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.\" This file is part of wordsplit -*- nroff -*-
.\" Copyright (C) 2009-2019 Sergey Poznyakoff
.\"
.\" Wordsplit is free software; you can redistribute it and/or modify
.\" it under the terms of the GNU General Public License as published by
.\" the Free Software Foundation; either version 3, or (at your option)
.\" any later version.
.\"
.\" Wordsplit is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public License
.\" along with wordsplit.  If not, see <http://www.gnu.org/licenses/>.
.\"
.TH WORDSPLIT 3 "July 9, 2019" "WORDSPLIT" "Wordsplit User Reference"
.SH NAME
wordsplit \- split string into words 
.SH SYNOPSIS
.B #include <wordsplit.h>
.sp
\fBint wordsplit (const char *\fIs\fB,\
 wordsplit_t *\fIws\fB, int \fIflags\fB);\fR
.sp
\fBint wordsplit_len (const char *\fIs\fB,\
 \fBsize_t \fIlen\fR,\
 \fBwordsplit_t *\fIp\fB,\
 int \fIflags\fB);
.sp 
\fBvoid wordsplit_free (wordsplit_t *\fIp\fB);\fR
.sp
\fBvoid wordsplit_free_words (wordsplit_t *\fIws\fB);\fR
.sp
\fBvoid wordsplit_getwords (wordsplit_t *\fIws\fB,\
 int *\fIwordc\fB, char ***\fIwordv\fB);
.sp
\fBvoid wordsplit_perror (wordsplit_t *\fIws\fB);\fR
.sp
\fBconst char *wordsplit_strerror (wordsplit_t *\fIws\fB);\fR
.sp
\fBvoid wordsplit_clearerr (wordsplit_t *\fIws\fB);\fR
.SH DESCRIPTION
The function \fBwordsplit\fR splits the string \fIs\fR into words
using a set of rules governed by \fIflags\fR.  Depending on
\fIflags\fR, the function performs the following operations:
whitespace trimming, tilde expansion, variable expansion, quote
removal, command substitution, and path expansion.  On success,
\fBwordsplit\fR returns 0 and stores the words found in the member
\fBws_wordv\fR and the number of words in the member \fBws_wordc\fR.
On error, a non-zero error code is returned.
.PP
The function \fBwordsplit_len\fR acts similarly, except that it
accesses only first \fBlen\fR bytes of the string \fIs\fR, which is
not required to be null-terminated.
.PP
When no longer needed, the resources allocated by a call to one of
these functions must be freed using
.BR wordsplit_free .
.PP
The function
.B wordsplit_free_words
frees only the memory allocated for elements of
.I ws_wordv
after which it resets
.I ws_wordv to
.B NULL
and 
.I ws_wordc
to zero.
.PP
The usual calling sequence is:
.PP
.EX
wordsplit_t ws;
int rc;

if (wordsplit(s, &ws, WRDSF_DEFFLAGS)) {
    for (i = 0; i < ws.ws_wordc; i++) {
        /* do something with ws.ws_wordv[i] */
    }
}
wordsplit_free(&ws);
.EE
.PP
Notice, that \fBwordsplit_free\fR must be called after each invocation
of \fBwordsplit\fR or \fBwordsplit_len\fR, even if it resulted in
error.
.PP
The function
.B wordsplit_getwords
returns in \fIwordv\fR an array of words, and in \fIwordc\fR the number
of elements in \fIwordv\fR.  The array can be used after calling
.BR wordsplit_free .
The caller becomes responsible for freeing the memory allocated for
each element of the array and the array pointer itself.
.PP
The function
.B wordsplit_perror
prints error message from the last invocation of \fBwordsplit\fR.  It
uses the function pointed to by the
.I ws_error
member.  By default, it outputs the message on the standard error.
.PP
For more sophisticated error reporting, the function
.B wordsplit_strerror
can be used.  It returns a pointer to the string describing the error.
The caller should treat this pointer as a constant string.  It should
not try to alter or deallocate it.
.PP
The function
.B wordsplit_clearerr
clears the error condition associated with \fIws\fR.
.SH INCREMENTAL MODE
In incremental mode \fBwordsplit\fR parses one word per invocation.
It returns \fBWRDSF_OK\fR on success and \fBWRDSF_NOINPUT\fR when 
entire input string has been processed.
.PP
This mode is enabled if the flag \fBWRDSF_INCREMENTAL\fR is set in
the \fIflags\fR argument.  Subsequent calls to \fBwordsplit\fR must
have \fBNULL\fR as first argument.  Each successful
call will return exactly one word in \fBws.ws_wordv[0]\fR.
.PP
An example usage:
.PP
.EX
wordsplit_t ws;
int rc;
flags = WRDSF_DEFFLAGS|WRDSF_INCREMENTAL;

for (rc = wordsplit(s, &ws, flags); rc == WRDSF_OK;
     rc = wordsplit(NULL, &ws, flags)) {
     process(ws.ws_wordv[0]);
}     

if (rc != WRDSE_NOINPUT)
     wordsplit_perror(&ws);

wordsplit_free(&ws);
.EE
.SH OPTIONS
The number of flags is limited to 32 (the width of \fBuint32_t\fR data
type).  By the time of this writing each bit is already occupied by a
corresponding flag. However, the number of features \fBwordsplit\fR
provides requires still more. Additional features can be requested by
setting a corresponding \fIoption bit\fR in the \fBws_option\fR field
of the \fBstruct wordsplit\fR argument. To inform wordsplit functions
that this field is initialized the \fBWRDSF_OPTIONS\fR flag must be set.
.PP
Option symbolic names begin with \fBWRDSO_\fR. They are discussed in
detail in the subsequent chapters.
.SH EXPANSION
Expansion is performed on the input after it has been split into
words. The kinds of expansion to be performed are controlled by the
appropriate bits set in the \fIflags\fR argument.  Whatever expansion
kinds are enabled, they are always run in the order described in this
section.
.SS Whitespace trimming
Whitespace trimming removes any leading and trailing whitespace from
the initial word array.  It is enabled by the
.B WRDSF_WS
flag.  Whitespace trimming is enabled automatically if the word
delimiters (\fIws_delim\fR member) contain whitespace characters
(\fB\(dq \\t\\n\(dq\fR), which is the default.
.SS Variable expansion
Variable expansion replaces each occurrence of
.BI $ NAME
or
.BI ${ NAME }
with the value of the variable \fINAME\fR.  It is enabled by default
and can be disabled by setting the \fBWRDSF_NOVAR\fR flag.  The caller
is responsible for supplying the table of available variables.  Two
mechanisms are provided: environment array and a callback function.
.PP
Environment array is a \fBNULL\fR-terminated array of variables,
stored in the \fIws_env\fR member.  The \fBWRDSF_ENV\fR flag must be
set in order to instruct \fBwordsplit\fR to use this array.
.PP
By default, elements of the \fIws_env\fR array have the form
.IR NAME = VALUE .
An alternative format is enabled by the
.B WRDSF_ENV_KV
flag.  When it is set, each variable is described by two consecutive
elements in the array:
.IR ws_env [ n ]
containing the variable name, and
.IR ws_env [ "n+1" ]
containing its value. If the latter is \fBNULL\fR, the corresponding
variable is undefined.
.PP
More sophisticated variable tables can be implemented using 
callback function.  The \fIws_getvar\fR member should be set to point
to that function and \fBWRDSF_GETVAR\fR flag must be set.  The
function itself shall be defined as
.PP
.EX
int getvar (char **ret, const char *var, size_t len, void *clos);
.EE
.PP
The function shall look up the variable identified by the first
\fIlen\fR bytes of the string \fIvar\fR.  If the variable is found,
the function shall store a copy of its value (allocated using
\fBmalloc\fR(3)) in the memory location pointed to by \fBret\fR, and
return \fBWRDSE_OK\fR.  If the variable is not found, the function shall
return \fBWRDSE_UNDEF\fR.  Otherwise, a non-zero error code shall be
returned.
.PP
If \fIws_getvar\fR returns
.BR WRDSE_USERERR ,
it must store the pointer to the error description string in
.BR *ret .
In any case (whether returning \fB0\fR or \fBWRDSE_USERERR\fR), the
data returned in \fBret\fR must be allocated using
.BR malloc (3).
.PP
If both
.I ws_env
and
.I ws_getvar
are used, the variable is first looked up in
.IR ws_env .
If it is not found there, the 
.I ws_getvar
callback is invoked.
This order is reverted if the \fBWRDSO_GETVARPREF\fR option is set.
.PP
During variable expansion, the forms below cause
.B wordsplit
to test for a variable that is unset or null.  Omitting the
colon results in a test only for a variable that is unset.
.TP
.BI ${ variable :- word }
.BR "Use Default Values" .
If \fIvariable\fR is unset or null, the expansion of \fIword\fR is substituted.
Otherwise, the value of \fIvariable\fR is substituted.
.TP
.BI ${ variable := word }
.BR "Assign Default Values" .
If \fIvariable\fR is unset or null, the expansion of \fIword\fR is
assigned to \fIvariable\fR.  The value of \fIvariable\fR is then substituted.
.TP
.BI ${ variable :? word }
.BR "Display Error if Null or Unset" .
If \fIvariable\fR is null or unset, the expansion of \fIword\fR (or a
message to that effect if word is not present) is output using
.IR ws_error .
Otherwise, the value of \fIvariable\fR is substituted.
.TP
.BI ${ variable :+ word }
.BR "Use Alternate Value" .
If \fIvariable\fR is null or unset, nothing is substituted, otherwise the
expansion of \fIword\fR is substituted.
.PP
Unless the above forms are used, a reference to an undefined variable
expands to empty string.  Three flags affect this behavior.  If the
\fBWRDSF_UNDEF\fR flag is set, expanding undefined variable triggers
a \fBWRDSE_UNDEF\fR error.  If the \fBWRDSF_WARNUNDEF\fR flag is set,
a non-fatal warning is emitted for each undefined variable.  Finally,
if the \fBWRDSF_KEEPUNDEF\fR flag is set, references to undefined
variables are left unexpanded.
.PP
If two or three of these flags are set simultaneously, the behavior is
undefined.
.SS Positional argument expansion
\fIPositional arguments\fR are special parameters that can be
referenced in the input string by their ordinal number.  The numbering
begins at \fB0\fR.  The syntax for referencing positional arguments is
the same as for the variables, except that argument index is used
instead of the variable name.  If the index is between 0 and 9, the
\fB$\fIN\fR form is acceptable.  Otherwise, the index must be enclosed
in curly braces: \fB${\fIN\fB}\fR.
.PP
During argument expansion, references to positional arguments are
replaced with the corresponding values.
.PP
Argument expansion is requested by the \fBWRDSO_PARAMV\fR option bit.
The NULL-terminated array of variables shall be supplied in the
.I ws_paramv
member.  The
.I ws_paramc
member shall be initialized to the number of elements in
.IR ws_paramv .
.PP
Setting the \fBWRDSO_PARAM_NEGIDX\fR option together with
\fBWRDSO_PARAMV\fR enables negative positional argument references.
A negative reference has the form \fB${-\fIN\fB}\fR.  It is expanded
to the value of the argument with index \fB\fIws_paramc\fR \- \fIN\fR.
.SS Quote removal
During quote removal, single or double quotes surrounding a sequence
of characters are removed and the sequence itself is treated as a
single word.  Characters within single quotes are treated verbatim.
Characters within double quotes undergo variable expansion and
backslash interpretation (see below).
.PP
Recognition of single quoted strings is enabled by the
\fBWRDSF_SQUOTE\fR flag.  Recognition of double quotes is enabled by
the \fBWRDSF_DQUOTE\fR flag.  The macro \fBWRDSF_QUOTE\fR enables both.
.SS Backslash interpretation
Backslash interpretation translates unquoted
.I escape sequences
into corresponding characters.  An escape sequence is a backslash followed
by one or more characters.  By default, each sequence \fB\\\fIC\fR
appearing in unquoted words is replaced with the character \fIC\fR.  In
doubly-quoted strings, two backslash sequences are recognized:
\fB\\\\\fR translates to a single backslash, and \fB\\\(dq\fR
translates to a double-quote.
.PP
Two flags are provided to modify this behavior.  If
.I WRDSF_CESCAPES
flag is set, the following escape sequences are recognized:
.sp
.nf
.ta 8n 18n 42n
.ul
	Sequence	Expansion	ASCII
	\fB\\\\\fR	\fB\\\fR	134
	\fB\\\(dq\fR	\fB\(dq\fR	042
	\fB\\a\fR	audible bell	007	
	\fB\\b\fR	backspace	010
	\fB\\f\fR	form-feed	014
	\fB\\n\fR	new line	012
	\fB\\r\fR	charriage return	015
	\fB\\t\fR	horizontal tabulation	011
	\fB\\v\fR	vertical tabulation	013
.fi
.sp
The sequence \fB\\x\fINN\fR or \fB\\X\fINN\fR, where \fINN\fR stands
for a two-digit hex number is replaced with ASCII character \fINN\fR.
The sequence \fB\\0\fINNN\fR, where \fINNN\fR stands for a three-digit
octal number is replaced with ASCII character whose code is \fINNN\fR.
.PP
The \fBWRDSF_ESCAPE\fR flag allows the caller to customize escape
sequences.  If it is set, the \fBws_escape\fR member must be
initialized.  This member provides escape tables for unquoted words
(\fBws_escape[0]\fR) and quoted strings (\fBws_escape[1]\fR).  Each
table is a string consisting of an even number of characters.  In each
pair of characters, the first one is a character that can appear after
backslash, and the following one is its translation.  For example, the
above table of C escapes is represented as 
\fB\(dq\\\\\\\\"\\"a\\ab\\bf\\fn\\nr\\rt\\tv\\v\(dq\fR.
.PP
It is valid to initialize \fBws_escape\fR elements to zero.  In this
case, no backslash translation occurs.
.PP
Interpretation of octal and hex escapes is controlled by the following
bits in \fBws_options\fR:
.TP
.B WRDSO_BSKEEP_WORD
When an unrecognized escape sequence is encountered in a word,
preserve it on output.  If that bit is not set, the backslash is
removed from such sequences.
.TP
.B WRDSO_OESC_WORD
Handle octal escapes in words.
.TP
.B WRDSO_XESC_WORD
Handle hex escapes in words.
.TP
.B WRDSO_BSKEEP_QUOTE
When an unrecognized escape sequence is encountered in a doubly-quoted
string, preserve it on output.  If that bit is not set, the backslash is
removed from such sequences.
.TP
.B WRDSO_OESC_QUOTE
Handle octal escapes in doubly-quoted strings.
.TP
.B WRDSO_XESC_QUOTE
Handle hex escapes in doubly-quoted strings.
.SS Command substitution
During \fIcommand substitution\fR, each word is scanned for commands.
Each command found is executed and replaced by the output it creates.
.PP
The syntax is:
.PP
.RS +4
.BI $( command )
.RE
.PP
Command substitutions may be nested.
.PP
Unless the substitution appears within double quotes, word splitting and
pathname expansion are performed on its result.
.PP
To enable command substitution, the caller must initialize the
.I ws_command
member with the address of the substitution function and make sure the
.B WRDSF_NOCMD
flag is not set.
.PP
The substitution function should be defined as follows:
.PP
.RS +4
\fBint \fIcommand\fB\
 (char **\fIret\fB,\
 const char *\fIcmd\fB,\
 size_t \fIlen,\fB\
 char **\fIargv\fB,\
 void *\fIclos\fB);\fR
.RE
.PP
On input, the first \fIlen\fR bytes of \fIcmd\fR contain the command
invocation as it appeared between
.BR $( " and " ),
with all expansions performed. 
.PP
The \fIargv\fR parameter contains the command 
line split into words using the same settings as the input \fIws\fR structure.
.PP
The \fIclos\fR parameter supplies user-specific data, passed in the
\fIws_closure\fR member).
.PP
On success, the function stores a pointer to the
output string in the memory location pointed to by \fIret\fR and
returns \fBWRDSE_OK\fR (\fB0\fR).  On error, it must return one of the
error codes described in the section 
.BR "ERROR CODES" .
If 
.BR WRDSE_USERERR ,
is returned, a pointer to the error description string must be stored in
.BR *ret .
.PP
When \fBWRDSE_OK\fR or \fBWRDSE_USERERR\fR is returned, the
data stored in \fB*ret\fR must be allocated using
.BR malloc (3).
.SS Tilde and pathname expansion
Both expansions are performed if the
.B WRDSF_PATHEXPAND
flag is set.
.PP
.I Tilde expansion
affects any word that begins with an unquoted tilde
character (\fB~\fR).  If the tilde is followed immediately by a slash,
it is replaced with the home directory of the current user (as
determined by his \fBpasswd\fR entry).  A tilde alone is handled the
same way.  Otherwise, the characters between the tilde and first slash
character (or end of string, if it doesn't contain any) are treated as
a login name. and are replaced (along with the tilde itself) with the
home directory of that user.  If there is no user with such login
name, the word is left unchanged.
.PP
During
.I pathname expansion
each unquoted word is scanned for characters 
.BR * ", " ? ", and " [ .
If any of these appears, the word is considered a \fIpattern\fR (in
the sense of
.BR glob (3))
and is replaced with an alphabetically sorted list of file names matching the
pattern.
.PP
If no matches are found for a word
and the \fIws_options\fR member has the
.B WRDSO_NULLGLOB
bit set, the word is removed.
.PP
If the \fBWRDSO_FAILGLOB\fR option is set, an error message is output
for each such word using
.IR ws_error .
.PP
When matching a pattern, the dot at the start of a name or immediately
following a slash must be matched explicitly, unless 
the \fBWRDSO_DOTGLOB\fR option is set.
.SH LIMITING THE NUMBER OF WORDS
The maximum number of words to be returned can be limited by setting
the \fBws_maxwords\fR member to the desired count, and setting the
\fBWRDSO_MAXWORDS\fR option, e.g.:
.sp
.EX
struct wordsplit ws;
ws.ws_maxwords = 3;
ws.ws_options = WRDSO_MAXWORDS;
wordsplit(str, &ws, WRDSF_DEFFLAGS|WRDSF_OPTIONS);
.EE
.PP
If the actual number of words in the expanded input is greater than
the supplied limit, the trailing part of the input will be returned in
the last word. For example, if the input to the above fragment were
\fBNow is the time for all good men\fR, then the returned words would be:
.sp
.EX
"Now"
"is"
"the time for all good men"
.EE
.SH WORDSPLIT_T STRUCTURE
The data type \fBwordsplit_t\fR has three members that contain
output data upon return from \fBwordsplit\fR or \fBwordsplit_len\fR,
and a number of members that the caller can initialize on input in
order to customize the function behavior.  For each input member there
is a corresponding flag bit, which must be set in the \fIflags\fR argument
in order to instruct the \fBwordsplit\fR function to use the member.
.SS OUTPUT
.TP
.BI size_t " ws_wordc"
Number of words in \fIws_wordv\fR.  Accessible upon successful return
from \fBwordsplit\fR.
.TP
.BI "char ** " ws_wordv
Array of resulting words.  Accessible upon successful return
from \fBwordsplit\fR.
.PP
The caller should not attempt to free or reallocate \fIws_wordv\fR or
any elements thereof, nor to modify \fIws_wordc\fR.
.PP
To store away the words for use after freeing \fIws\fR with
.BR wordsplit_free ,
the caller should use
.BR wordsplit_getwords .
It is more effective than copying the contents of
.I ws_wordv
manually.
.TP
.BI "size_t " ws_wordi
Total number of words processed. This field is intended for use with
.B WRDSF_INCREMENTAL
flag. If that flag is not set, the following relation holds:
.BR "ws_wordi == ws_wordc - ws_offs" .
.TP
.BI "int " ws_errno
Error code, if the invocation of \fBwordsplit\fR or
\fBwordsplit_len\fR failed.  This is the same value as returned from
the function in that case.
.TP
.BI "char *" ws_errctx
On error, context in which the error occurred.  For
.BR WRDSE_UNDEF ,
it is the name of the undefined variable.  For
.B WRDSE_GLOBERR 
- the pattern that caused error.
.sp
The caller should treat this member as
.BR "const char *" .
.PP
The following members are used if the variable expansion was requested
and the input string contained an
.B Assign Default Values
form (\fB${\fIvariable\fB:=\fIword\fB}\fR).
.TP
.BI "char **" ws_envbuf
Modified environment.  It follows the same arrangement as \fIws_env\fR
on input (see the \fBWRDSF_ENV_KV\fR flag).  If \fIws_env\fR was NULL (or
\fBWRDSF_ENV\fR was not set), but the \fIws_getvar\fR callback was
used, the \fIws_envbuf\fR array will contain only the modified variables.
.TP
.BI "size_t " ws_envidx
Number of entries in
.IR ws_envbuf .
.PP
If positional parameters were used (see the \fBWRDSO_PARAMV\fR option)
and any of them were modified during processing, the following two
members supply the modified parameter array.
.TP
.BI "char ** " ws_parambuf
Array of positional parameters.
.TP
.BI "size_t " ws_paramidx
Number of positional parameters.
.SS INPUT
.TP
.BI "size_t " ws_offs
If the
.B WRDSF_DOOFFS
flag is set, this member specifies the number of initial elements in
.I ws_wordv
to fill with NULLs.  These elements are not counted in the returned
.IR ws_wordc .
.TP
.BI "size_t " ws_maxwords
Maximum number of words to return. For this field to take effect, the
\fBWRDSO_MAXWORDS\fR option and \fBWRDSF_OPTIONS\fR flag must be set.
For a detailed discussion, see the chapter
.BR "LIMITING THE NUMBER OF WORDS" .
.TP
.BI "int " ws_flags
Contains flags passed to wordsplit on entry.  Can be used as a
read-only member when using \fBwordsplit\fR in incremental mode or
in a loop with
.B WRDSF_REUSE
flag set.
.TP
.BI "int " ws_options
Additional options used when
.B WRDSF_OPTIONS
is set.
.TP
.BI "const char *" ws_delim
Word delimiters.  If initialized on input, the 
.B WRDSF_DELIM
flag must be set.  Otherwise, it is initialized on entry to
.B wordsplit
with the string \fB\(dq \\t\\n\(dq\fR.
.TP
.BI "const char *" ws_comment
A zero-terminated string of characters that begin an inline comment.
If initialized on input, the
.B WRDSF_COMMENT
flag must be set.  By default, it's value is \fB\(dq#\(dq\fR.
.TP
.BI "const char *" ws_escape [2]
Escape tables for unquoted words (\fBws_escape[0]\fR) and quoted
strings (\fBws_escape[1]\fR).  These are used to translate escape
sequences (\fB\\\fIC\fR) into characters.  Each table is a string
consisting of even number of characters.  In each pair of characters,
the first one is a character that can appear after backslash, and the
following one is its representation.  For example, the string
\fB\(dqt\\tn\\n\(dq\fR translates \fB\\t\fR into horizontal
tabulation character and \fB\\n\fR into newline.
.B WRDSF_ESCAPE
flag must be set if this member is initialized.
.TP
.BI "void (*" ws_alloc_die ") (wordsplit_t *)"
This function is called when
.B wordsplit
is unable to allocate memory and the
.B WRDSF_ENOMEMABRT
flag was set.  The default function prints a
message on standard error and aborts.  This member can be used
to customize error handling.  If initialized, the 
.B WRDSF_ALLOC_DIE
flag must be set.
.TP
.BI "void (*" ws_error ") (const char *, ...)"
Pointer to function used for error reporting.  The invocation
convention is the same as for
.BR printf (3).  
The default function formats and prints the message on the standard
error.

If this member is initialized, the
.B WRDSF_ERROR
flag must be set.
.TP
.BI "void (*" ws_debug ") (const char *, ...)"
Pointer to function used for debugging output.  By default it points
to the same function as
.BR ws_error .
If initialized, the
.B WRDSF_DEBUG
flag must be set.
.TP
.BR "const char **" ws_env
A \fBNULL\fR-terminated array of environment variables.  It is used
during variable expansion.  If set, the
.B WRDSF_ENV
flag must be set.  Variable expansion is enabled only if either
.B WRDSF_ENV
or
.B WRDSF_GETVAR
(see below) is set, and 
.B WRDSF_NOVAR
flag is not set.

Each element of 
.I ws_env
must have the form \fB\(dq\fINAME\fB=\fIVALUE\fR, where \fINAME\fR is
the name of the variable, and \fIVALUE\fR is its value.
Alternatively, if the \fBWRDSF_ENV_KV\fR flag is set, each variable is
described by two elements of 
.IR ws_env :
one containing variable name, and the next one with its
value.
.TP
.BI "int (*" ws_getvar ") (char **ret, const char *var, size_t len, void *clos)"
Points to the function that will be used during variable expansion for
environment variable lookups.
This function is used if the variable expansion is enabled (i.e. the
.B WRDSF_NOVAR
flag is not set), and the \fBWRDSF_GETVAR\fR flag is set.
.sp
If both 
.B WRDSF_ENV
and
.B WRDSF_GETVAR
are set, the variable is first looked up in the
.I ws_env
array and, if not found there,
.I ws_getvar
is called.  If the \fBWRDSO_GETVARPREF\fR option is set, this order is
reverted.
.sp
The name of the variable is specified by the first \fIlen\fR bytes of
the string \fIvar\fR.  The \fIclos\fR parameter supplies the
user-specific data (see below the description of \fIws_closure\fR
member) and the \fBret\fR parameter points to the memory location
where output data is to be stored.  On success, the function must
store there a pointer to the string with the value of the variable and
return 0.  On error, it must return one of the error codes described
in the section 
.BR "ERROR CODES" .
If \fIws_getvar\fR returns
.BR WRDSE_USERERR ,
it must store the pointer to the error description string in
.BR *ret .
In any case (whether returning \fB0\fR or \fBWRDSE_USERERR\fR), the
data returned in \fBret\fR must be allocated using
.BR malloc (3).
.TP
.BI "void *" ws_closure
Additional user-specific data passed as the last argument to
.I ws_getvar
or
.I ws_command
(see below).  If defined, the
.B WRDSF_CLOSURE
flag must be set.
.TP
\fBint (*\fIws_command\fB)\
 (char **ret,\
 const char *cmd,\
 size_t len,\
 char **argv,\
 void *clos)\fR
Pointer to the function that performs command substitution.  It treats
the first \fIlen\fR bytes of the string \fIcmd\fR as a command
(whatever it means for the caller) and attempts to execute it.  On
success, a pointer to the string with the command output is stored
in the memory location pointed to by \fBret\fR and \fB0\fR is
returned.  On error,
the function must return one of the error codes described in the section
.BR "ERROR CODES" .
If \fIws_command\fR returns
.BR WRDSE_USERERR ,
it must store the pointer to the error description string in
.BR *ret .
In any case (whether returning \fB0\fR or \fBWRDSE_USERERR\fR), the
data returned in \fBret\fR must be allocated using
.BR malloc (3).

The parameter \fBargv\fR contains the command split into
words using the same settings as the input \fIws\fR structure, with
command substitution disabled.

The \fIclos\fR parameter supplies user-specific data (see the
description of \fIws_closure\fR member).
.PP
The following two members are consulted if the \fBWRDSO_PARAMV\fR
option is set.  They provide an array of positional parameters.
.TP
.BI "char const **" ws_paramv
Positional parameters.  These are accessible in the input string using
the notation \fB$\fIN\fR or \fB${\fIN\fB}\fR, where \fIN\fR is the
0-based parameter number.
.TP
.BI "size_t " ws_paramc
Number of positional parameters.
.SH FLAGS
The following macros are defined for use in the \fBflags\fR argument.
.TP
.B WRDSF_DEFFLAGS
Default flags.  This is a shortcut for:

\fB(WRDSF_NOVAR |\
 WRDSF_NOCMD |\
 WRDSF_QUOTE |\
 WRDSF_SQUEEZE_DELIMS |\
 WRDSF_CESCAPES)\fR,

i.e.: disable variable expansion and quote substitution, perform quote
removal, treat any number of consecutive delimiters as a single
delimiter, replace \fBC\fR escapes appearing in the input string with
the corresponding characters.
.TP
.B WRDSF_APPEND
Append the resulting words to the array left from a previous call to
\fBwordsplit\fR.
.TP
.B WRDSF_DOOFFS
Insert
.I ws_offs
initial
.BR NULL s
in the array
.IR ws_wordv .
These are not counted in the returned
.IR ws_wordc .
.TP
.B WRDSF_NOCMD
Don't do command substitution.  The \fBWRDSO_NOCMDSPLIT\fR option set
together with this flag prevents splitting command invocations
into separate words (see the \fBOPTIONS\fR section).
.TP
.B WRDSF_REUSE
The parameter \fIws\fR resulted from a previous call to
\fBwordsplit\fR, and \fBwordsplit_free\fR was not called. Reuse the
allocated storage.
.TP
.B WRDSF_SHOWERR
Print errors using
.BR ws_error .
.TP
.B WRDSF_UNDEF
Consider it an error if an undefined variable is expanded.
.TP
.B WRDSF_NOVAR
Don't do variable expansion.  The \fBWRDSO_NOVARSPLIT\fR option set
together with this flag prevents variable references from being split
into separate words (see the \fBOPTIONS\fR section).
.TP
.B WRDSF_ENOMEMABRT
Abort on
.B ENOMEM
error.  By default, out of memory errors are treated as any other
errors: the error is reported using \fIws_error\fR if the
.B WRDSF_SHOWERR
flag is set, and error code is returned.  If this flag is set, the
.B ws_alloc_die
function is called instead.  This function is not supposed to return.
.TP
.B WRDSF_WS
Trim off any leading and trailing whitespace from the returned
words.  This flag is useful if the \fIws_delim\fR member does not
contain whitespace characters.
.TP
.B WRDSF_SQUOTE
Handle single quotes.
.TP
.B WRDSF_DQUOTE
Handle double quotes.
.TP
.B WRDSF_QUOTE
A shortcut for \fB(WRDSF_SQUOTE|WRDSF_DQUOTE)\fR.
.TP
.B WRDSF_SQUEEZE_DELIMS
Replace each input sequence of repeated delimiters with a single
delimiter.
.TP
.B WRDSF_RETURN_DELIMS
Return delimiters.
.TP
.B WRDSF_SED_EXPR
Treat
.BR sed (1)
expressions as words.
.TP
.B WRDSF_DELIM
.I ws_delim
member is initialized.
.TP
.B WRDSF_COMMENT
.I ws_comment
member is initialized.
.TP
.B WRDSF_ALLOC_DIE
.I ws_alloc_die
member is initialized.
.TP
.B WRDSF_ERROR
.I ws_error
member is initialized.
.TP
.B WRDSF_DEBUG
.I ws_debug
member is initialized.
.TP
.B WRDSF_ENV
.I ws_env
member is initialized.
.TP
.B WRDSF_GETVAR
.I ws_getvar member is initialized.
.TP
.B WRDSF_SHOWDBG
Enable debugging.
.TP
.B WRDSF_NOSPLIT
Don't split input into words.  This flag is is useful for side
effects, e.g. to perform variable expansion within a string.
.TP
.B WRDSF_KEEPUNDEF
Keep undefined variables in place, instead of expanding them to
empty strings.
.TP
.B WRDSF_WARNUNDEF
Warn about undefined variables.
.TP
.B WRDSF_CESCAPES
Handle \fBC\fR-style escapes in the input string.
.TP
.B WRDSF_CLOSURE
.I ws_closure
is set.
.TP
.B WRDSF_ENV_KV
Each two consecutive elements in the
.I ws_env
array describe a single variable:
.IR ws_env [ n ]
contains variable name, and
.IR ws_env [ "n+1" ]
contains its value.
.TP
.B WRDSF_ESCAPE
.I ws_escape
is set.
.TP
.B WRDSF_INCREMENTAL
Incremental mode.  Each subsequent call to \fBwordsplit\fR with
\fBNULL\fR as its first argument parses the next word from the input.
See the section
.B INCREMENTAL MODE
for a detailed discussion.
.TP
.B WRDSF_PATHEXPAND
Perform pathname and tilde expansion.  See the
subsection
.B "Pathname expansion"
for details.
.TP
.B WRDSF_OPTIONS
The
.I ws_options
member is initialized.
.SH OPTIONS
The
.I ws_options
member is consulted if the
.B WRDSF_OPTIONS
flag is set.  It contains a bitwise \fBOR\fR of one or more of the
following options:
.TP
.B WRDSO_NULLGLOB
Remove the words that produce empty string after pathname expansion.
.TP
.B WRDSO_FAILGLOB
Output error message if pathname expansion produces empty string.
.TP
.B WRDSO_DOTGLOB
During pathname expansion allow a leading period to be matched by
metacharacters.
.PP
.TP
.B WRDSO_BSKEEP_WORD
Backslash interpretation: when an unrecognized escape sequence is
encountered in a word, preserve it on output.  If that bit is not set,
the backslash is removed from such sequences.
.TP
.B WRDSO_OESC_WORD
Backslash interpretation: handle octal escapes in words.
.TP
.B WRDSO_XESC_WORD
Backslash interpretation: handle hex escapes in words.
.TP
.B WRDSO_BSKEEP_QUOTE
Backslash interpretation: when an unrecognized escape sequence is
encountered in a doubly-quoted string, preserve it on output.  If that
bit is not set, the backslash is removed from such sequences.
.TP
.B WRDSO_OESC_QUOTE
Backslash interpretation: handle octal escapes in doubly-quoted strings.
.TP
.B WRDSO_XESC_QUOTE
Backslash interpretation: handle hex escapes in doubly-quoted strings.
.TP
.B WRDSO_MAXWORDS
The \fBws_maxwords\fR member is initialized. This is used to control
the number of words returned by a call to \fBwordsplit\fR. For a
detailed discussion, refer to the chapter 
.BR "LIMITING THE NUMBER OF WORDS" .
.TP
.B WRDSO_NOVARSPLIT
When \fBWRDSF_NOVAR\fR is set, don't split variable references, even
if they contain whitespace.  E.g.
.B ${VAR:-foo bar}
will be treated as a single word.
.TP
.B WRDSO_NOCMDSPLIT
When \fBWRDSF_NOCMD\fR is set, don't split whatever looks like command
invocation, even if it contains whitespace.  E.g.
.B $(command arg)
will be treated as a single word.
.TP
.B WRDSO_PARAMV
Positional arguments are supplied in
.I ws_paramv
and
.IR ws_paramc .
See the subsection
.B Positional argument expansion
for a discussion.
.TP
.B WRDSO_PARAM_NEGIDX
Used together with \fBWRDSO_PARAMV\fR, this allows for negative
positional argument references.  A negative argument reference has the
form \fB${-\fIN\fB}\fR.  It is expanded to the value of the argument
with index \fB\fIws_paramc\fR \- \fIN\fR, i.e. \fIN\fRth if counting
from the end.
.SH "ERROR CODES"
.TP
.BR WRDSE_OK ", " WRDSE_EOF
Successful return.
.TP
.B WRDSE_QUOTE
Missing closing quote.  The \fIws_endp\fR points to the position in
the input string where the error occurred.
.TP
.B WRDSE_NOSPACE
Memory exhausted.
.TP
.B WRDSE_USAGE
Invalid wordsplit usage.
.TP
.B WRDSE_CBRACE
Unbalanced curly brace.
.TP
.B WRDSE_UNDEF
Undefined variable.  This error is returned only if the
\fBWRDSF_UNDEF\fR flag is set.
.TP
.B WRDSE_NOINPUT
Input exhausted.  This is not actually an error.  This code is returned
if \fBwordsplit\fR (or \fBwordsplit_len\fR) is invoked in incremental
mode and encounters end of input string.  See the section
.BR "INCREMENTAL MODE" .
.TP
.B WRDSE_PAREN
Unbalanced parenthesis.
.TP
.B WRDSE_GLOBERR
An error occurred during pattern matching.
.TP
.B WRDSE_USERERR
User-defined error.  Normally this error is returned by \fBws_getvar\fR or
\fBws_command\fR.  Use the function
.B wordsplit_strerror
to get textual description of the error.
.SH "RETURN VALUE"
Both
.B wordsplit
and
.B wordsplit_len
return \fB0\fR on success, and a non-zero error code on
error (see the section
.BR "ERROR CODES" ).
.PP
.B wordsplit_strerror
returns a pointer to the constant string describing the last error
condition that occurred in
.IR ws .
.SH EXAMPLE
The short program below implements a function that parses the
input string similarly to the shell.  All expansions are performed.
Default error reporting is used.
.PP
.EX
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <wordsplit.h>

/* Run command from \fIstr\fR (\fIlen\fR bytes long) and store its
   output in \fIret\fR.
   \fIargv\fR and \fIclosure\fR are not used.
   Return wordsplit error code.
 */
static int runcmd(char **ret, const char *str, size_t len,
                  char **argv, void *closure)
{
    FILE *fp;
    char *cmd;
    int c, lastc;
    char *buffer = NULL;
    size_t bufsize = 0;
    size_t buflen = 0;

    /* Convert to a null-terminated string for \fBpopen\fR(3) */
    cmd = malloc(len + 1);
    if (!cmd)
        return WRDSE_NOSPACE;
    memcpy(cmd, str, len);
    cmd[len] = 0;

    fp = popen(cmd, "r");
    if (!fp) {
        char buf[128];

        snprintf(buf, sizeof buf, "can't run %s: %s",
                 cmd, strerror(errno));
        *ret = strdup(buf);
        if (!*ret)
            return WRDSE_NOSPACE;
        else
            return WRDSE_USERERR;
    }

    /* Collect the output, reallocating \fIbuffer\fR as needed. */
    while ((c = fgetc(fp)) != EOF) {
        lastc = c;
        if (c == '\n')
            c = ' ';
        if (buflen == bufsize) {
            char *p;

            if (bufsize == 0)
                bufsize = 80;
            else
                bufsize *= 2;
            p = realloc(buffer, bufsize);
            if (!p) {
                free(buffer);
                free(cmd);
                return WRDSE_NOSPACE;
            }
            buffer = p;
        }
        buffer[buflen++] = c;
    }

    /* Tream off the trailing newline */
    if (buffer) {
        if (lastc == '\n')
            --buflen;
        buffer[buflen] = 0;
    }

    pclose(fp);
    free(cmd);

    /* Return the composed string. */
    *ret = buffer;
    return WRDSE_OK;
}

extern char **environ;

/* Parse \fIs\fR much as shell does.  Return array of words on
   succes, and NULL on error.
 */
char **shell_parse(char *s)
{
    wordsplit_t ws;
    size_t wc;
    char **wv;
    int rc;

    /* Initialize \fIws\fR */
    ws.ws_env = (const char **) environ;
    ws.ws_command = runcmd;
    /* Call \fBwordsplit\fR.  Let it report errors, if any. */
    rc = wordsplit(s, &ws,
                   WRDSF_QUOTE | WRDSF_SQUEEZE_DELIMS | WRDSF_PATHEXPAND
                   | WRDSF_SHOWERR);
    if (rc == WRDSE_OK)
        /* Store away the resulting words on success. */
        wordsplit_getwords(&ws, &wc, &wv);
    else
        wv = NULL;
    wordsplit_free(&ws);
    return wv;
}
.EE
.SH AUTHORS
Sergey Poznyakoff
.SH BUGS
Backtick command expansion is not supported.
.SH "BUG REPORTS"
Report bugs to <gray@gnu.org>.
.SH COPYRIGHT
Copyright \(co 2009-2019 Sergey Poznyakoff
.br
.na
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
.br
.ad
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.\" Local variables:
.\" eval: (add-hook 'write-file-hooks 'time-stamp)
.\" time-stamp-start: ".TH [A-Z_][A-Z0-9_]* [0-9] \""
.\" time-stamp-format: "%:B %:d, %:y"
.\" time-stamp-end: "\""
.\" time-stamp-line-limit: 20
.\" end:

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