S2argv-execs: something was missing in libc - Cronologia

Renzo: /* s2argv */

2015-03-07T14:57:42Z

s2argv

Renzo il 14:20, 27 mag 2014

2014-05-27T14:20:33Z

Renzo: /* execs and siblings */

2014-05-27T14:17:05Z

execs and siblings

Renzo: /* execs and siblings */

2014-05-27T14:15:14Z

execs and siblings

Renzo: /* execs and siblings */

2014-05-27T14:15:02Z

execs and siblings

Renzo: /* s2argv */

2014-05-27T14:14:42Z

s2argv

Renzo: /* execs and siblings */

2014-05-27T14:14:17Z

execs and siblings

Renzo: Creata pagina con 'Posix standard provides a number of functions to execute a file. It is the ''exec'' family. Some of them can take a variable number of args, others use an array of strings. T...'

2014-05-27T14:12:59Z

Creata pagina con 'Posix standard provides a number of functions to execute a file. It is the ''exec'' family. Some of them can take a variable number of args, others use an array of strings. T...'

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Posix standard provides a number of functions to execute a file. It is the ''exec'' family.

Some of them can take a variable number of args, others use an array of strings. The formers have a name having an 'l' in the suffix, the latters a 'v'.

But what do you do if you have a string including all the arguments separated by spaces.
This is the case, for instance, when the command has been provided by the user or read from a file.

It happened to me dozens of times.

There are two naive solutions. ''strtok'' and ''system''.
''strtok'' can be usen to tokenize the string, ''system'' delegates the problem to a shell.
Both solutions are unsitisfactory to me.
''system'' is unsafe (it is stated also on its man page!). ''strtok'' use spaces to split the string into pieces, modify the original string, do not support quotation or escape characters, It is also very annoying to use ''strtok'' to parse the arguments for an ''exec''.

I needed a clean solution to parse the arguments from a string.

So I decided to write the libs2argv library. (200 lines of C source).

It is not a historical achievement in the story of computing, but it is something that was missing and I felt the need for.

The code has been released on [https://github.com/rd235/s2argv-execs GitHub] under LGPL2.1+.

The API of the library is clean and straightforward.

There are two possible use cases.

==s2argv==
convert the string in a dynamically allocated argv using s2argv (string to argv):
char **s2argv(const char *args, int *pargc);

The return value is a valid argv, if ''pargc'' is non-NULL, the number of args, i.e. the argc, is stored in the integer field pointed to by ''pargc''. ''s2argv'' uses dynamic allocation and does not modify its input parameter ''args''.

''s2argv'' tokenize the arguments using spaces (blanks, tabs or newlines) but it also supports simple and double quotation
to specify arguments including spaces, and the escape char \\.

Usually an argv is used as an argument to an ''execv''. If the ''execv'' function succeeds, it is useless to deallocate the
argv, all the memory of the calling program has been deallocated anyway. But sometimes if the ''execv'' fails the program has
to do something else and the argv should be deallocated.
For that the library provides the following function:
void s2argv_free(char **argv);

So a code snippet to execute a file from a string (''buf'' in this example) is the following:
char **argv=s2argv(buf, NULL);
execvp(argv[0], argv);
s2argv_free(argv);
printf("exec error0);

==execs and siblings==
The library provides three functions:
int execs(const char *path, char *args);
int execsp(char *args);
int execspe(char *args, char *const envp[]);

they have been designed as the "parse args from a string" counterpart of ''execv'', ''execvp'' and ''execvde'' respectively.

These functions do not use dynamic allocation and '''modify''' their ''args'' parameter. So in case you need to reuse the
''args'' string in case of failure, backup the ''args'' string in advance or use ''s2argv'' instead.

The return value and error cases are the same as ''execve''. ''execsp'' and ''execspe'' use the parsed argv[0] as the filename.

@@ Riga 59: / Riga 59: @@
 The return value and error cases are the same as ''execve''. ''execsp'' and ''execspe'' use the parsed argv[0] as the filename.
-Here is a chung of code using execsp:
+Here is a chunk of code using execsp:
              char buf[BUFLEN];

@@ Riga 62: / Riga 62: @@
              char buf[BUFLEN];
-             printf("type in a command and its arguments, e.g. 'ls -l'0);
+             printf("type in a command and its arguments, e.g. 'ls -l'\n");
              if (fgets(buf, BUFLEN, stdin) != NULL) {
                   execsp(buf);
-                  printf("exec error0);
+                  printf("exec error\n");
+             }

← Versione meno recente		Versione delle 14:14, 27 mag 2014
Riga 58:		Riga 58:

	The return value and error cases are the same as ''execve''. ''execsp'' and ''execspe'' use the parsed argv[0] as the filename.		The return value and error cases are the same as ''execve''. ''execsp'' and ''execspe'' use the parsed argv[0] as the filename.
		+
		+	Here is a chung of code using execsp:
		+
		+	char buf[BUFLEN];
		+	printf("type in a command and its arguments, e.g. 'ls -l'0);
		+	if (fgets(buf, BUFLEN, stdin) != NULL) {
		+	execsp(buf);
		+	printf("exec error0);
		+	}

@@ Riga 27: / Riga 27: @@
 ==s2argv==
 convert the string in a dynamically allocated argv using s2argv (string to argv):
-char **s2argv(const char *args, int *pargc);
+  char **s2argv(const char *args, int *pargc);
 The return value is a valid argv, if ''pargc'' is non-NULL, the number of args, i.e. the argc, is stored in the integer field pointed to by ''pargc''. ''s2argv'' uses dynamic allocation and does not modify its input parameter ''args''.

@@ Riga 3: / Riga 3: @@
 Some of them can take a variable number of args, others use an array of strings. The formers have a name having an 'l' in the suffix, the latters a 'v'.
-But what do you do if you have a string including all the arguments separated by spaces.
+But what do you do if you have a string including all the arguments separated by spaces?
-This is the case, for instance, when the command has been provided by the user or read from a file.
+This is the case, for instance, when the command has been provided by the user at an input prompt or read from a file.
 It happened to me dozens of times.
@@ Riga 10: / Riga 10: @@
 There are two naive solutions. ''strtok'' and ''system''.
 ''strtok'' can be usen to tokenize the string, ''system'' delegates the problem to a shell.
-Both solutions are unsitisfactory to me.
+Both solutions are unsatisfactory to me.
-''system'' is unsafe (it is stated also on its man page!). ''strtok'' use spaces to split the string into pieces, modify the original string, do not support quotation or escape characters, It is also very annoying to use ''strtok'' to parse the arguments for an ''exec''.
+''system'' is unsafe (it is stated also on its own man page!). ''strtok'' use spaces to split the string into pieces, modify the original string, do not support quotation or escape characters, It is also very annoying to use ''strtok'' to parse the arguments for an ''exec''.
 I needed a clean solution to parse the arguments from a string.
-So I decided to write the libs2argv library. (200 lines of C source).
+So I decided to develop the libs2argv library. (200 lines of C source).
 It is not a historical achievement in the story of computing, but it is something that was missing and I felt the need for.

@@ Riga 44: / Riga 44: @@
                   execvp(argv[0], argv);
                   s2argv_free(argv);
-                  printf("exec error0);
+                  printf("exec error\n");
 ==execs and siblings==