.\" SUCH DAMAGE.
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.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
-.\" $FreeBSD: src/bin/sh/sh.1,v 1.174 2011/07/10 15:02:25 jilles Exp $
+.\" $FreeBSD: src/bin/sh/sh.1,v 1.175 2011/11/05 21:56:45 jilles Exp $
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-.Dd August 21, 2011
+.Dd December 25, 2011
.Dt SH 1
.Os
.Sh NAME
The first letter of a variable name must not be numeric.
A parameter can also be denoted by a number
or a special character as explained below.
+.Pp
+Assignments are expanded differently from other words:
+tilde expansion is also performed after the equals sign and after any colon
+and usernames are also terminated by colons,
+and field splitting and pathname expansion are not performed.
.Ss Positional Parameters
A positional parameter is a parameter denoted by a number greater than zero.
The shell sets these initially to the values of its command line
built-in.
.It Va IFS
Input Field Separators.
-This is normally set to
+The default value is
.Aq space ,
.Aq tab ,
and
-.Aq newline .
+.Aq newline
+in that order.
+This default also applies if
+.Va IFS
+is unset, but not if it is set to the empty string.
See the
.Sx White Space Splitting
section for more details.
If a parameter expansion occurs inside double-quotes:
.Bl -enum
.It
-Pathname expansion is not performed on the results of the
-expansion.
-.It
Field splitting is not performed on the results of the
expansion, with the exception of the special parameter
.Va @ .
+.It
+Pathname expansion is not performed on the results of the
+expansion.
.El
.Pp
In addition, a parameter expansion can be modified by using one of the
.Pp
The result of the expression is substituted in decimal.
.Ss White Space Splitting (Field Splitting)
-After parameter expansion, command substitution, and
+In certain contexts,
+after parameter expansion, command substitution, and
arithmetic expansion the shell scans the results of
expansions and substitutions that did not occur in double-quotes for
field splitting and multiple fields can result.
.Pp
-The shell treats each character of the
+Characters in
+.Va IFS
+that are whitespace
+.Po
+.Aq space ,
+.Aq tab ,
+and
+.Aq newline
+.Pc
+are treated differently from other characters in
+.Va IFS .
+.Pp
+Whitespace in
+.Va IFS
+at the beginning or end of a word is discarded.
+.Pp
+Subsequently, a field is delimited by either
+.Bl -enum
+.It
+a non-whitespace character in
+.Va IFS
+with any whitespace in
+.Va IFS
+surrounding it, or
+.It
+one or more whitespace characters in
+.Va IFS .
+.El
+.Pp
+If a word ends with a non-whitespace character in
+.Va IFS ,
+there is no empty field after this character.
+.Pp
+If no field is delimited, the word is discarded.
+In particular, if a word consists solely of an unquoted substitution
+and the result of the substitution is null,
+it is removed by field splitting even if
.Va IFS
-variable as a delimiter and uses
-the delimiters to split the results of parameter expansion and command
-substitution into fields.
+is null.
.Ss Pathname Expansion (File Name Generation)
Unless the
.Fl f