Multiple instances of the same type in a command signature or FISH function are most often numbered (i1 i2 i3 … and so on).[1]


A catch-all for any (a) of the other types, excepting sym, shown here. Multiple instances in a command are numbered (a1 a2 a3 etc.). This type is also indicated when a specific combination of types is acceptable (for instance, the common case where a string s or an integer i may be supplied). When this is the case, the specific acceptable types are indicated in the explanatory text.


A Boolean value (b), with six valid expressions: on off true false yes no. If no value is found, a Boolean is assumed to be true. No value, on, true, and yes are all equivalent. off, false, and no are all equivalent. Multiple instances in a command are numbered (b1 b2 b3 etc.).


A real number (f), positive or negative. It may be written in scientific e notation. Multiple instances in a command are numbered (f1 f2 f3 etc.).


An index (ind), positive integer. Multiple instances in a command are numbered (ind1 ind2 ind3 etc.).


An integer (i), positive or negative. An integer cannot contain a decimal. Multiple instances in a command are numbered (i1 i2 i3 etc.).


A list (l), which is a changeable, ordered sequence of elements or items. Lists items are accessed by index. See Lists for more information.


A list of FISH values accessible by integer index.


A map (m) container of key-values pairs. See Maps for more information.


A number (n), for which either a flt or an int is valid. Multiple instances in a command are numbered (n1 n2 n3 etc.).


A string (s) of alphanumeric characters. Multiple instances in a command are numbered (s1 s2 s3 etc.). See Strings for more information.


A FISH symbol (name) — where name is the name of either a FISH variable or a FISH function.


A vector (v or v2 or v3) expressed as a matrix with one row. v2 and v3 denote that a 2D or 3D vector, respectively, is required. A plain “v” indicates that a vector of the same dimensionality as the code is required, that is, a 3D vector is required if the code is a 3D code, and a 2D vector is required if the code is a 2D code. In FLAC3D, v always indicates a 3D vector. When more than one vector of the same type in is required in a command these are distinguished with underscore-appended letters (v2_a v2_b or v_a v_b, etc.). See Vectors for more information.


A 2D vector.


[1]In some cases, multiple instances of a type in a single command may be demarcated differently if the variation enhances interpretability (for instance, fx fy fz). In other cases, they may be given “names” (imax, fradius, etc.) because they appear as arguments of one keyword but may be referenced in the explanatory text of another keyword (review the geometry generate cone command, for instance). In these cases the basic type is always indicated by the first letter — “i” for an int, “f” for a flt, and so on.