The bash environment variable PROMPT_COMMAND contains a regular bash command that is executed just before the command prompt is displayed. For example: $ export PROMPT_COMMAND=a bash: a: command not ... The command a is not valid so you get the error message every time you hit enter. Echo something before $PS1 : $ export PROMPT_COMMAND='echo -n Hi!' Hi!$ ... PROMPT_COMMAND is regularly used to change the xterm window title. You may find this in /etc/bashrc : case $TERM in xterm*) if [ -...

PHP global variables are defined outside of functions and classes. They are visible both in the current file and in any included/required files. Also, any global variables defined in required/included files are visible in the current file. But they are not visible in any functions or classes, unless specifically declared global . Test: Create file test.php : <?php ini_set('display_errors', 'stderr'); i... Create file test.inc : <?php echo '[', __FILE__, '] $a . $b = ', $... Run the PHP script in command line: php test.php 2>C:\tmp\stderr.out The result is: [C:\work\test.inc] $a . $b = ab [C:\work\test.p... stderr messages: PHP Notice: Undefined variable: b in C:\work\scra...

Check the __name__ variable to see if the Python module was invoked from the command line. The line prints when the Python script is called from the command line, but doesn't print when it is imported by another Python module with import MyModule . if __name__ == '__main__': print 'Invoked f...

The Unix shell passes these parameters to the shell script: Variable Meaning $* A single string representing all command line arguments separated by $IFS (internal field separator, usually a space) $@ A sequence of strings representing the command line arguments. $1,$2...$n $1 is the first argument, $2 is the second argument, and so on... $0 The name of the script itself. $# The number of arguments. Example shell script ( sharg.sh ): #!/bin/sh echo $# arguments passed to $0: $@ ... Output for ./sharg.sh "a b c d" : 1 arguments passed to ./sharg.sh: a b c d here ... Output for ./sharg.sh a "b c" d : 3 arguments passed to ./sharg.sh: a b c d here ...

If Command Extensions are enabled (which is enabled by default), then there are several dynamic environment variables that can be expanded but which don't show up in the list of variables displayed by SET . These variable values are computed dynamically each time the value of the variable is expanded (but see example below). If the user explicitly defines a variable with one of these names, then that definition will override the dynamic one described below: %CD% - expands to the current directory string. %DATE% - expands to current date using same format as DATE command. %TIME% - expands to current time using same format as TIME command. %RANDOM% - expands to a random decimal number between 0 and 32767. %ERRORLEVEL% - expands to the...

Use the pg_ctl command to start/stop/restart the PostgreSQL server: $ bin/pg_ctl -D /usr/local/pgsql/data -l logs/post... Environment variable PGDATA can be set in lieu of the -D switch.

Compile mod_proxy_html from source code. Prerequisite: Apache httpd installed on system with header files. Command: # /usr/local/apache2/bin/apxs -i -c -I/usr/local/i... Output: /usr/local/apache2/build/libtool --silent --mode=c...

It's quite easy for Perl to open a pipe and read from it: $file = "nospace.txt"; open(IN, "cat $file |") ... But the code breaks when the file name contains a space: # This does not work! $file = "yes space.txt"; ... On Windows, these don't work either: # This does not work! $file = "yes space.txt"; ... You need to use a technique called Safe Pipe Opens : $file = "yes space.txt"; $prog = "cat"; ...

Variable Meaning $_ The default or implicit variable. @_ Within a subroutine the array @_ contains the parameters passed to that subroutine. $a, $b Special package variables when using sort() $<digit> Contains the subpattern from the corresponding set of capturing parentheses from the last pattern match, not counting patterns matched in nested blocks that have been exited already. $. Current line number for the last filehandle accessed. $/ The input record separator, newline by default. $| If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel. Default is 0 (regardless of whether the channel is really buffered by the system or not; $| tells you only whether you've asked Perl explicitly to flush after...

Variable Description SET AUTO [COMMIT] {ON | OFF | IMM [EDIATE] | n} Controls when Oracle Database commits pending changes to the database. SET CMDS [EP] {; | c | ON | OFF} Sets the non-alphanumeric character used to separate multiple SQL*Plus commands entered on one line to c. SET CON [CAT] {. | c | ON | OFF} Sets the character you can use to terminate a substitution variable reference if you wish to immediately follow the variable with a character that SQL*Plus would otherwise interpret as a part of the substitution variable name. SET ECHO {ON | OFF} Controls whether the START (@) command lists each command in a script as the command is executed. SET EDITF [ILE] file_name[.ext] Sets the default filename...