freebsd-skq/lib/libc/gen/wordexp.3

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.Dd September 30, 2015
.Dt WORDEXP 3
.Os
.Sh NAME
.Nm wordexp
.Nd "perform shell-style word expansions"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In wordexp.h
.Ft int
.Fn wordexp "const char * restrict words" "wordexp_t * restrict we" "int flags"
.Ft void
.Fn wordfree "wordexp_t *we"
.Sh DESCRIPTION
The
.Fn wordexp
function performs shell-style word expansion on
.Fa words
and places the list of words into the
.Va we_wordv
member of
.Fa we ,
and the number of words into
.Va we_wordc .
.Pp
The
.Fa flags
argument is the bitwise inclusive OR of any of the following constants:
.Bl -tag -width ".Dv WRDE_SHOWERR"
.It Dv WRDE_APPEND
Append the words to those generated by a previous call to
.Fn wordexp .
.It Dv WRDE_DOOFFS
As many
.Dv NULL
pointers as are specified by the
.Va we_offs
member of
.Fa we
are added to the front of
.Va we_wordv .
.It Dv WRDE_NOCMD
Disallow command substitution in
.Fa words .
See the note in
.Sx BUGS
before using this.
.It Dv WRDE_REUSE
The
.Fa we
argument was passed to a previous successful call to
.Fn wordexp
but has not been passed to
.Fn wordfree .
The implementation may reuse the space allocated to it.
.It Dv WRDE_SHOWERR
Do not redirect shell error messages to
.Pa /dev/null .
.It Dv WRDE_UNDEF
Report error on an attempt to expand an undefined shell variable.
.El
.Pp
The
.Vt wordexp_t
structure is defined in
.In wordexp.h
as:
.Bd -literal -offset indent
typedef struct {
	size_t	we_wordc;	/* count of words matched */
	char	**we_wordv;	/* pointer to list of words */
	size_t	we_offs;	/* slots to reserve in we_wordv */
} wordexp_t;
.Ed
.Pp
The
.Fn wordfree
function frees the memory allocated by
.Fn wordexp .
.Sh IMPLEMENTATION NOTES
The
.Fn wordexp
function is implemented using the undocumented
.Ic freebsd_wordexp
shell built-in command.
.Sh RETURN VALUES
The
.Fn wordexp
function returns zero if successful, otherwise it returns one of the following
error codes:
.Bl -tag -width ".Dv WRDE_NOSPACE"
.It Dv WRDE_BADCHAR
The
.Fa words
argument contains one of the following unquoted characters:
.Aq newline ,
.Ql | ,
.Ql & ,
.Ql \&; ,
.Ql < ,
.Ql > ,
.Ql \&( ,
.Ql \&) ,
.Ql { ,
.Ql } .
.It Dv WRDE_BADVAL
An error after successful parsing,
such as an attempt to expand an undefined shell variable with
.Dv WRDE_UNDEF
set in
.Fa flags .
.It Dv WRDE_CMDSUB
An attempt was made to use command substitution and
.Dv WRDE_NOCMD
is set in
.Fa flags .
.It Dv WRDE_NOSPACE
Not enough memory to store the result or
an error during
.Xr fork 2 .
.It Dv WRDE_SYNTAX
Shell syntax error in
.Fa words .
.El
.Pp
The
.Fn wordfree
function returns no value.
.Sh ENVIRONMENT
.Bl -tag -width ".Ev IFS"
.It Ev IFS
Field separator.
.El
.Sh EXAMPLES
Invoke the editor on all
.Pa .c
files in the current directory
and
.Pa /etc/motd
(error checking omitted):
.Bd -literal -offset indent
wordexp_t we;

wordexp("${EDITOR:-vi} *.c /etc/motd", &we, 0);
execvp(we.we_wordv[0], we.we_wordv);
.Ed
.Sh DIAGNOSTICS
Diagnostic messages from the shell are written to the standard error output
if
.Dv WRDE_SHOWERR
is set in
.Fa flags .
.Sh SEE ALSO
.Xr sh 1 ,
.Xr fnmatch 3 ,
.Xr glob 3 ,
.Xr popen 3 ,
.Xr system 3
.Sh STANDARDS
The
.Fn wordexp
and
.Fn wordfree
functions conform to
.St -p1003.1-2001 .
.Sh BUGS
The current
.Fn wordexp
implementation does not recognize multibyte characters other than UTF-8, since
the shell (which it invokes to perform expansions) does not.
.Sh SECURITY CONSIDERATIONS
Pathname generation may create output that is exponentially larger than the
input size.
.Pp
Although this implementation detects command substitution reliably for
.Dv WRDE_NOCMD ,
the attack surface remains fairly large.
Also, some other implementations
(such as older versions of this one)
may execute command substitutions even if
.Dv WRDE_NOCMD
is set.