244 lines
6.7 KiB
Groff
244 lines
6.7 KiB
Groff
.TH EXPR 1
|
|
.SH NAME \" Copyright (C) 1989 by Kenneth Almquist.
|
|
expr, test, [ \- evaluate expressions
|
|
.SH SYNOPSIS
|
|
.B expr
|
|
.I expression
|
|
.br
|
|
.B test
|
|
.I expression
|
|
.br
|
|
.B [
|
|
.I expression
|
|
.B ]
|
|
.SH DESCRIPTION
|
|
.B Expr
|
|
evaluates the expression and prints the result.
|
|
.B Test
|
|
evaluates the expression without printing the result.
|
|
The ``[''
|
|
command is a synonym for
|
|
.BR test ;
|
|
when invoked under this name
|
|
the last argument to
|
|
.B expr
|
|
must be a ``]'', which is deleted and not considered part of the expression.
|
|
.PP
|
|
Three data types may occur in the
|
|
.IR expression :
|
|
string, integer, and boolean.
|
|
The rules for conversion are as follows:
|
|
.sp
|
|
.nr i 2
|
|
.ta \nii
|
|
.in +\nii
|
|
.ti -\nii
|
|
\fIstring\fR\->\fIinteger\fR Done via
|
|
.BR atoi (3).
|
|
.ti -\nii
|
|
\fIinteger\fR\->\fIstring\fR Convert to decimal representation.
|
|
.ti -\nii
|
|
\fIstring\fR\->\fIboolean\fR "" \-> false, everything else to true.
|
|
.ti -\nii
|
|
\fIboolean\fR\->\fIstring\fR false \-> "", true \-> "true".
|
|
.ti -\nii
|
|
\fIinteger\fR\->\fIboolean\fR 0 \-> false, everything else to true.
|
|
.ti -\nii
|
|
\fIboolean\fR\->\fIinteger\fR false \-> 0, true \-> 1.
|
|
.in -\nii
|
|
.PP
|
|
Any argument to
|
|
.B expr
|
|
which is not a legal operator is treated as a string operand of type
|
|
.BR string .
|
|
.PP
|
|
As a special case, if
|
|
.I expression
|
|
is omitted, the result is false.
|
|
.PP
|
|
We now list the operators. The syntax
|
|
.sp
|
|
.ti +8
|
|
\fIinteger\fB op \fIinteger\fR \-> \fIboolean\fB (3)\fR
|
|
.sp
|
|
means that \fBop\fR is a binary operator which takes operands of type
|
|
\fIinteger\fR and produces a result of type \fIboolean\fR.
|
|
The ``(3)'' means that the priority of \fBop\fR is 3.
|
|
Operands are automatically converted to the appropriate type. The type
|
|
\fIany\fR is used for operator that take operands of any type.
|
|
.nr p 1
|
|
.de b
|
|
.TP 0.5i
|
|
\fI\\$1\fB \\$2 \fI\\$3\fR \-> \\fI\\$4\\fR (\\np)
|
|
..
|
|
.de u
|
|
.TP 0.5i
|
|
\\$1 \fI\\$2\fR \-> \\fI\\$3\\fR (\\np)
|
|
..
|
|
.b any \-o any any
|
|
Returns the value of the left hand operand if the left hand operand
|
|
would yield
|
|
.B true
|
|
if converted to type
|
|
.BR boolean ,
|
|
and the value of the right hand operand otherwise.
|
|
The right hand operand is evaluated only if necessary.
|
|
``|'' is a synonym for ``\-o''.
|
|
.nr p \np+1
|
|
.b any -a any any
|
|
Returns the value of the left hand operand if the left hand operand
|
|
would yield
|
|
.B false
|
|
if converted to type
|
|
.BR boolean ,
|
|
and the value of the right hand operand otherwise.
|
|
The right hand operand is evaluated only if necessary.
|
|
``&'' is a synonym for ``\-a''.
|
|
.nr p \np+1
|
|
.u ! boolean boolean
|
|
Returns true if the operand is false, and false if the operand is true.
|
|
.nr p \np+1
|
|
.b string = string boolean
|
|
True if the two strings are equal.
|
|
.b string != string boolean
|
|
True if the two strings are not equal.
|
|
.b integer \-eq integer boolean
|
|
True if the two operands are equal.
|
|
.b integer \-ne integer boolean
|
|
True if the two operands are not equal.
|
|
.b integer \-gt integer boolean
|
|
True if the first operand is greater than the second one.
|
|
.b integer \-lt integer boolean
|
|
True if the first operand is less than the second one.
|
|
.b integer \-ge integer boolean
|
|
True if the first operand is greater than or equal to the second one.
|
|
.b integer \-le integer boolean
|
|
True if the first operand is less than or equal to the second one.
|
|
.nr p \np+1
|
|
.b integer + integer integer
|
|
Add two integers.
|
|
.b integer \- integer integer
|
|
Subtract two integers.
|
|
.nr p \np+1
|
|
.b integer * integer integer
|
|
Multiply two integers. ``*'' is special to the shell, so you generally
|
|
have to write this operator as ``\e*''.
|
|
.b integer / integer integer
|
|
Divide two integers.
|
|
.b integer % integer integer
|
|
Returns the remainder when the first operand is divided by the second one.
|
|
.nr p \np+1
|
|
.b string : string "integer or string"
|
|
The second operand is interpreted as a regular expression (as in the
|
|
System V
|
|
.B ed
|
|
program).
|
|
This operator attempts to match part (or all) of the first operand
|
|
with the regular expression. The match must start at the beginning of
|
|
the first operand.
|
|
If the regular expression contains \e( \e) pairs, then the result
|
|
of this operator is the string which is matched by the regular expression
|
|
between these pairs, or the null string if no match occurred. Otherwise,
|
|
the result is the number of characters matched by the regular expression,
|
|
or zero if no no match occurred.
|
|
.nr p \np+1
|
|
.u \-n string integer
|
|
Returns the number of characters in the string.
|
|
.u \-z string boolean
|
|
Returns true if the string contains zero characters.
|
|
.u \-t integer boolean
|
|
Returns true if the specified file descriptor is associated with a tty.
|
|
.PP
|
|
The remaining operators all deal with files. Except as noted, they return
|
|
false if the
|
|
specified file does not exist. The ones dealing with permission use
|
|
the effective user and group ids of the shell.
|
|
.u \-r string boolean
|
|
True if you have read permission on the file.
|
|
.u \-w string boolean
|
|
True if you have write permission on the file.
|
|
.u \-x string boolean
|
|
True if you have execute permission on the file.
|
|
.u \-f string boolean
|
|
True if the file is a regular file.
|
|
.u \-d string boolean
|
|
True if the file is a directory.
|
|
.u \-c string boolean
|
|
True if the file is a character special file.
|
|
.u \-b string boolean
|
|
True if the file is a block special file.
|
|
.u \-p string boolean
|
|
True if the file is a named pipe (i.e. a fifo).
|
|
.u \-u string boolean
|
|
True if the file is setuid.
|
|
.u \-g string boolean
|
|
True if the file is setgid.
|
|
.u \-k string boolean
|
|
True if the file has the sticky bit set.
|
|
.u \-s string "integer or boolean"
|
|
Returns the size of the file, or 0 if the file does not exist.
|
|
.u \-h string boolean
|
|
True if the file is a symlink. This is the only file test operator that
|
|
does not follow symlinks, all others do. So ``\-d'' and ``\-h''
|
|
are both true on a symlink pointing to a directory.
|
|
``\-L'' is a synonym for ``\-h''.
|
|
.SH "EXIT CODE"
|
|
0 if the result of
|
|
.I expression
|
|
would be
|
|
.B true
|
|
if the result were converted to
|
|
.BR boolean .
|
|
.br
|
|
1 if the result of
|
|
.I expression
|
|
would be
|
|
.B false
|
|
if the result were converted to
|
|
.BR boolean .
|
|
.br
|
|
2 if
|
|
.I expression
|
|
is syntactically incorrect.
|
|
.SH EXAMPLES
|
|
.TP 0.5i
|
|
filesize=`expr \-s file`
|
|
Sets the shell variable
|
|
.I filesize
|
|
to the size of
|
|
.IR file .
|
|
.TP 0.5i
|
|
if [ \-s file ]; then command; fi
|
|
Execute
|
|
.I command
|
|
if
|
|
.I file
|
|
exists and is not empty.
|
|
.TP 0.5i
|
|
x=`expr "$x" : '.\\{4\\}\\(.\\{0,3\\}\\)'`
|
|
Sets
|
|
.I x
|
|
to the substring of
|
|
.I x
|
|
beginning after the fourth character of
|
|
.I x
|
|
and continuing for three characters or until the end of the string,
|
|
whichever comes first.
|
|
.TP 0.5i
|
|
x=`expr X"$x" : X'.\\{4\\}\\(.\\{0,3\\}\\)'`
|
|
This example is the same as the previous one, but it uses a leading
|
|
``X'' to make things work when the value of
|
|
.I x
|
|
looks like an operator.
|
|
.SH BUGS
|
|
The relational operators of the System V
|
|
.B expr
|
|
command are not implemented.
|
|
.PP
|
|
Certain features of this version of
|
|
.B expr
|
|
are not present in System V, so care should be used when writing
|
|
portable code.
|
|
.SH COPYRIGHT
|
|
Kenneth Almquist.
|