expr/expr.1

   1 .\"     $NetBSD: expr.1,v 1.10 1997/10/20 08:51:56 enami Exp $
   2 .\"
   3 .\" Written by J.T. Conklin <jtc@netbsd.org>.
   4 .\" Public domain.
   5 .\"
   6 .Dd July 3, 1993
   7 .Dt EXPR 1
   8 .Os
   9 .Sh NAME
  10 .Nm expr
  11 .Nd evaluate expression
  12 .Sh SYNOPSIS
  13 .Nm
  14 .Ar expression
  15 .Sh DESCRIPTION
  16 The
  17 .Nm
  18 utility evaluates
  19 .Ar expression
  20 and writes the result on standard output.
  21 .Pp
  22 All operators are separate arguments to the
  23 .Nm
  24 utility.
  25 Characters special to the command interpreter must be escaped.
  26 .Pp
  27 Operators are listed below in order of increasing precedence.
  28 Operators with equal precedence are grouped within { } symbols.
  29 .Bl -tag -width indent
  30 .It Ar expr1 Li | Ar expr2
  31 Returns the evaluation of
  32 .Ar expr1
  33 if it is neither an empty string nor zero;
  34 otherwise, returns the evaluation of
  35 .Ar expr2 .
  36 .It Ar expr1 Li & Ar expr2
  37 Returns the evaluation of
  38 .Ar expr1
  39 if neither expression evaluates to an empty string or zero;
  40 otherwise, returns zero.
  41 .It Ar expr1 Li "{=, >, >=, <, <=, !=}" Ar expr2
  42 Returns the results of integer comparison if both arguments are integers;
  43 otherwise, returns the results of string comparison using the locale-specific
  44 collation sequence.
  45 The result of each comparison is 1 if the specified relation is true,
  46 or 0 if the relation is false.
  47 .It Ar expr1 Li "{+, -}" Ar expr2
  48 Returns the results of addition or subtraction of integer-valued arguments.
  49 .It Ar expr1 Li "{*, /, %}" Ar expr2
  50 Returns the results of multiplication, integer division, or remainder of integer-valued arguments.
  51 .It Ar expr1 Li : Ar expr2
  52 The
  53 .Dq \&:
  54 operator matches
  55 .Ar expr1
  56 against
  57 .Ar expr2 ,
  58 which must be a regular expression.  The regular expression is anchored
  59 to the beginning of  the string with an implicit
  60 .Dq ^ .
  61 .Nm
  62 expects "basic" regular expressions, see
  63 .Xr re_format 7
  64 for more information on regular expressions.
  65 .Pp
  66 If the match succeeds and the pattern contains at least one regular
  67 expression subexpression
  68 .Dq "\e(...\e)" ,
  69 the string corresponding to
  70 .Dq "\e1"
  71 is returned;
  72 otherwise the matching operator returns the number of characters matched.
  73 If the match fails and the pattern contains a regular expression subexpression
  74 the null string is returned;
  75 otherwise 0.
  76 .El
  77 .Pp
  78 Parentheses are used for grouping in the usual manner.
  79 .Sh EXAMPLES
  80 .Bl -enum
  81 .It
  82 The following example adds one to the variable a.
  83 .Dl a=`expr $a + 1`
  84 .It
  85 The following example returns the filename portion of a pathname stored
  86 in variable a.  The // characters act to eliminate ambiguity with the
  87 division operator.
  88 .Dl expr "//$a" Li : '.*/\e(.*\e)'
  89 .It
  90 The following example returns the number of characters in variable a.
  91 .Dl expr $a Li : '.*'
  92 .El
  93 .Sh DIAGNOSTICS
  94 The
  95 .Nm
  96 utility exits with one of the following values:
  97 .Bl -tag -width Ds -compact
  98 .It 0
  99 the expression is neither an empty string nor 0.
 100 .It 1
 101 the expression is an empty string or 0.
 102 .It 2
 103 the expression is invalid.
 104 .El
 105 .Sh STANDARDS
 106 The
 107 .Nm
 108 utility conforms to
 109 .St -p1003.2 .