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Diffstat (limited to 'bin/expr/expr.1')
| -rw-r--r-- | bin/expr/expr.1 | 113 |
1 files changed, 97 insertions, 16 deletions
diff --git a/bin/expr/expr.1 b/bin/expr/expr.1 index 9da5269..2c4fb792 100644 --- a/bin/expr/expr.1 +++ b/bin/expr/expr.1 @@ -30,7 +30,7 @@ .\" .\" $FreeBSD$ .\" -.Dd July 3, 1993 +.Dd March 22, 2002 .Dt EXPR 1 .Os .Sh NAME @@ -38,6 +38,7 @@ .Nd evaluate expression .Sh SYNOPSIS .Nm +.Op Fl \&- .Ar expression .Sh DESCRIPTION The @@ -46,12 +47,21 @@ utility evaluates .Ar expression and writes the result on standard output. .Pp -All operators are separate arguments to the +All operators and operands must be passed as separate arguments. +Several of the operators have special meaning to command interpreters +and must therefore be quoted appropriately. +.Pp +Arithmetic operations are performed using signed integer math, +in the largest integral type available in the C language. The .Nm -utility. -Characters special to the command interpreter must be escaped. +utility will detect arithmetic overflow and division by zero, and +returns with an exit status of 2 in those cases. If a numeric operand +is specified which is so large as to overflow conversion to an integer, +it is parsed as a string instead. All numeric operands are interpreted +in base 10. .Pp -Operators are listed below in order of increasing precedence. +Operators are listed below in order of increasing precedence; all +are left-associative. Operators with equal precedence are grouped within { } symbols. .Bl -tag -width indent .It Ar expr1 Li | Ar expr2 @@ -82,8 +92,9 @@ operator matches .Ar expr1 against .Ar expr2 , -which must be a regular expression. The regular expression is anchored -to the beginning of the string with an implicit +which must be a basic regular expression. +The regular expression is anchored +to the beginning of the string with an implicit .Dq ^ . .Pp If the match succeeds and the pattern contains at least one regular @@ -99,19 +110,89 @@ otherwise 0. .El .Pp Parentheses are used for grouping in the usual manner. +.Pp +This version of +.Nm +adheres to the +.Tn POSIX +Utility Syntax Guidelines, which require that a leading argument beginning +with a minus sign be considered an option to the program. +The standard +.Ql \&-- +syntax may be used to prevent this interpretation. +However, many historic implementations of +.Nm , +including the one in previous versions of +.Fx , +will not permit this syntax. +See the examples below for portable ways to guarantee the correct +interpretation. +.Pp +The +.Nm +utility makes no lexical distinction between arguments which may be +operators and arguments which may be operands. +An operand which is lexically identical to an operator will be considered a +syntax error. +See the examples below for a work-around. +.Pp +The syntax of the +.Nm +command in general is historic and inconvenient. +New applications are advised to use shell arithmetic rather than +.Nm . .Sh EXAMPLES .Bl -enum .It -The following example adds one to the variable a. -.Dl a=`expr $a + 1` +The following example (in +.Xr sh 1 +syntax) adds one to the variable +.Va a . +.Dl a=$(expr $a + 1) +.Li +This will fail if the value if +.Va a +is a negative number. +To protect negative values of +.Va a +from being interpreted as options to the +.Nm +command, one might rearrange the expression: +.Dl a=$(expr 1 + $a) +.Li +More generally, parenthesize possibly-negative values: +.Dl a=$(expr \e( $a \e) + 1) .It -The following example returns the filename portion of a pathname stored -in variable a. The // characters act to eliminate ambiguity with the -division operator. -.Dl expr "//$a" Li : '.*/\e(.*\e)' +The following example prints the filename portion of a pathname stored +in variable +.Va a . +Since +.Va a +might represent the path +.Pa / , +it is necessary to prevent it from being interpreted as the division operator. +The +.Li // +characters resolve this ambiguity. +.Dl expr \*q//$a\*q \&: '.*/\e(.*\e)' .It -The following example returns the number of characters in variable a. -.Dl expr $a Li : '.*' +The following examples output the number of characters in variable +.Va a . +Again, if +.Va a +might begin with a hyphen, it is necessary to prevent it from being +interpreted as an option to +.Nm . +If the +.Nm +command conforms to +.St -p1003.1-2001 , +this is simple: +.Dl expr -- \*q$a\*q \&: \*q.*\*q +.Li +For portability to older systems, however, a more complicated command +is required: +.Dl expr \e( \*qX$a\*q \&: \*q.*\*q \e) - 1 .El .Sh DIAGNOSTICS The @@ -132,4 +213,4 @@ the expression is invalid. The .Nm utility conforms to -.St -p1003.2 . +.St -p1003.1-2001 . |
