if.1

.\"
.\" Copyright (c) 2004-2011
.\"	Jeffrey Allen Neitzel <jan (at) v6shell (dot) org>.
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.\"	Derived from: Sixth Edition UNIX /usr/man/man1/if.1
.\"
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.\" modification, are permitted provided that the following conditions
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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.TH IF 1 "@OSH_DATE@" "@OSH_VERSION@" "General Commands"
.SH NAME
if \- conditional command
.SH SYNOPSIS
.B if
[\fIexpression\fR [\fIcommand\fR [\fIarg ...\fR]]]
.SH DESCRIPTION
.I If
evaluates the specified
.IR expression ,
and if its value is true,
returns a zero exit status or executes
the specified
.I command
with the given arguments.
Otherwise,
it returns a non-zero exit status.
When
.I expression
is not specified,
.I if
also returns a non-zero exit status.
.PP
The following primaries are used to construct
.IR expression :
.TP 10
\fB{\fR \fIcommand\fR [\fIarg ...\fR] \fB}\fR
The specified \fIcommand\fR is executed with the
given arguments to obtain its exit status.
A zero status is \fItrue\fR;
a non-zero status is \fIfalse\fR.
.TP
.BI \-d \ file
True if \fIfile\fR exists and is a directory.
.TP
.BI \-e \ file
True if \fIfile\fR exists.
.TP
.BI \-f \ file
True if \fIfile\fR exists and is a regular file.
.TP
.BI \-h \ file
True if \fIfile\fR exists and is a symbolic link.
.TP
.BI \-r \ file
True if \fIfile\fR exists and is readable.
.TP
.BI \-s \ file
True if \fIfile\fR exists and has a size greater than zero bytes.
.TP
.BI \-t \ fildes
True if the file whose file descriptor number is
.I fildes
is open and associated with a terminal device.
.I Fildes
must be a decimal digit (0 \- 9).
.TP
.BI \-w \ file
True if \fIfile\fR exists and is writable.
.TP
.BI \-x \ file
True if \fIfile\fR exists and is executable,
or if \fIfile\fR is a searchable directory.
.TP
.IB file1 \ \-ef \ file2
True if \fIfile1\fR and \fIfile2\fR both exist and refer
to the same file (same device, same inode).
.TP
.IB file1 \ \-nt \ file2
True if \fIfile1\fR and \fIfile2\fR both exist
and last data-modification time of \fIfile1\fR
is newer than that of \fIfile2\fR.
.TP
.IB file1 \ \-ot \ file2
True if \fIfile1\fR and \fIfile2\fR both exist
and last data-modification time of \fIfile1\fR
is older than that of \fIfile2\fR.
.TP
.IB s1 \ = \ s2
True if the strings
.I s1
and
.I s2
are equal.
.TP
.IB s1 \ != \ s2
True if the strings
.I s1
and
.I s2
are not equal.
.PP
These primaries may also be combined
with the following operators:
.TP 10
.BI ! \ expression
unary
.I negation
operator
.TP
.IB expression1 \ \-a \ expression2
binary
.I and
operator
.TP
.IB expression1 \ \-o \ expression2
binary
.I or
operator
.TP
.BI ( \ expression \ )
parentheses for grouping
.PP
.B \-a
has higher precedence than
.BR \-o .
Notice that all of the operators and flags
are separate arguments to
.IR if .
Notice also that parentheses are meaningful
to the shell and must be escaped.
.PP
In addition,
except for the
.B \-h
primary,
symbolic links are followed for all
other \fIfile\fR-related primaries.
.\" primaries that refer to filesystem objects.
.\" primaries that refer to files.
.SH "EXIT STATUS"
The
.I if
command exits with one of the following values:
.TP
0
The expression was true (see below).
.TP
1
The expression was false or was not specified.
.TP
2
An error was detected.
.TP
125
The specified command was found
but did not begin with the proper
magic number or a `#!shell' sequence,
and a valid shell was not specified by
EXECSHELL
with which to execute it.
.TP
126
The specified command was found
but could not be executed.
.TP
127
The specified command was not found.
.PP
If the expression is true and if
.I command
is specified and executed,
the exit status is that of the executed
.IR command .
.SH ENVIRONMENT
Notice that the concept of `user environment'
was not defined in Sixth Edition UNIX.
Thus,
use of the following environment variables
by this port of the conditional command is an enhancement:
.TP
.B EXECSHELL
If set to a non-empty string,
the value of this variable is taken as the
path name of the shell which is invoked to
execute the specified command when it does not
begin with the proper magic number
or a `#!shell' sequence.
.TP
.B PATH
If set to a non-empty string,
the value of this variable is taken as the
sequence of directories which is used to
search for the specified command.
Notice that the
conditional command from Sixth Edition UNIX
always used the equivalent of `.:/bin:/usr/bin',
not PATH.
.SH "SEE ALSO"
goto(1),
osh(1),
sh6(1),
test(1)
.PP
Osh home page:
http://v6shell.org/
.SH COMPATIBILITY
The
.I if
command from Sixth Edition UNIX
does not support the
.BR \-d ,
.BR \-e ,
.BR \-f ,
.BR \-h ,
.BR \-s ,
.BR \-t ,
.BR \-x ,
.BR \-ef ,
.BR \-nt ,
and
.B \-ot
operators.
.PP
In addition to supporting the above operators,
this port also differs from the original in that
the exit status returned varies according to whether
the expression is true or false,
as is the case with
.IR test (1).
.SH HISTORY
An
.I if
command
appeared as
.I /bin/if
in Third Edition UNIX.
.SH LICENSE
See either the LICENSE file which is distributed with
.I osh
or
http://v6shell.org/license/
for full details.
.SH COPYRIGHT
.nf
Copyright (c) 2004-2011
	Jeffrey Allen Neitzel.  All rights reserved.

Copyright (c) 2001-2002
	Caldera International Inc.  All rights reserved.

Copyright (c) 1985, 1989, 1991, 1993
	The Regents of the University of California.  All rights reserved.
.fi