OSSP var -- Variable Expansion
- Types:
- var_rc_t, var_t, var_config_t, var_syntax_t,
var_cb_value_t, var_cb_operation_t.
- Functions:
- var_create, var_destroy, var_config,
var_unescape, var_expand, var_formatv,
var_format, var_strerror.
- Variables:
- var_id.
OSSP var is a flexible, full-featured and fast variable construct
expansion library.
It supports a configurable variable construct syntax very similar to the style
found in many scripting languages (like "@"
name, ${
name"}", $(
name")", etc.) and provides both
simple scalar (${
name"}") and array
(${
name"["
index"]}") expansion, plus
optionally one or more post-operations on the expanded value (${
name":"
op[":"
op...]]"}").
The supported post-operations are length determination, case conversion,
defaults, positive and negative alternatives, sub-strings, regular expression
based substitutions, character translations, and padding. Additionally, a
meta-construct plus arithmetic expressions for index and range calculations
allow (even nested) iterations over array variable expansions
(.."["..${
name"[#+1]}".."]"..).
The actual variable value lookup is performed through a callback function, so
OSSP var can expand arbitrary values.
A string expanded through
OSSP var can consist of arbitrary text
characters plus one or more of the following special syntax constructs which
are expanded by
OSSP var.
- "\"NNN
- Character with the octal value NNN ( N: 0,...,7).
- "\x"NN, "\x{"NNMM.."}"
- Character with the hexadecimal value NN or the characters denoted
by grouped hexadecimal numbers NNMM... (N, M:
0,...,9,["aA"],...,["fF"]).
- "\t", "\r", "\n"
- Tabulator (TAB), Carriage Return (CR) and Newline (NL) character.
- "\\", "\"x
- Ordinary character "\" and x.
- "$"name, ${name"}"
- Contents of scalar variable name.
- ${name"["index"]""}"
- Contents of array variable name at position index. For
index full arithmetic expressions are allowed.
- ${name":#}"
- Length of "$"name.
- ${name":l}", ${name":u}"
- "$"name, converted to all lower-case or all
upper-case.
- ${name":-"word"}"
- If "$"name is not empty string and not undefined, then
"$" name, else word (Default Value).
- ${name":+"word"}"
- If "$"name is empty string, then empty string, else
word (Positive Alternative).
- ${name":*"word"}"
- If "$"name is not empty string, then empty string, else
word (Negative Alternative).
- ${name":o"start","[length]"}"
- Substring of "$"name starting at position start
with length characters.
- ${name":o"start"-"[end]"}"
- Substring of "$"name starting at position start
and ending at position end (inclusive).
- ${name":s/"pattern"/"string"/"["itg"]"}"
- "$"name after replacing characters matching
pattern with string. By default, case-sensitive regular
expression matching is performed and only the first occurrence of
pattern is replaced. Flag ""i"" switches to
case insensitive matching; flag ""t"" switches to
plain text pattern; flag ""g"" switches to
replacements of all occurrences; flag ""m"" switches
to multi-line matching (That is, change ""^"" and
""$"" from matching the start or end of the string to
matching the start or end of any line).
- ${name":y/"ochars"/"nchars"/}"
- "$"name after replacing all characters found in the
ochars character class by the corresponding character in the
nchars character class.
- ${name":p/"width"/"string"/"{"l","c","r"}"}"
- "$"name after padding to width with string.
Original contents of name is either left justified (flag
""l""), centered (flag ""c""), or
right justified (flag ""r"").
- ${name":%"func["("arg")"]"}"
- "$"name after passing it to an application-supplied
function func. The optional argument arg is passed to the
function, too. By default no such functions are defined.
- "["body"]",
"["body"]""{"
start","step","end"}"
- Repeat expansion of body as long as at least one array variable
does not expand to the empty string (first variant) or exactly (
end- start)/step times (second variant). In both
cases the character ""#"" is expanded in body
as the current loop index (0,... for first variant and
start,...,end with stepping step for second variant).
The ""#"" is usually used in the index of array
variable lookups. For start, step and end, full
arithmetic expressions are allowed. This loop construct can be nested,
too. In this case an inner loop is fully repeated for each iteration of
the outer loop. Additionally, arithmetic expressions are supported in both
start, step, end and index parts of variable
constructs in body.
All the variable syntax constructs supported by
OSSP var follow the same
grammatical form. For completeness and reference reasons, the corresponding
grammar is given in an extended BNF:
input ::= ( TEXT
⎪ variable
⎪ INDEX_OPEN input INDEX_CLOSE (loop_limits)?
)*
variable ::= DELIM_INIT (name⎪expression)
name ::= (NAME_CHARS)+
expression ::= DELIM_OPEN
(name⎪variable)+
(INDEX_OPEN num_exp INDEX_CLOSE)?
(':' command)*
DELIM_CLOSE
command ::= '-' (TEXT_EXP⎪variable)+
⎪ '+' (TEXT_EXP⎪variable)+
⎪ 'o' NUMBER ('-'⎪',') (NUMBER)?
⎪ '#'
⎪ '*' (TEXT_EXP⎪variable)+
⎪ 's' '/' (TEXT_PATTERN)+
'/' (variable⎪TEXT_SUBST)*
'/' ('m'⎪'g'⎪'i'⎪'t')*
⎪ 'y' '/' (variable⎪TEXT_SUBST)+
'/' (variable⎪TEXT_SUBST)*
'/'
⎪ 'p' '/' NUMBER
'/' (variable⎪TEXT_SUBST)*
'/' ('r'⎪'l'⎪'c')
⎪ '%' (name⎪variable)+
('(' (TEXT_ARGS)? ')')?
⎪ 'l'
⎪ 'u'
num_exp ::= operand
⎪ operand ('+'⎪'-'⎪'*'⎪'/'⎪'%') num_exp
operand ::= ('+'⎪'-')? NUMBER
⎪ INDEX_MARK
⎪ '(' num_exp ')'
⎪ variable
loop_limits ::= DELIM_OPEN
(num_exp)? ',' (num_exp)? (',' (num_exp)?)?
DELIM_CLOSE
NUMBER ::= ('0'⎪...⎪'9')+
TEXT_PATTERN::= (^('/'))+
TEXT_SUBST ::= (^(DELIM_INIT⎪'/'))+
TEXT_ARGS ::= (^(DELIM_INIT⎪')'))+
TEXT_EXP ::= (^(DELIM_INIT⎪DELIM_CLOSE⎪':'))+
TEXT ::= (^(DELIM_INIT⎪INDEX_OPEN⎪INDEX_CLOSE))+
DELIM_INIT ::= '$'
DELIM_OPEN ::= '{'
DELIM_CLOSE ::= '}'
INDEX_OPEN ::= '['
INDEX_CLOSE ::= ']'
INDEX_MARK ::= '#'
NAME_CHARS ::= 'a'⎪...⎪'z'⎪'A'⎪...⎪'Z'⎪'0'⎪...⎪'9'
Notice that the grammar definitions of DELIM_INIT, DELIM_OPEN, DELIM_CLOSE,
INDEX_OPEN, INDEX_CLOSE, INDEX_MARK and NAME_CHARS correspond to the default
syntax configuration only. They can be changed through the API (see
var_syntax_t).
The following is a detailed description of the
OSSP var ISO-C
language Application Programming Interface (API):
TYPES
The
OSSP var API consists of the following
ISO-C data types:
- var_rc_t
- This is an exported enumerated integer type describing the return code of
all API functions. On success, every API function returns
"VAR_OK". On error, it returns "VAR_ERR_XXX". For a
list of all possible return codes see var.h. Their corresponding
describing text can be determined with function var_strerror.
- var_t
- This is an opaque data type representing a variable expansion context.
Only pointers to this abstract data type are used in the API.
- var_config_t
- This is an exported enumerated integer type describing configuration
parameters for function var_config. Currently
"VAR_CONFIG_SYNTAX" for configuring the syntax via
var_syntax_t, "VAR_CONFIG_CB_VALUE" for configuring the
callback for value lookups via var_cb_value_t, and
"VAR_CONFIG_CB_OPERATION" for configuring the callback for
custom value operation functions via var_cb_operation_t are
defined.
- var_syntax_t
- This is an exported structural data type describing the variable construct
syntax. It is passed to var_config on "VAR_CONFIG_SYNTAX"
and consists of the following members (directly corresponding to the
upper-case non-terminals in the grammar above):
char escape; /* default: '\\' */
char delim_init; /* default: '$' */
char delim_open; /* default: '{' */
char delim_close; /* default: '}' */
char index_open; /* default: '[' */
char index_close; /* default: ']' */
char index_mark; /* default: '#' */
char *name_chars; /* default: "a-zA-Z0-9_" */
All members are single character constants, except for name_chars
which is a character class listing all valid characters. As an
abbreviation the construct " x"-"y" is
supported which means all characters from x to y (both
included) in the underlying character set.
- var_cb_value_t
- This is an exported function pointer type for variable value lookup
functions. Such a callback function cb has to be of the following
prototype:
var_rc_t * cb(var_t *var, void *ctx, const char
*var_ptr, size_t var_len, int var_idx, const char
**val_ptr, size_t * val_len, size_t *val_size);
This function will be called by var_expand internally whenever it has
to resolve the contents of a variable. Its parameters are:
- var_t *var
- This is the passed-through argument as passed to var_expand as the
first argument. This can be used in the callback function to distinguish
the expansion context or to resolve return codes, etc.
- void *ctx
- This is the passed-through argument as passed to var_config on
"VAR_CONFIG_CB_VALUE" as the forth argument. This can be used to
provide an internal context to the callback function through
var_expand.
- const char *var_ptr
- This is a pointer to the name of the variable whose contents
var_expand wishes to resolve. Please note that the string is NOT
necessarily terminated by a "NUL" ('"\0"') character.
If the callback function needs it "NUL"-terminated, it has to
copy the string into an a temporary buffer of its own and
"NUL"-terminate it there.
- size_t var_len
- This is the length of the variable name at var_ptr.
- int var_idx
- This determines which entry of an array variable to lookup. If the
variable specification that led to the execution of the lookup function
did not contain an index, zero (0) is provided by default as
var_idx. If var_idx is less than zero, the callback should
return the number of entries in the array variable. If var_idx is
greater or equal zero, it should return the specified particular entry. It
is up to the callback to decide what to return for an index not equal to
zero if the underlying variable is a scalar.
- const char **val_ptr
- This is a pointer to the location where the callback function should store
the pointer to the resolved value of the variable.
- size_t *val_len
- This is a pointer to the location where the callback function should store
the length of the resolved value of the variable.
- size_t *val_size
- This is a pointer to the location where the callback function should store
the size of the buffer that has been allocated to hold the value of the
resolved variable.
If no buffer has been allocated by the callback at all, because the variable
uses some other means of storing the contents -- as in the case of
getenv(3), where the system provides the buffer for the string --,
this should be set to zero (0).
In case a buffer size greater than zero is returned by the callback,
var_expand will make use of that buffer internally if possible. It
will also free(3) the buffer when it is not needed anymore, so it
is important that it was previously allocated with malloc(3) by the
callback.
The return code of the lookup function
cb is interpreted by
var_expand according to the following convention: "VAR_OK"
means success, that is, the contents of the variable has been resolved
successfully and the
val_ptr,
val_len, and
val_size
variables have been filled with appropriate values. A return code
"VAR_ERR_XXX" means that the resolving failed, such as a system
error or lack of resources. In the latter two cases, the contents of
val_ptr,
val_len and
val_size is assumed to be undefined.
Hence,
var_expand will not
free(3) any possibly allocated
buffers, the callback must take care of this itself.
If a callback returns the special "VAR_ERR_UNDEFINED_VARIABLE" return
code, the behavior of
var_expand depends on the setting of its
force_expand parameter. If
force_expand has been set,
var_expand will pass-through this error to the caller. If
force_expand has not been set,
var_expand will copy the
expression that caused the lookup to fail verbatim into the output buffer so
that an additional expanding pass may expand it later.
If the callback returns an "VAR_ERR_XXX",
var_expand will fail
with this return code. If the cause for the error can not be denoted by an
error code defined in
var.h, callback implementors should use the error
code "VAR_ERR_CALLBACK" (which is currently defined to -64). It is
guaranteed that no error code smaller than "VAR_ERR_CALLBACK" is
ever used by any
OSSP var API function, so if the callback implementor
wishes to distinguish between different reasons for failure, he subtract own
callback return codes from this value, i.e., return
("VAR_ERR_CALLBACK" -
n) (
n >= 0) from the callback
function.
- var_cb_operation_t
- This is an exported function pointer type for variable value operation
functions. Such a callback function cb has to be of the following
prototype:
var_rc_t * cb(var_t *var, void *ctx, const char
*op_ptr, size_t op_len, const char *arg_ptr, size_t
arg_len, const char * val_ptr, size_t val_len, const
char ** out_ptr, size_t * out_len, size_t *out_size);
This function will be called by var_expand internally whenever a
custom operation is used. Its parameters are:
- var_t *var
- This is the passed-through argument as passed to var_expand as the
first argument. This can be used in the callback function to distinguish
the expansion context or to resolve return codes, etc.
- void *ctx
- This is the passed-through argument as passed to var_config on
"VAR_CONFIG_CB_OPERATION" as the forth argument. This can be
used to provide an internal context to the callback function through
var_expand.
- const char *op_ptr
- This is a pointer to the name of the operation which var_expand
wishes to perform. Please note that the string is NOT necessarily
terminated by a "NUL" ('"\0"') character. If the
callback function needs it "NUL"-terminated, it has to copy the
string into an a temporary buffer of its own and "NUL"-terminate
it there.
- size_t op_len
- This is the length of the variable name at op_ptr.
- const char *arg_ptr
- This is a pointer to the optional argument string to the operation. If no
argument string or an empty argument string was supplied this is
"NULL".
- size_t arg_len
- This is the length of the arg_ptr.
- const char *val_ptr
- This is a pointer to the value of the variable which the operation wants
to adjust.
- size_t val_len
- This is the length of the val_ptr.
- const char **out_ptr
- This is a pointer to the location where the callback function should store
the pointer to the adjusted value.
- size_t *out_len
- This is a pointer to the location where the callback function should store
the length of the adjusted value of the variable.
- size_t *out_size
- This is a pointer to the location where the callback function should store
the size of the buffer that has been allocated to hold the adjusted value
of the variable.
If no buffer has been allocated by the callback at all, because the variable
uses some other means of storing the contents, this should be set to zero
(0).
In case a buffer size greater than zero is returned by the callback,
var_expand will make use of that buffer internally if possible. It
will also free(3) the buffer when it is not needed anymore, so it
is important that it was previously allocated with malloc(3) by the
callback.
FUNCTIONS
The
OSSP var API consists of the following
ISO-C functions:
- var_rc_t var_create(var_t **var);
- Create a new variable expansion context and store it into var.
- var_rc_t var_destroy(var_t *var);
- Destroy the variable expansion context var.
- var_rc_t var_config(var_t *var, var_config_t mode,
...);
- Configure the variable expansion context var. The variable argument
list depends on the mode identifier:
- "VAR_CONFIG_SYNTAX", var_syntax_t *syntax
- This overrides the syntax configuration in var with the one
provided in syntax. The complete structure contents is copied, so
the caller is allowed to immediately destroy syntax after the
var_config call. The default is the contents as shown above under
the type description of var_syntax_t.
- "VAR_CONFIG_CB_VALUE", var_cb_value_t cb, void
*ctx
- This overrides the value expansion in var. The default is
"NULL" for cb and ctx. At least "NULL"
for cb is not valid for proper operation of var_expand, so
the caller has to configure the callback before variable expansions can be
successfully performed.
- "VAR_CONFIG_CB_OPERATION", var_cb_operation_t cb, void
*ctx
- This provides a custom value operation function for var. The
default is "NULL" for cb and ctx which means no
custom operation is available.
- var_rc_t var_unescape(var_t *var, const char
*src_ptr, size_t src_len, char *dst_ptr, size_t
dst_len, int all);
- This expands escape sequences found in the input buffer
src_ptr/src_len. The dst_ptr/dst_len point to
a output buffer, into which the expanded data is copied if processing is
successful. The size of this buffer must be at least src_len+1
characters. The reason is that var_unescape always adds a
terminating "NUL" ('"\0"') character at the end of the
output buffer, so that you can use the result comfortably with other C
library routines. The supplied dst_ptr either has to point to a
pre-allocated buffer or is allowed to point to src_ptr (because the
unescaping operation is guaranteed to either keep the size or reduce the
size of the input).
The parameter all is a boolean flag that modifies the behavior of
var_unescape. If is set to true (any value except zero),
var_unescape will expand any escape sequences it sees, even
those that it does not know about. This means that
""\1"" will become "1", even though
""\1"" has no special meaning to var_unescape.
If all is set to false (the value zero), such escape sequences will
be copied verbatim to the output buffer.
The quoted pairs supported by var_unescape are
""\t"" (tabulator), ""\r""
(carriage return), ""\n"" (line feed),
""\NNN"" (octal value), ""\xNN""
(hexadecimal value), and ""\x{NNMM..}"" (grouped
hexadecimal values).
- var_rc_t var_expand(var_t *var, const char *src_ptr,
size_t src_len, char **dst_ptr, size_t *dst_len, int
force_expand);
- This is the heart of OSSP var. It expands all syntax constructs in
src_ptr/src_len and stores them in an allocated buffer
returned in dst_ptr/dst_len.
The output buffer dst_ptr/dst_len is allocated by
var_expand using the system call malloc(3), thus it is the
caller's responsibility to free(3) that buffer once it is no longer
used anymore. The output buffer for convenience reasons is always
"NUL"-terminated by var_expand, but this "NUL"
character is not counted for dst_len. The dst_len pointer
can be specified as "NULL" if you are not interested in the
output buffer length.
The force_expand flag determines how var_expand deals with
undefined variables (indicated by the callback function through the return
code "VAR_ERR_UNDEFINED_VARIABLE"). If it is set to true (any
value except zero), var_expand will fail with error code
"VAR_ERR_UNDEFINED_VARIABLE" whenever an undefined variable is
encountered. That is, it just passes-through the return code of the
callback function. If set to false (value zero), var_expand will
copy the expression it failed to expand verbatim into the output buffer,
in order to enable you to go over the buffer with an additional pass.
Generally, if you do not plan to use multi-pass expansion, you should set
force_expand to true in order to make sure no unexpanded variable
constructs are left over in the buffer.
If var_expand fails with an error, dst_ptr will point to
src_ptr and dst_len will contain the number of characters
that have been consumed from src_ptr before the error occurred. In
other words, if an error occurs, dst_ptr/dst_len point to
the last parsing location in src_ptr/src_len before the
error occurred. The only exceptions for this error semantics are: on
"VAR_ERR_INVALID_ARGUMENT" and "VAR_ERR_OUT_OF_MEMORY"
errors, dst_ptr and dst_len are undefined.
- var_rc_t var_formatv(var_t *var, char **dst_ptr, int
force_expand, const char *fmt, va_list ap);
- This is a high-level function on top of var_expand which expands
simple printf(3)-style constructs before expanding the complex
variable constructs. So, this is something of a combination between
sprintf(3) and var_expand.
It expands simple "%s" (string, type ""char
*""), "%d" (integer number, type
""int"") and "%c" (character, type
""int"") constructs in fmt. The values are
taken from the variable argument vector ap. After this expansion
the result is passed through var_expand by passing through the
var, dst_ptr and force_expand arguments. The final
result is a malloc(3)'ed buffer provided in dst_ptr which
the caller has to free(3) later.
- var_rc_t var_format(var_t *var, char **dst_ptr, int
force_expand, const char *fmt, ...);
- This is just a wrapper around var_formatv which translates the
variable argument list into "va_list".
- var_rc_t var_strerror(var_t *var, var_rc_t rc, char
** str);
- This can be used to map any var_rc_t return codes (as returned by
all the OSSP var API functions) into a clear-text message
describing the reason for failure in prose. Please note that errors coming
from the callback, such as "VAR_ERR_CALLBACK" and those based on
it, cannot be mapped and will yield the message ""unknown
error"".
VARIABLES
The
OSSP var API consists of the following
ISO-C exported
variables:
- var_id
- This is just a pointer to the constant string ""OSSP
var"". It is used as the first argument in ex_trow calls
if OSSP var is built with OSSP ex support. It then allows
the application to determine whether a caught exception was thrown by
OSSP var. See EXCEPTION HANDLING below for more
details.
For maximum power and flexibility, you usually want to combine
var_unescape and
var_expand. That is, you will want to use
var_unescape to turn all escape sequences into their real
representation before you call
var_expand for expanding variable
constructs. This way the user can safely use specials like
""\n"" or ""\t"" throughout the
template and achieve the desired effect. These escape sequences are
particularly useful if search-and-replace or transpose actions are performed
on variables before they are expanded. Be sure, though, to make the first
var_unescape pass with the
all flag set to false, or the routine
will also expand escape sequences like ""\1"", which might
have a special meaning (regular expression back-references) in the
var_expand pass to follow.
Once all known escape sequences are expanded, expand the variables with
var_expand. After that, you will want to have a second pass with
var_unescape and the flag
all set to true, to make sure all
remaining escape sequences are expanded. Also, the
var_expand pass
might have introduced now quoted pairs into the output text, which you need to
expand to get the desired effect.
OSSP var can be optionally built with support for exception handling via
OSSP ex (see http://www.ossp.org/pkg/lib/ex/). For this it has to be
configured with the GNU Autoconf option "--with-ex". The difference
then is that the
OSSP var API functions throw exceptions instead of
returning "VAR_ERR_XXX" return codes.
The thrown exceptions can be identified as
OSSP var exceptions by
checking the exception attribute
ex_class. It is the
OSSP var
API symbol
var_id for all
OSSP var exceptions. The
ex_object attribute is always "NULL". The
ex_value
attribute is the
var_rc_t which forced the throwing of the exception.
Exception throwing can be suppressed with
ex_shield only.
The following simple but complete program illustrates the full usage of
OSSP
var. It accepts a single argument on the command line and expands this in
three steps (unescaping known escape sequences, expanding variable constructs,
unescaping new and unknown escape sequences). The value lookup callback uses
the process environment to resolve variables.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "var.h"
static var_rc_t lookup(
var_t *var, void *ctx,
const char *var_ptr, size_t var_len, int var_idx,
const char **val_ptr, size_t *val_len, size_t *val_size)
{
char tmp[256];
if (var_idx != 0)
return VAR_ERR_ARRAY_LOOKUPS_ARE_UNSUPPORTED;
if (var_len > sizeof(tmp) - 1)
return VAR_ERR_OUT_OF_MEMORY;
memcpy(tmp, var_ptr, var_len);
tmp[var_len] = '\0';
if ((*val_ptr = getenv(tmp)) == NULL)
return VAR_ERR_UNDEFINED_VARIABLE;
*val_len = strlen(*val_ptr);
*val_size = 0;
return VAR_OK;
}
static void die(const char *context, var_t *var, var_rc_t rc)
{
char *error;
var_strerror(var, rc, &error);
fprintf(stderr, "ERROR: %s: %s (%d)\n", context, error, rc);
exit(1);
}
int main(int argc, char *argv[])
{
var_t *var;
var_rc_t rc;
char *src_ptr;
char *dst_ptr;
size_t src_len;
size_t dst_len;
var_syntax_t syntax = { '\\', '$', '{', '}', '[', ']', '#', "a-zA-Z0-9_" };
/* command line handling */
if (argc != 2)
die("command line", NULL, VAR_ERR_INVALID_ARGUMENT);
src_ptr = argv[1];
src_len = strlen(src_ptr);
fprintf(stdout, "input: \"%s\"\n", src_ptr);
/* establish variable expansion context */
if ((rc = var_create(&var)) != VAR_OK)
die("create context", NULL, rc);
if ((rc = var_config(var, VAR_CONFIG_SYNTAX, &syntax)) != VAR_OK)
die("configure syntax", var, rc);
if ((rc = var_config(var, VAR_CONFIG_CB_VALUE, lookup, NULL)) != VAR_OK)
die("configure callback", var, rc);
/* unescape known escape sequences (in place) */
if ((rc = var_unescape(var, src_ptr, src_len, src_ptr, src_len+1, 0)) != VAR_OK)
die("unescape known escape sequences", var, rc);
src_len = strlen(src_ptr);
fprintf(stdout, "unescaped: \"%s\"\n", src_ptr);
/* expand variable constructs (force expansion) */
if ((rc = var_expand(var, src_ptr, src_len, &dst_ptr, &dst_len, 1)) != VAR_OK) {
if (rc != VAR_ERR_INVALID_ARGUMENT && rc != VAR_ERR_OUT_OF_MEMORY) {
fprintf(stdout, "parsing: \"%s\"\n", dst_ptr);
fprintf(stdout, " %*s\n", dst_len, "^");
}
die("variable expansion", var, rc);
}
fprintf(stdout, "expanded: \"%s\"\n", dst_ptr);
/* unescape new and unknown escape sequences (in place) */
if ((rc = var_unescape(var, dst_ptr, dst_len, dst_ptr, dst_len+1, 1)) != VAR_OK)
die("unescape new and unknown escape sequences", var, rc);
fprintf(stdout, "output: \"%s\"\n", dst_ptr);
free(dst_ptr);
/* destroy variable expansion context */
if ((rc = var_destroy(var)) != VAR_OK)
die("destroy context", var, rc);
return 0;
}
Copy & paste the source code into a file
var_play.c (or use the
version already shipped with the
OSSP var source distribution), compile
it with
$ cc `var-config --cflags` \
-o var_play var_play.c \
`var-config --ldflags --libs`
and use it to play with the various
OSSP var variable expansion
possibilities.
The following are a few sample use cases of
OSSP var variable expansions.
They all assume the default syntax configuration and the following variable
definitions: "$foo=foo" (a scalar),
"$bar=<bar1,bar2,bar3,>" (an array),
"$baz=<baz1,baz2,baz3,>" (another array),
"$quux=quux" (another scalar),
"$name=<foo,bar,baz,quux>" (another scalar) and
"$empty=""" (another scalar).
Input Output
----------------------------- --------------
$foo foo
${foo} foo
${bar[0]} bar1
${${name[1]}[0]} bar1
${foo:u:y/O/U/:s/(.*)/<\1>/} <FUU>
${foo:u:y/O/U/:s/(.*)/<\1>/} <FUU>
${empty:-foo} foo
${foo:+yes}${foo:*no} yes
${empty:+yes}${empty:*no} no
${foo:p/6/./l} foo...
${foo:p/6/./r} ...foo
[${bar[#]}${bar[#+1]:+,}] bar1,bar2,bar3
[${bar[#-1]:+,}${bar[#]}] bar1,bar2,bar3
[${bar[#]}]{2,1,3} bar2bar3
[${bar[#]}]{1,2,3} bar1bar3
[${foo[#]}[${bar[#]}]]{1,,2} foo1bar1bar2bar3foo2bar1bar2bar3
pcre(3),
regex(7),
OSSP val (Value Access),
OSSP ex
(Exception Handling).
OSSP var was initially written by Peter Simons <simons@crypt.to> in
November 2001 under contract with the
OSSP sponsor
Cable &
Wireless. Its API and internal code structure was revamped in February
2002 by Ralf S. Engelschall <rse@engelschall.com> to fully conform to
the
OSSP library standards. Before its initial public release, Ralf S.
Engelschall in March 2002 finally added support for custom operations, the
formatting functionality, optional multi-line matching, etc.