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Created by magnum on October 22, 2012 19:48:03    Last update: October 22, 2012 19:48:03
execl takes the full path name of the command and variable length of arguments terminated by NULL: execl("/bin/ls", "/bin/ls", "-r", "-t", "-l", NULL... where the second argument is argv[0] , but can be any string! execlp will try to find the command from $PATH , so full path to command is not needed: execl("ls", "ls", "-r", "-t", "-l", NULL); execv is the equivalent of execl , except that the arguments are passed in as a NULL terminated array: char *args[] = {"/bin/ls", "-r", "-t", "-l", NULL ... execvp is the equivalent of execvl , excep that the arguments are passed in as a NULL terminated array: char *args[] = {"ls", "-r", "-t", "-l", NULL }; ...
Created by Dr. Xi on February 28, 2011 12:29:19    Last update: February 28, 2011 12:30:40
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 ( ): #!/bin/sh echo $# arguments passed to $0: $@ ... Output for ./ "a b c d" : 1 arguments passed to ./ a b c d here ... Output for ./ a "b c" d : 3 arguments passed to ./ a b c d here ...
Created by Dr. Xi on December 05, 2009 20:12:16    Last update: December 05, 2009 20:46:45
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"; ...
Created by Dr. Xi on December 04, 2009 04:33:05    Last update: December 04, 2009 04:33:05
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...
Created by Dr. Xi on September 29, 2008 23:03:40    Last update: September 29, 2008 23:04:08
Variables set automatically by shell: Variable Description $# Number of command-line arguments. $- Options currently in effect (arguments supplied to sh or to set). $? Exit value of last executed command. $$ Process number of current process. $! Process number of last background command. $0 First word; that is, command name. $n Individual arguments on command line (positional parameters). The Bourne shell allows only nine parameters to be referenced directly (n = 1-9); the Korn shell allows n to be greater than 9 if specified as ${n}. $* All arguments on command line ("$1 $2..."). $@ All arguments on command line, individually quoted ("$1" "$2" ...). Variables set automatically by Korn shell: Variable Description ERRNO Error number of last system call that failed. LINENO Current...
Created by Dr. Xi on September 23, 2008 20:43:58    Last update: September 23, 2008 20:43:58
Variable Description $0 The name of the ruby script file $* The command line arguments $$ Ruby interpreter's process ID $? Exit status of last executed child process $_ String last read by gets $. Line number last read by interpreter $! Last error message $@ Location of error $& String last matched by regexp $~ The last regexp match, as an array of subexpressions $n the nth subexpression in the last match (same as $~ ) $= Sase-insensitivity flag $/ Input record separator $\ Output record separator
Created by Dr. Xi on September 17, 2008 03:28:04    Last update: September 17, 2008 03:29:05
Starting with JDK1.5, Java allowed variable arguments (varargs) to methods. You use three dots after the final parameter type to indicate that variable number of arguments may be passed. Varargs can only be used in the final argument position. For example: static int sum (int ... numbers) { int total... Some examples from the Java API: java.text.MessageFormat: public static String format(String pattern, Object... java.lang.String: public static String format(String format, Object.... java.lang.ProcessBuilder: public ProcessBuilder(String... command)
Created by Dr. Xi on April 26, 2007 03:17:14    Last update: May 05, 2007 19:50:26
To loop through an envionment variable: @echo off set a=1 2 3 for %%i in (%a%) d... To loop through the command line arguments: @echo off for %%i in (%*) do echo %%i