AWKA-ELMREF(5)

NAME

awka-elmref - Awka API Reference for use with Awka-ELM libraries.

DESCRIPTION
Awka is a translator of AWK programs to ANSI-C code, and a library (libawka.a) against which the code is linked to create executables. Awka is described in the awka manpage.

The Extended Library Methods (ELM) provide a way of adding new functions to the AWK language, so that they appear in your AWK code as if they were builtin functions such as substr() or index(). The awka-elm manpage contains an introduction to Awka-ELM.

This page lists the available data structures, definitions, functions and macros provided by libawka.h that you may use in creating C libraries that link with awka-generated code.

I have broken the page into the following main sections: BASIC VARIABLE METHODS, ARRAY METHODS, BUILTIN FUNCTIONS, I/O METHODS, REGULAR EXPRESSION METHODS. So, without further ado...

BASIC VARIABLE METHODS

Data Structures a_VAR typedef struct {
  double dval; /* the variable's numeric value */
  char * ptr; /* pointer to string, array or RE structure */
  unsigned int slen; /* length of string ptr as per strlen */
  unsigned int allc; /* space mallocated for string ptr */
  char type; /* records current cast of variable */
  char type2; /* double-typed variable flag, explained later. */
  char temp; /* TRUE if a temporary variable */ } a_VAR; The a_VAR structure is used to store everything related to AWK variables. This includes those named & used in your program, and transient variables created to return values from functions and other operations like string concatenation. As such, this structure is ubiquitous throughout libawka and awka-generated code. The type value is set to one of a number of #define values, described in the Defines paragraph below. Many functions and macros exist for working with the contents of a_VARs - see the Functions & Macros paragraph for details. a_VARARG typedef struct {
  a_VAR *var[256];
  int used; } a_VARARG; This structure is typically used to pass variable numbers of a_VARs to functions. Up to 256 a_VARs may be referenced by an a_VARARG, and the used value contains the number of a_VARs present. struct gvar_struct struct gvar_struct {
  char *name;
  a_VAR *var; }; Provides a mapping of the global variable names in an AWK script to pointers to their a_VAR structures. Internal Libawka Variables a_VAR * a_bivar[a_BIVARS] This array contains all the AWK internal variables, such as ARGV, ARGV, CONVFMT, ENVIRON and so on, along with $0 and the field variables $1..$n. a_BIVARS is a define, as are the identities of which element in the array belongs to which variable. Again, look for functions that manage these variables rather than working with them directly if possible. extern struct gvar_struct *_gvar; This is actually created & populated by the translated C code generated by awka, rather than by libawka.a. It is a NULL-terminated array of the gvar_struct structure defined earlier in this page, and contains the names of all global variables in an AWK script, mapped to their a_VAR structures. Defines

a_VARNUL - the type value of an a_VAR if the variable is unused.
a_VARDBL - the type value for an a_VAR cast to a number.
a_VARSTR - type where the a_VAR has been cast to a string.
a_VARARR - type where the a_VAR contains an array.
a_VARREG - type where the a_VAR contains a regular expression.
a_VARUNK - type where the a_VAR is a string, but could also be a
         number. Variables populated by getline, the FILENAME variable,
         and elements of an array created by split(), are all of this
         special type.

a_DBLSET - for a string a_VAR that has been read in context as a number, the
         type2 flag is set to this #define to prevent the string-to-number
         conversion being done again.
a_STRSET - the opposite of the above. The variable is a number, has been read
         as a string, hence the value of ptr is current, and the type2
         flag is set to this #define.

a_BIVARS provides the number of elements in the a_bivar[] array.

a_ARGC, a_ARGIND, a_ARGV, a_CONVFMT, a_ENVIRON, a_FILENAME, a_FNR, a_FS, a_NF, a_NR, a_OFMT, a_OFS, a_ORS, a_RLENGTH, a_RS, a_RSTART, a_RT, a_SUBSEP, a_DOL0, a_DOLN, a_FIELDWIDTHS, a_SAVEWIDTHS, a_SORTTYPE provide indexes to which elements in the a_bivar[] array are for which AWK internal variable.

Functions & Macros awka_getd(a_VAR *) This macro calls the awka_getdval() function, appending the calling file & line number for debug purposes. It read-casts the variable to a number, and returns the double value of the variable. By read-cast, we mean that if the variable is a string it remains so, but dval is set, and type2 is set to a_DBLSET. But if the a_VAR is a regular expression, the re structure is dropped and the variable converted to a number. If you're not sure whether an a_VAR you're about to read is a number, and you want to read it as one, simply call awka_getd(varname) - its the easiest way. awka_getd1(a_VAR *) Same as awka_getd, except this will be faster if the a_VAR * is a variable. Do not use this if the a_VAR * is a function call return value, as it'll call the function several times! In this case, use awka_getd() instead. awka_gets(a_VAR *) Similar to awka_getd(), this read-casts an a_VAR to a string, and returns the character array pointed to by ptr. awka_gets1(a_VAR *) Use this where the a_VAR * is a variable, not a function call that returns an a_VAR *, for faster performance. awka_getre(a_VAR *) Write-casts the a_VAR * to a regular expression, and returns the pointer to the awka_regexp structure. Write-cast means that the existing contents of the variable are dropped in favour of the new contents. static char *awka_strcpy(a_VAR *var, char *str) This function sets var to string type, and copies to it the contents of str. It returns a pointer to var->ptr. a_VAR *awka_varcpy(a_VAR *va, a_VAR *vb) This function copies the contents of scalar a_VAR *vb to scalar a_VAR *va, and returns a pointer to va. double awka_varcmp(a_VAR *va, a_VAR *vb) This function compares the contents of the two scalar variables, and returns 0 if the variables are equal, -1 if va is less than vb, or 1 if va is greater. Numerical comparison is used where possible, otherwise string. a_VAR *awka_vardup(a_VAR *va) This function creates a new a_VAR *, copies the contents of va, and returns a pointer to the new structure. awka_varinit(a_VAR *) A macro that takes a NULL a_VAR *, mallocs space for it, and initialises it to a_VARNUL. void awka_killvar(a_VAR *) Frees all memory used by the a_VAR, except the structure itself. static a_VAR * awka_argv() You can use a_bivar[a_ARGV] directly when reading the value of elements in the array, but when you want to write to the array, use the above function instead, as it will make sure the changes are recognised elsewhere in libawka. static a_VAR * awka_argc() You can use a_bivar[a_ARGC] directly when reading its value, but when you want to write to it, use the above function instead, as it will make sure the change is recognised elsewhere in libawka.

ARRAY METHODS

Data Structures & Variables
These are strictly internal to the array module within libawka. If you need functionality other than that provided by the array functions, I recommend creating your own custom array data structures and interface functions, otherwise you could cause serious problems. The structure definitions are too lengthy to list here, and the foolhardy may find them in lib/array.h within the awka distribution.

Defines a_ARR_TYPE_NULL The 'type' of an array that has not been initialised, or has been deleted.
a_ARR_TYPE_SPLIT The 'type' of an array populated by the split() builtin function.
a_ARR_TYPE_HSH The 'type' of arrays populated within the AWK script, eg. arr["pigs"] = cows.

a_ARR_CREATE When searching arrays, specifies that an element is to be created if it doesn't already exist in the array.
a_ARR_QUERY When searching arrays, this will not create a new element if it doesn't already exist.
a_ARR_DELETE In an array search, this flag will cause the element to be deleted from the array.

Functions void awka_arraycreate( a_VAR *var, char type ); Allocates an array structure of type type, makes var->ptr point to it, and sets var->type to a_VARARR. The type argument may be one of a_ARR_TYPE_NULL, a_ARR_TYPE_SPLIT or a_ARR_TYPE_HSH, according to how the array will be populated. void awka_arrayclear( a_VAR *var ); Assumes var is an a_VARARR, this deletes the contents of the array structure pointed to by var->ptr. a_VAR * awka_arraysearch1( a_VAR *v, a_VAR *element, char create, int set ); Searches array variable v for index element. If it does not exist, and create is a_ARR_CREATE, a new element in the array for this value will be added. If the element is found (or created) and create is not a_ARR_DELETE, the function will return a pointer to the a_VAR for that element. For a_ARR_DELETE, the element will be deleted from the array. The set value should be FALSE. a_VAR * awka_arraysearch( a_VAR *v, a_VARARG *va, char create ); Searches array variable v as per awka_arraysearch1(), except that this works with multiple index subscripts (eg, arr[x, y]). double awka_arraysplitstr( char *str, a_VAR *v, a_VAR *fs, int max ); The AWK builtin split() function. It splits str into array variable v, based on fs, up to max number of fields. If fs is NULL, then a_bivar[a_FS] will be used. Otherwise fs may contain an empty string, a single-character string, or a regular expression. The number of fields created in v is returned. int awka_arrayloop( a_ListHdr *ah, a_VAR *v ); This function implements the "for (i in j)" feature in AWK. You provide ah, making sure it is initialised to zeroes. The best way to understand how to call this function is to type:
  awka 'BEGIN { for (i in j) x = j[i]; }' and see what is generated as a result. You don't have to understand the a_ListHdr structure or sub-structures to use this function. int awka_arraynext( a_VAR *v, a_ListHdr *ah, int pos ); Given that ah has been populated by a call to awka_arrayloop(), this function copies the (string or integer) element at position pos in the list to v, then returns pos+1, or zero if there are no more elements in the array list. void awka_alistfree( a_ListHdr *ah ); Frees the last list element in ah. void awka_alistfreeall( a_ListHdr *ah ); Frees all memory held by ah, and sets its contents to zero/NULL. a_VAR * awka_dol0(int set); The best means of accessing the $0 a_VAR, as it updates its contents with any pending changes. Make set zero if you're reading the value of $0, but if you want to set $0, make it 1. a_VAR * awka_doln(int fld, int set); This function returns the a_VAR * of the $1..$n variable identified by fld, updating the field array with any refreshed $0 contents first if necessary. If you want to read the value of $fld, make set zero, otherwise it should be 1.

BUILTIN FUNCTIONS

These are documented in lib/builtin.h in the awka distribution. You can call any of the builtin functions as often as you like. Those that return a_VAR's also provide a keep flag that, if TRUE, will return a variable that you must free, otherwise they will use a temporary variable that you don't have to worry about freeing, but will be reused elsewhere sooner or later. The functions should be pretty much as you'd expect them, except that many require an a_VARARG as input, and we haven't discussed how to create one - we will now. a_VARARG * awka_arg0(char);
a_VARARG * awka_arg1(char, a_VAR *);
a_VARARG * awka_arg2(char, a_VAR *, a_VAR *);
a_VARARG * awka_arg3(char, a_VAR *, a_VAR *, a_VAR *); a_VARARG * awka_vararg(char, a_VAR *var, ...); These functions populate & return a pointer to an a_VARARG structure. The char argument, if TRUE, will make you responsible for freeing the structure, otherwise it'll be a temporary one that libawka will manage. awka_arg0() will return an empty structure (ie. no args), awka_arg1() will have one a_VAR * in it, and so on. Where you want to put more than four a_VAR *'s inside an a_VARARG, you can call awka_vararg with as many as you like, or if there's seriously a lot, maybe write your own loop of code to populate an a_VARARG - its not rocket science.

I/O METHODS

Data Structures & Variables _a_IOSTREAM typedef struct {
  char *name; /* name of output file or device */
  FILE *fp; /* file pointer */
  char *buf; /* input buffer */
  char *current; /* where up to in buffer */
  char *end; /* end of data in buffer */
  int alloc; /* size of input buffer */
  char io; /* input or output stream flag */
  char pipe; /* true/false */
  char interactive; /* whether from a /dev/xxx stream or not */ } _a_IOSTREAM; extern _a_IOSTREAM *_a_iostream; extern int _a_ioallc, _a_ioused; Controls input and output streams used by AWK's getline, print and printf builtin functions. The two int variables record the space allocated in the _a_iostream array, and the number of elements used, respectively. I list this information here in case you wish to create fread, fwrite and fseek functions for awka, as these will need low-level access to the streams. Functions a_VAR * awka_getline(char keep, a_VAR *target, char *input, int pipe, char main); As previously described, keep controls whether you want to be responsible for freeing the a_VAR the function returns or not. Moving on, target is the a_VAR to hold the line of data to be read (you provide this one). input is the name of the input file or command. pipe is TRUE if input is a command rather than a file, eg. "sort stuff | getline x". main should always be false. If input is NULL, getline will try to read from the file identified by a_bivar[a_FILENAME], or from the next element in the a_bivar[a_ARGV] array. I won't go into detail about awka_fflush, awka_close, awka_printf & so on, as these should be easy enough to understand and use, and the chances are you should use the native C variety anyway where possible.

REGULAR EXPRESSIONS

Ah, now we're in murky water indeed, as awka inherited its RE library from Libc, and treats it like a magical black box that does its bidding. Want my advice? Treating the RE library & structure like a black box is a wise thing to do, as its ugly-looking stuff.

Ok, we know that when an a_VAR has been set to a_VARREG, its ptr value will point to an awka_regexp structure. Do we need to know what's in this structure? I don't think so. What we do need are the functions that help us compile and execute regular expressions. Oops, getting ahead of myself. RE's are like C programs, they need to be compiled before they can be used to search strings. This basically is a parsing of the RE pattern into a tree structure that is easier to navigate while searching, and is a one-off task. awka_getre(a_VAR *) This macro is the easiest method of creating & compiling a regexp. Providing you've set the a_VAR to the string value of the re pattern, this macro call works a treat. a_VAR *awka_match(char keep, char fcall, a_VAR *va, a_VAR *rva); This function is the implementation of AWK's match() function, and is the most simple way of evaluating an RE against a string. keep is as previously discussed, fcall should be set to TRUE if you want a_bivar[a_RSTART] and a_bivar[a_RLENGTH] to be set, otherwise FALSE, va contains the string, and rva contains the regular expression. The numerical a_VAR returned is 1 on success, zero on failure. I was going to describe the lower-level methods of compiling and matching against RE's, but when I looked at it, there seemed to be a lot of complexity for no real gain in functionality. All you get is the ability to avoid using a_VAR structures to manage the regular expressions, and honestly I don't see what you'd gain from this given how much more complexity you'd have to deal with.

NOTES

I haven't described all of the functions available in libawka.h, not by any means. But I have tried to avoid functions that are really only meant for internal use, or that are only needed by translated code and should be done in other ways by library code. In the same way I've avoided describing structures that were intended to remain privy to a module within libawka, and you really shouldn't need to tamper with them.

Any questions at all, or suggestions for improving this page, let me know via andrewsumner@yahoo.com. Make sure you preface any message title with the word "awka" so I know its not spam.

SEE ALSO
awka(1), awka-elm(5).