PWB1/usr/man/man1/if.1

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.th IF I 5/31/77
.sh NAME
if \*-  conditional command
.sh SYNOPSIS
.bd if
expr command [ arg ... ]
.s3
.bd if
expr
.bd then
.br
	command(s)
.br
	...
.br
[
.bd else
[ command ]
.br
	... ]
.br
.bd endif
.s3
.bd test
expr
.sh DESCRIPTION
.it If
evaluates the expression
.it expr.
In the first form above, if
.it expr
is true, the given
.it command
is executed with the given arguments.
The command may be another
.it if.
.s3
In the second form, if
.it expr
is true, the commands
between the
.it then
and the next unmatched
.it else
or
.it endif
are  executed.
If
.it expr
is false, the commands after
.it then
are skipped, and the commands after the optional
.it else
are executed.
Zero or one commands may be written on the same line as the
.it else.
In particular,
.it if
may be used this way.
The pseudo commands
.it else
and
.it endif
(whichever occurs first)
must not be hidden behind semicolons or other commands.
This form may be nested: every
.it then
needs a matching
.it endif.
.s3
.it Test
is an entry to
.it if
that evaluates the expression and returns exit code 0 if it is true,
and code 1 if it is false or in error.
.s3
The following primitives are used to construct
the
.it expr:
.s3
.lp +13 13
\fB\*-r\fR\ file	true if the file exists and is readable.
.s3
.lp +13 13
\fB\*-w\ \fRfile	true if the file exists and is writable.
.s3
.lp +13 13
\fB\*-s\fR\ file	true if the file exists and has a size greater than zero.
.s3
.lp +13 13
\fB\*-f\fR\ file	true if the file exists and is an ordinary file.
.s3
.lp +13 13
\fB\*-d\fR\ file	true if the file exists and is a directory.
.s3
.lp +13 13
\fB\*-z\fR\ s1	true if the length of string
.it s1
is zero.
.s3
.lp +13 13
\fB\*-n\fR\ s1	true if the length of string
.it s1
is nonzero.
.s3
.lp +13 13
s1\ \fB=\ \fRs2	true
if the strings
.it s1
and
.it s2
are equal.
.s3
.lp +13 13
s1\ \fB!=\ \fRs2	true
if the strings
.it s1
and
.it s2
are not equal.
.s3
.if n .ne7
.lp +13 13
n1 \fB\*-eq\fR n2
.lp +13 13
n1 \fB\*-ne\fR n2
.lp +13 13
n1 \fB\*-gt\fR n2
.lp +13 13
n1 \fB\*-ge\fR n2
.lp +13 13
n1 \fB\*-lt\fR n2
.lp +13 13
n1 \fB\*-le\fR n2	true
if the stated algebraic
relationship exists.
The arguments
.it n1
and
.it n2
must be integers.
.s3
.lp +13 13
\fB{ \fRcommand \fB}\fR	The bracketed command is
executed to obtain the
exit status.
Status zero is considered
.it true.
The command must
.bd not
be another
.it if.
.s3
.i0
These primaries may be combined with the
following operators:
.s3
.lp +13 13
\fB!\fR	unary negation operator
.s3
.lp +13 13
\fB\*-a\fR	binary
.it and
operator
.s3
.lp +13 13
\fB\*-o\fR	binary
.it or
operator
.s3
.lp +13 13
\fB(\ \fRexpr\fB\ )\fR	parentheses for grouping.
.s3
.i0
.bd \*-a
has higher precedence than
.bd \*-o.
Notice that all the operators and flags are separate
arguments to
.it if
and hence must be surrounded by spaces.
Notice also that parentheses are meaningful
to the Shell and must be escaped.
.s3
.sh "EXIT CODES"
0 \*- true expression, no error.
.br
1 \*- false condition or error.
.sh "SEE ALSO"
exit(I), goto(I), sh(I), switch(I), while(I), exit(II)
.br
.sh DIAGNOSTICS
if:missing endif
.br
if:syntax error:
value
.br
if:non-numeric arg:
value
.br
if:no command:
name
.br
else:missing endif
.s3
.it Test
may issue any of the
.it if
messages above, except the first.
.sh BUGS
In general,
.it if,
.it else,
.it endif,
and
.it test
must not be hidden behind semicolons on a command line.
Many of the effects are obtained by
searching the input file and adjusting the read pointer appropriately.
Thus, including any of these commands in a part of the file intended to be read
by a command other than the shell may cause strange results
if they are encountered while searching.
.br
These commands ignore redirection or piping of their standard
input or output.
Commands executed by
.it if
or
.it test
may be affected by redirections,
but this practice is undesirable and should be avoided.