Substitution patterns

A substitution pattern is a structure (defined in interp.h) :

typedef struct SUBST_PAT {
    char        orig;
    subst_delim delim;
    pfi_char    F;
} subst_pat;

Here delim is a delimiter structure :

typedef struct SUBST_DELIM {
    char        begin;
    char        end;
} subst_delim;

and F is a pfi_char function :

typedef void    (*pfi_char)(char *, char **, flow_data *);

For instance when we use string variables (cf. 4.4) the members begin and end of delim (the underlying delimiter structure) are respectively [ and ], the member orig of the substitution pattern is $, and F is a function that replaces the name of the string variable by its contents.

Five substitution patterns are recognized by the interpreter :

#() : this is used to substitute arguments inside command files or programs (cf. 4.2).

%() : this is used to insert floating point numbers (cf. 4.3.2).

!() : this is used to insert integers (cf. 4.3.2).

$() : this is used to insert character strings defined by question files (cf. 4.8.3 and 8).

$[] : this is used to insert the content of string variables (cd. 4.4).

The corresponding substitution patterns are Subst_Pat[0] to Subst_Pat[4] (they are defined in the function default_Subst_Pat in interp.c).

It is possible to use nested substitution : for instance $[XX%(i+$[V])__!(x$(2))] is correct.