An argv vector normally ends in a null pointer? Usually, strtok should be tested to ensure there is a return (consider a for ( strtok ptr, ptr, strtok( NULL ) loop for neatness) (strtok is a good core dump generator if not handled very carefully)?
execvp does examine path, so I guess you are assigned writing execvp from execv.
I like to invest in white space to set off every loop, if, switch with new lines and indentation. I am not enjoying reading the code, so no a+ right off. You deserve structural indentation and spacing! You might always use {} with if/while/for, so you can easily add in debugging commands or additional function points.
Also, never use gets(); it is unsafe, use fgets( ..., stdin ), getchar() or read( 0, ... ).
Now, am in a very tight situation here. I really dont expect anyone to understand but please, try your best.
am trying to right a program that goes back to the previous entry to correct a mistake.
heres what am trying to do. i write a program like this
Name : James Holgston... (1 Reply)
Hellow every body
I am trying to write a very simple script in an executable file as following
if ($?PWD) then
echo "OK"
else
echo "No"
endif
but I am getting error during execution in c shell as
synthax error at line 4 , unexpected end of file
Please advise (2 Replies)
I am programming the following simple shell program. It works for the most part, things like 'ls' and 'ps' work just fine. However when I add options, (example, ls -l) it does not execute the command. Also, I've been trying to add an "exit" command, so that I don't have to use the iterrupt; but... (3 Replies)
How to write a shell script which takes 3 strings as positional parameters,first and second are file names and third is a directory.if the two files exist in `pwd` and they contain a specific pattern and their size is greater than 32 bytes,moves these files into directory? (1 Reply)
in the beginners book i have it gives an exercise to try. saying to make a script that examines the time. it should keep examining every second or so and say some sort of message. Can anyone help me get going.
Thanks (3 Replies)
I want to print the value of variables a1, a2, a3 in for loop in the following program:
a1=this
a2=is
a3=printed
for((i=1;i<4;i++))
do
var=a$i
#w=`echo $var`
e=${var}
echo $e
done
But actually I get a1,a2,a3 as the output not the "this is printed"
So the main question is if I... (3 Replies)
Iam having file 1 as
wc -l file1 is 8
QWEERTYUU|7927836357398398398913 yuyuyu uyiuyuyuyuy yuiyuiyuyuyy
FDHGFSHAJK|1476887897877777777771 iopwiiwpoi e
.
.
.
.
I Need to read the abouve line in file1
so iam using the command as
tail -n 8... (8 Replies)
Hi all,
I am trying to get a file from an ftp server and i have the list of files which needs to be get from the ftp server.
grep unix_prg*.* log.txt > log1.txt
log1.txt (which has the list of files)
06-29-09 00:00AM 3550258 unix_prg090629
06-28-09 07:00PM ... (7 Replies)
1. I've have to write a shell program that accepts Ctrl+T (in linux os in c language) and should print out the current time and date to the screen. I've written the following code but i've to type ^T individual rather than pressing ctrl+T(^T) to get the output. :
2. How do i make the shell... (2 Replies)
Discussion started by: zorro_phu
2 Replies
LEARN ABOUT BSD
execl
EXECL(3) Library Functions Manual EXECL(3)NAME
execl, execv, execle, execlp, execvp, exec, execve, exect, environ - execute a file
SYNOPSIS
execl(name, arg0, arg1, ..., argn, 0)
char *name, *arg0, *arg1, ..., *argn;
execv(name, argv)
char *name, *argv[];
execle(name, arg0, arg1, ..., argn, 0, envp)
char *name, *arg0, *arg1, ..., *argn, *envp[];
exect(name, argv, envp)
char *name, *argv[], *envp[];
extern char **environ;
DESCRIPTION
These routines provide various interfaces to the execve system call. Refer to execve(2) for a description of their properties; only brief
descriptions are provided here.
Exec in all its forms overlays the calling process with the named file, then transfers to the entry point of the core image of the file.
There can be no return from a successful exec; the calling core image is lost.
The name argument is a pointer to the name of the file to be executed. The pointers arg[0], arg[1] ... address null-terminated strings.
Conventionally arg[0] is the name of the file.
Two interfaces are available. execl is useful when a known file with known arguments is being called; the arguments to execl are the char-
acter strings constituting the file and the arguments; the first argument is conventionally the same as the file name (or its last compo-
nent). A 0 argument must end the argument list.
The execv version is useful when the number of arguments is unknown in advance; the arguments to execv are the name of the file to be exe-
cuted and a vector of strings containing the arguments. The last argument string must be followed by a 0 pointer.
The exect version is used when the executed file is to be manipulated with ptrace(2). The program is forced to single step a single
instruction giving the parent an opportunity to manipulate its state. On the VAX-11 this is done by setting the trace bit in the process
status longword. Exect is not available on the PDP-11.
When a C program is executed, it is called as follows:
main(argc, argv, envp)
int argc;
char **argv, **envp;
where argc is the argument count and argv is an array of character pointers to the arguments themselves. As indicated, argc is convention-
ally at least one and the first member of the array points to a string containing the name of the file.
Argv is directly usable in another execv because argv[argc] is 0.
Envp is a pointer to an array of strings that constitute the environment of the process. Each string consists of a name, an "=", and a
null-terminated value. The array of pointers is terminated by a null pointer. The shell sh(1) passes an environment entry for each global
shell variable defined when the program is called. See environ(7) for some conventionally used names. The C run-time start-off routine
places a copy of envp in the global cell environ, which is used by execv and execl to pass the environment to any subprograms executed by
the current program.
Execlp and execvp are called with the same arguments as execl and execv, but duplicate the shell's actions in searching for an executable
file in a list of directories. The directory list is obtained from the environment.
FILES
/bin/sh shell, invoked if command file found by execlp or execvp
SEE ALSO execve(2), fork(2), environ(7), csh(1)DIAGNOSTICS
If the file cannot be found, if it is not executable, if it does not start with a valid magic number (see a.out(5)), if maximum memory is
exceeded, or if the arguments require too much space, a return constitutes the diagnostic; the return value is -1. Even for the super-
user, at least one of the execute-permission bits must be set for a file to be executed.
BUGS
If execvp is called to execute a file that turns out to be a shell command file, and if it is impossible to execute the shell, the values
of argv[0] and argv[-1] will be modified before return.
4.2 Berkeley Distribution August 4, 1987 EXECL(3)