if then else; no variable match but statement executes anyway. Post: 302707365

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Top Forums Shell Programming and Scripting if then else; no variable match but statement executes anyway. Post 302707365 by Don Cragun on Friday 28th of September 2012 11:53:47 AM

09-28-2012

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The first if command in your example does exactly what you want when I try it. (I use ksh; you haven't said what shell you're using.) In other words, it does not print 2012 because "12-31-12" is not "09-28-12".) It should work with any shell that supports the basic tenets of the shell command language defined by the the original Bourne shell. (This includes at least bash, ksh, and sh.)

The test statements in the rest of your if commands all evaluate to true because the strings "09-28-12==12-31-12" and "09-28-12=12-31-12" are not empty strings. In these cases == and = are just parts of a string; they are not comparison operators.

Assuming you are using bash, ksh, sh or a similar shell (NOT csh nor tcsh), you should get what you seem to want if you change: "$date"=="$date1" to "$date" == "$date1", $date==$date1 to $date == $date1, and $date=$date1 to $date = $date1, respectively.

You may note that the standards specify = as the operator to compare strings for equality, but I don't know of any POSIX-conforming shell that doesn't also recognize == (and most shell maintainers prefer == and consider = obsolete).

Don Cragun

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LEARN ABOUT OSF1

true

true(1) 						      General Commands Manual							   true(1)

NAME

       true, false - Returns a standard exit value

SYNOPSIS

       true

       false

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       true:  XCU5.0

       false:  XCU5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

DESCRIPTION

       The true command returns a 0 (zero) exit value. The false command returns a nonzero exit value. These commands are usually used in input to
       shell commands.

NOTES

       The special built-in utility : (colon) is sometimes more efficient than the true command.

EXIT STATUS

       [Tru64 UNIX]  The nonzero value returned by the false command may vary from system to system.

EXAMPLES

       To construct a loop in a shell procedure, enter: while true do	   date      sleep 60 done

       This procedure displays the date and time once a minute.  To stop it, press the Interrupt key sequence.

SEE ALSO

       Commands:  csh(1), ksh(1), Bourne Shell sh(1b), POSIX shell sh(1p)

       Standards:  standards(5)

																	   true(1)

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