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Top Forums Shell Programming and Scripting Why I get bad bad substitution when using eval? Post 302548697 by michaelrozar17 on Friday 19th of August 2011 05:18:34 AM
Old 08-19-2011
Quote:
Originally Posted by 915086731
Code:
[river@localhost ate]$ eval echo  \${map$i[1]}
0000
[river@localhost ate]$ a=`eval echo \\${map$i[2]}`
[river@localhost ate]$ echo $a                                       ??not "0000"??
0 # <-- thats because we are calling here subscript 2 not 1

The following result is right!
Code:
[river@localhost ate]$ a=$(eval echo \${map$i[1]})
[river@localhost ate]$ echo $a
0000
[river@localhost ate]$

Thanks!
I feel very puzzled, why I must need add '\' more, or add $(). Can you tell me ?
Back-ticks ( a.k.a. grave accents) is considered archaic nowadays. The newer enhanced command substitution $(commands) is recommended instead of `commands`
 

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PHP_UNAME(3)								 1							      PHP_UNAME(3)

php_uname - Returns information about the operating system PHP is running on

SYNOPSIS
string php_uname ([string $mode = "a"]) DESCRIPTION
php_uname(3) returns a description of the operating system PHP is running on. This is the same string you see at the very top of the phpinfo(3) output. For the name of just the operating system, consider using the PHP_OS constant, but keep in mind this constant will con- tain the operating system PHP was built on. On some older UNIX platforms, it may not be able to determine the current OS information in which case it will revert to displaying the OS PHP was built on. This will only happen if your uname() library call either doesn't exist or doesn't work. PARAMETERS
o $mode -$mode is a single character that defines what information is returned: o 'a': This is the default. Contains all modes in the sequence "s n r v m". o 's': Operating system name. eg. FreeBSD. o 'n': Host name. eg. localhost.example.com. o 'r': Release name. eg. 5.1.2-RELEASE. o 'v': Version information. Varies a lot between operating systems. o 'm': Machine type. eg. i386. RETURN VALUES
Returns the description, as a string. EXAMPLES
Example #1 Some php_uname(3) examples <?php echo php_uname(); echo PHP_OS; /* Some possible outputs: Linux localhost 2.4.21-0.13mdk #1 Fri Mar 14 15:08:06 EST 2003 i686 Linux FreeBSD localhost 3.2-RELEASE #15: Mon Dec 17 08:46:02 GMT 2001 FreeBSD Windows NT XN1 5.1 build 2600 WINNT */ if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') { echo 'This is a server using Windows!'; } else { echo 'This is a server not using Windows!'; } ?> There are also some related Predefined PHP constants that may come in handy, for example: Example #2 A few OS related constant examples <?php // *nix echo DIRECTORY_SEPARATOR; // / echo PHP_SHLIB_SUFFIX; // so echo PATH_SEPARATOR; // : // Win* echo DIRECTORY_SEPARATOR; // echo PHP_SHLIB_SUFFIX; // dll echo PATH_SEPARATOR; // ; ?> SEE ALSO
phpversion(3), php_sapi_name(3), phpinfo(3). PHP Documentation Group PHP_UNAME(3)
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