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Top Forums Shell Programming and Scripting cannot properly employ "or" operator in an if statement (bash) Post 302444803 by agama on Thursday 12th of August 2010 10:50:27 PM
Old 08-12-2010
Your original if statement was nearly correct. There must be a complete expression on either side of the or:

Code:
if [[ $sername == *DIFF*FA* || $sername ==  *DTI*FA* ]]

Your second attempt isn't working because

Code:
[ expression ]

is very much different than
Code:
[[ expression ]]

The double bracket expression is interpreted by the shell and the right hand side is treated as a pattern (if not quoted). Single brackets are treated just like any any other command (remember that [ is a link to the test command). If wildcards (* and ?) are used inside of single brackets, they are expanded as file names in the current directory and NOT treated as patterns. The filename expansion is then passed to the test command.

In my opinion it is best to avoid using single brackets in if and while statements in Kshell and bash. Forking to the test command is very inefficient not to mention the enhancements to the expressions that Kshell and bash provide.
 

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test(1B)					     SunOS/BSD Compatibility Package Commands						  test(1B)

NAME
test - condition evaluation command SYNOPSIS
/usr/ucb/test expression expression DESCRIPTION
test evaluates the expression expression and, if its value is true, sets 0 (true) exit status; otherwise, a non-zero (false) exit status is set. test also sets a non-zero exit status if there are no arguments. When permissions are tested, the effective user ID of the process is used. All operators, flags, and brackets (brackets used as shown in the second SYNOPSIS line) must be separate arguments to the test command; normally these items are separated by spaces. USAGE
Primitives The following primitives are used to construct expression: -r filename True if filename exists and is readable. -w filename True if filename exists and is writable. -x filename True if filename exists and is executable. -f filename True if filename exists and is a regular file. Alternatively, if /usr/bin/sh users specify /usr/ucb before /usr/bin in their PATH environment variable, then test will return true if filename exists and is (not-a-directory). This is also the default for /usr/bin/csh users. -d filename True if filename exists and is a directory. -c filename True if filename exists and is a character special file. -b filename True if filename exists and is a block special file. -p filename True if filename exists and is a named pipe (fifo). -u filename True if filename exists and its set-user- ID bit is set. -g filename True if filename exists and its set-group- ID bit is set. -k filename True if filename exists and its sticky bit is set. -s filename True if filename exists and has a size greater than zero. -t[ fildes ] True if the open file whose file descriptor number is fildes (1 by default) is associated with a terminal device. -z s1 True if the length of string s1 is zero. -n s1 True if the length of the string s1 is non-zero. s1 = s2 True if strings s1 and s2 are identical. s1 != s2 True if strings s1 and s2 are not identical. s1 True if s1 is not the null string. n1 -eq n2 True if the integers n1 and n2 are algebraically equal. Any of the comparisons -ne, -gt, -ge, -lt, and -le may be used in place of -eq. Operators These primaries may be combined with the following operators: ! Unary negation operator. -a Binary and operator. -o Binary or operator (-a has higher precedence than -o). (expression) Parentheses for grouping. Notice also that parentheses are meaningful to the shell and, therefore, must be quoted. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWscpu | +-----------------------------+-----------------------------+ SEE ALSO
find(1), sh(1), attributes(5) NOTES
The not-a-directory alternative to the -f option is a transition aid for BSD applications and may not be supported in future releases. If you test a file you own (the -r , -w , or -x tests), but the permission tested does not have the owner bit set, a non-zero (false) exit status will be returned even though the file may have the group or other bit set for that permission. The correct exit status will be set if you are super-user. The = and != operators have a higher precedence than the -r through -n operators, and = and != always expect arguments; therefore, = and != cannot be used with the -r through -n operators. If more than one argument follows the -r through -n operators, only the first argument is examined; the others are ignored, unless a -a or a -o is the second argument. SunOS 5.11 1 Apr 1996 test(1B)
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