var(3) Variable Expansion Library var(3)NAME
OSSP var-- Variable Expansion
SYNOPSIS
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.
DESCRIPTION
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
(${name"["index"]}") expansion, plus optionally one or more post-opera‐
tions on the expanded value (${name":"op[":"op...]]"}").
The supported post-operations are length determination, case conver‐
sion, defaults, positive and negative alternatives, sub-strings, regu‐
lar expression based substitutions, character translations, and pad‐
ding. Additionally, a meta-construct plus arithmetic expressions for
index and range calculations allow (even nested) iterations over array
variable expansions (.."["..${name"[#+1]}".."]"..).
The actual variable value lookup is performed through a callback func‐
tion, so OSSP var can expand arbitrary values.
SYNTAX CONSTRUCTS
A string expanded through OSSP var can consist of arbitrary text char‐
acters plus one or more of the following special syntax constructs
which are expanded by OSSP var.
"\"NNN
Character with the octal value NNN (N: 0,...,7).
"\x"NN, "\x{"NNMM.."}"
Character with the hexadecimal value NN or the characters denoted
by grouped hexadecimal numbers NNMM... (N, M:
0,...,9,["aA"],...,["fF"]).
"\t", "\r", "\n"
Tabulator (TAB), Carriage Return (CR) and Newline (NL) character.
"\\", "\"x
Ordinary character "\" and x.
"$"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 (Nega‐
tive Alternative).
${name":o"start","[length]"}"
Substring of "$"name starting at position start with length charac‐
ters.
${name":o"start"-"[end]"}"
Substring of "$"name starting at position start and ending at posi‐
tion 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 occur‐
rences; 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 charac‐
ter 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 charac‐
ter ""#"" is expanded in body as the current loop index (0,... for
first variant and start,...,end with stepping step for second vari‐
ant). 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.
SYNTAX CONSTRUCTS (GRAMMAR)
All the variable syntax constructs supported by OSSP var follow the
same grammatical form. For completeness and reference reasons, the cor‐
responding 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 ::= '$'
DELIM_OPEN ::= '{'
DELIM_CLOSE ::= '}'
INDEX_OPEN ::= '['
INDEX_CLOSE ::= ']'
INDEX_MARK ::= '#'
NAME_CHARS ::= 'a'⎪...⎪'z'⎪'A'⎪...⎪'Z'⎪'0'⎪...⎪'9'
Notice that the grammar definitions of DELIM_INIT, DELIM_OPEN,
DELIM_CLOSE, INDEX_OPEN, INDEX_CLOSE, INDEX_MARK and NAME_CHARS corre‐
spond to the default syntax configuration only. They can be changed
through the API (see var_syntax_t).
APPLICATION PROGRAMMING INTERFACE (API)
The following is a detailed description of the OSSP var ISO-C language
Application Programming Interface (API):
TYPES
The OSSP var API consists of the following ISO-C data types:
var_rc_t
This is an exported enumerated integer type describing the return
code of all API functions. On success, every API function returns
"VAR_OK". On error, it returns "VAR_ERR_XXX". For a list of all
possible return codes see var.h. Their corresponding describing
text can be determined with function var_strerror.
var_t
This is an opaque data type representing a variable expansion con‐
text. Only pointers to this abstract data type are used in the
API.
var_config_t
This is an exported enumerated integer type describing configura‐
tion parameters for function var_config. Currently "VAR_CONFIG_SYN‐
TAX" for configuring the syntax via var_syntax_t, "VAR_CON‐
FIG_CB_VALUE" for configuring the callback for value lookups via
var_cb_value_t, and "VAR_CONFIG_CB_OPERATION" for configuring the
callback for custom value operation functions via var_cb_opera‐
tion_t are defined.
var_syntax_t
This is an exported structural data type describing the variable
construct syntax. It is passed to var_config on "VAR_CONFIG_SYNTAX"
and consists of the following members (directly corresponding to
the upper-case non-terminals in the grammar above):
char escape; /* default: '\\' */
char delim_init; /* default: '$' */
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"-ter‐
minate 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 call‐
back should return the number of entries in the array variable.
If var_idx is greater or equal zero, it should return the spec‐
ified 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 buf‐
fer 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 opera‐
tion functions. Such a callback function cb has to be of the fol‐
lowing 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 necessar‐
ily 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 opera‐
tion. 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 opera‐
tion 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 opera‐
tion 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 rea‐
son 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 out‐
put 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 unde‐
fined 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 addi‐
tional 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 describ‐
ing 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.
COMBINING UNESCAPING AND EXPANSION
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.
EXCEPTION HANDLING
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 sym‐
bol 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.
EXAMPLE (DEVELOPER)
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 vari‐
able constructs, unescaping new and unknown escape sequences). The
value lookup callback uses the process environment to resolve vari‐
ables.
#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 possi‐
bilities.
EXAMPLE (USER)
The following are a few sample use cases of OSSP var variable expan‐
sions. They all assume the default syntax configuration and the follow‐
ing 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
SEE ALSOpcre(3), regex(7), OSSP val (Value Access), OSSP ex (Exception Han‐
dling).
HISTORY
OSSP var was initially written by Peter Simons <simons@crypt.to> in No‐
vember 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.
02-Oct-2005 VAR 1.1.3 var(3)
