if.1 - nroff source : Read if(1) in pdf, ps, or txt form. IF(1) General Commands IF(1) NAME if - conditional command SYNOPSIS if expression [command [arg ...]] DESCRIPTION If evaluates expression, and if its value is true, returns a zero exit status or executes the specified command with the given arguments. Otherwise, a non-zero exit status is returned. The following primaries are used to construct expression: { command [arg ...] } The specified command is executed with the given arguments to obtain its exit status. A zero status is true, and a non- zero status is false. -d file True if file exists and is a directory. -e file True if file exists. -f file True if file exists and is a regular file. -h file True if file exists and is a symbolic link. -r file True if file exists and is readable. -s file True if file exists and has a size greater than zero bytes. -t fildes True if the file whose file descriptor number is fildes is open and associated with a terminal device. Fildes must be a decimal digit (0 - 9). -w file True if file exists and is writable. -x file True if file exists and is executable, or if file is a searchable directory. file1 -ef file2 True if file1 and file2 both exist and refer to the same file (same device, same inode). file1 -nt file2 True if file1 and file2 both exist and last data-modification time of file1 is newer than that of file2. file1 -ot file2 True if file1 and file2 both exist and last data-modification time of file1 is older than that of file2. s1 = s2 True if the strings s1 and s2 are equal. s1 != s2 True if the strings s1 and s2 are not equal. These primaries may also be combined with the following operators: ! expression unary negation operator expression1 -a expression2 binary and operator expression1 -o expression2 binary or operator ( expression ) parentheses for grouping -a has higher precedence than -o. Notice that all of the operators and flags are separate arguments to if. Notice also that parentheses are meaningful to the shell and must be escaped. EXIT STATUS The if command exits with one of the following values: 0 The expression was true (see below). 1 The expression was false or was not specified. 2 An error was detected. 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. 126 The specified command was found but could not be executed. 127 The specified command was not found. If the expression is true and if command is specified and executed, the exit status is that of the executed command. 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: 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. 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. SEE ALSO goto(1), osh(1), sh6(1), test(1) Osh home page: http://v6shell.org/ COMPATIBILITY The if command from Sixth Edition UNIX does not support the -d, -e, -f, -h, -s, -t, -x, -ef, -nt, and -ot operators. 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 test(1). HISTORY An if command appeared as /bin/if in Third Edition UNIX. LICENSE See either the LICENSE file which is distributed with osh or http://v6shell.org/license/ for full details. COPYRIGHT Copyright (c) 2004-2010 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. osh-20100430 April 30, 2010 IF(1)
