"So this is probably a long shot, but is there any way to run a C or C++ file as a script"
With gcc it is not so straight forward, but with the tiny C compiler tcc this is easy, e.g.:
File: hw.c
#!/usr/local/bin/tcc -run #include <stdio.h> int main() { printf("Hello, world!\n"); return 0; }
In Algol68g (my weekend extreme sport language) this is "reasonably" easy... mostly because a "#comment#" is native to the Algol68 language. e.g. here is an implementations of the classic echo command.
File: echo.a68
#!/usr/bin/a68g --script # # -*- coding: utf-8 -*- # STRING ofs := ""; FOR i FROM 4 TO argc DO print((ofs, argv(i))); ofs:=" " OD
But how can we natively do this in C with gcc? ...
Simple shebangs can help with scripting, e.g. "#!/usr/bin/env python" at the top of a Python script will allow it to be run in a terminal as "./script.py".
The task Multiline shebang largely demonstrates how to use "shell" code in the shebang to compile and/or run source-code from a 3rd language.
However in this task Native shebang task we are go native. In the shebang, instead of running a shell, we call a binary-executable generated from the original native language, e.g. when using C with gcc "#!/usr/local/bin/script_gcc" to extract, compile and run the native "script" source code.
Other small innovations required of this Native shebang task:
- Cache the executable in some appropriate place in a path, dependant on available write permissions.
- Generate a new cached executable only when the source has been touched.
- If a cached is available, then run this instead of regenerating a new executable.
- Naturally, some languages are not compiled. These languages are forced to use shebang executables from another language, eg "#!/usr/bin/env python" uses the C binaries /usr/bin/env and /usr/bin/python. If this is the case, then simply document the details of the case.
- In a perfect world, the test file (e.g. echo.c) would still be a valid program, and would compile without error using the native compiler (e.g. gcc for text.c). The problem is that "#!" is syntactically incorrect on many languages, but in others it can be parsed as a comment.
- The "test binary" should be exec-ed and hence retain the original Process identifier.
- Create a simple "script file" (in the same native language) called "echo" then use the "script" to output "Hello, world!"
C
File: script_gcc.c#!/usr/local/bin/script_gcc.sh /* Optional: this C code initially is-being/can-be boot strapped (compiled) using bash script_gcc.sh */ #include <errno.h> #include <libgen.h> #include <stdarg.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/stat.h> #include <unistd.h> /* the actual shebang for C target scripts is: #!/usr/local/bin/script_gcc.c */ /* general readability constants */ typedef char /* const */ *STRING; typedef enum{FALSE=0, TRUE=1} BOOL; const STRING ENDCAT = NULL; /* script_gcc.c specific constants */ #define DIALECT "c" /* or cpp */ const STRING CC="gcc", COPTS="-lm -x "DIALECT, IEXT="."DIALECT, OEXT=".out"; const BOOL OPT_CACHE = TRUE; /* general utility procedured */ char strcat_out[BUFSIZ]; STRING STRCAT(STRING argv, ... ){ va_list ap; va_start(ap, argv); STRING arg; strcat_out[0]='\0'; for(arg=argv; arg != ENDCAT; arg=va_arg(ap, STRING)){ strncat(strcat_out, arg, sizeof strcat_out); } va_end(ap); return strndup(strcat_out, sizeof strcat_out); } char itoa_out[BUFSIZ]; STRING itoa(int i){ sprintf(itoa_out, "%d", i); return itoa_out; } time_t modtime(STRING filename){ struct stat buf; if(stat(filename, &buf) != EXIT_SUCCESS)perror(filename); return buf.st_mtime; } /* script_gcc specific procedure */ BOOL compile(STRING srcpath, STRING binpath){ int out; STRING compiler_command=STRCAT(CC, " ", COPTS, " -o ", binpath, " -", ENDCAT); FILE *src=fopen(srcpath, "r"), *compiler=popen(compiler_command, "w"); char buf[BUFSIZ]; BOOL shebang; for(shebang=TRUE; fgets(buf, sizeof buf, src); shebang=FALSE) if(!shebang)fwrite(buf, strlen(buf), 1, compiler); out=pclose(compiler); return out; } void main(int argc, STRING *argv, STRING *envp){ STRING binpath, srcpath=argv[1], argv0_basename=STRCAT(basename((char*)srcpath /*, .DIALECT */), ENDCAT), *dirnamew, *dirnamex; argv++; /* shift */ /* Warning: current dir "." is in path, AND * /tmp directories are common/shared */ STRING paths[] = { dirname(strdup(srcpath)), /* not sure why strdup is required? */ STRCAT(getenv("HOME"), "/bin", ENDCAT), "/usr/local/bin", ".", STRCAT(getenv("HOME"), "/tmp", ENDCAT), getenv("HOME"), STRCAT(getenv("HOME"), "/Desktop", ENDCAT), /* "/tmp" ... a bit of a security hole */ ENDCAT }; for(dirnamew = paths; *dirnamew; dirnamew++){ if(access(*dirnamew, W_OK) == EXIT_SUCCESS) break; } /* if a CACHEd copy is not to be kept, then fork a sub-process to unlink the .out file */ if(OPT_CACHE == FALSE){ binpath=STRCAT(*dirnamew, "/", argv0_basename, itoa(getpid()), OEXT, ENDCAT); if(compile(srcpath, binpath) == EXIT_SUCCESS){ if(fork()){ sleep(0.1); unlink(binpath); } else { execvp(binpath, argv); } } } else { /* else a CACHEd copy is kept, so find it */ time_t modtime_srcpath = modtime(srcpath); for(dirnamex = paths; *dirnamex; dirnamex++){ binpath=STRCAT(*dirnamex, "/", argv0_basename, OEXT, ENDCAT); if((access(binpath, X_OK) == EXIT_SUCCESS) && (modtime(binpath) >= modtime_srcpath)) execvp(binpath, argv); } } binpath=STRCAT(*dirnamew, "/", argv0_basename, OEXT, ENDCAT); if(compile(srcpath, binpath) == EXIT_SUCCESS) execvp(binpath, argv); perror(STRCAT(binpath, ": executable not available", ENDCAT)); exit(errno); }Test Source File: echo.c
#!/usr/local/bin/script_gcc.c #include <stdio.h> #include <string.h> #include <stdlib.h> int main(int argc, char **argv, char **envp){ char ofs = '\0'; for(argv++; *argv; argv++){ if(ofs)putchar(ofs); else ofs=' '; fwrite(*argv, strlen(*argv), 1, stdout); } putchar('\n'); exit(EXIT_SUCCESS); }Test Execution:
$ ./echo.c Hello, world!Test Output:
Hello, world!
UNIX Shell
Note: this Native shebang task does not exactly apply to bash because bash is interpretive, but as a skeleton template the following script is an example of how compiled languages can implement the shebang. Also: this bash code can be used to automatically compile the C code in /usr/local/bin/script_gcc.c above.File: script_gcc.sh
#!/bin/bash # Actual shebang when using bash: #!/usr/local/bin/script_gcc.sh # Alternative shebang when using bash: #!/bin/bash /usr/local/bin/script_gcc.sh # CACHE=No # to turn off caching... # Note: this shell should be re-written in actual C! :-) DIALECT=c # or cpp CC="gcc" COPTS="-lm -x $DIALECT" IEXT=.$DIALECT OEXT=.out ENOENT=2 srcpath="$1"; shift # => "$@" #basename="$(basename "$srcpath" ."$DIALECT")" basename="$(basename "$srcpath")" # Warning: current dir "." is in path, AND */tmp directories are common/shared paths="$(dirname "$srcpath") $HOME/bin /usr/local/bin . $HOME/tmp $HOME $HOME/Desktop" #/tmp while read dirnamew; do [ -w "$dirnamew" ] && break done << end_here_is $paths end_here_is compile(){ sed -n '2,$p' "$srcpath" | "$CC" $COPTS -o "$binpath" - } if [ "'$CACHE'" = "'No'" ]; then binpath="$dirnamew/$basename-v$$$OEXT" if compile; then ( sleep 0.1; exec rm "$binpath" ) & exec "$binpath" "$@" fi else while read dirnamex; do binpath="$dirnamex/$basename$OEXT" if [ -x "$binpath" -a "$binpath" -nt "$srcpath" ]; then exec "$binpath" "$@"; fi done << end_here_is $paths end_here_is binpath="$dirnamew/$basename$OEXT" if compile; then exec "$binpath" "$@"; fi echo "$binpath: executable not available" 1>&2 exit $ENOENT fi
Test Source File: echo.c
#!/usr/local/bin/script_gcc.sh #include <stdio.h> #include <string.h> #include <stdlib.h> int main(int argc, char **argv, char **envp){ char ofs = '\0'; for(argv++; *argv; argv++){ if(ofs)putchar(ofs); else ofs=' '; fwrite(*argv, strlen(*argv), 1, stdout); } putchar('\n'); exit(EXIT_SUCCESS); }Test Execution:
$ ./echo.c Hello, world!Test Output:
Hello, world!
Here is a summary of the input script files, together with binary files generated:
$ ls -ltr hw.* echo.* /usr/local/bin -rwxr-xr-x. 1 nevillednz nevillednz 193 Sep 6 13:17 hw.c -rwxr-xr-x. 1 nevillednz nevillednz 4757 Sep 6 13:18 hw.c.out -rwxr-xr-x. 1 nevillednz nevillednz 131 Sep 6 13:19 echo.a68 -rwxr-xr-x. 1 nevillednz nevillednz 12373 Sep 6 13:20 echo.so -rwxr-xr-x. 1 nevillednz nevillednz 315 Sep 6 13:29 echo.c -rwxr-xr-x. 1 nevillednz nevillednz 5128 Sep 6 13:30 echo.c.out /usr/local/bin: total 20 -rwxr-xr-x. 1 nevillednz nevillednz 1216 Sep 6 13:13 script_gcc.sh -rwxr-xr-x. 1 nevillednz nevillednz 3431 Sep 6 13:15 script_gcc.c -rwxr-xr-x. 1 nevillednz nevillednz 8564 Sep 6 13:16 script_gcc.c.out
One interesting thing to observe is that "script_gcc.c" is boot strapped by "script_gcc.sh", so as long as gcc is installed, you don't have to compile anything... not even the script_gcc.c "script"... (But you do have to have the right permissions to start off with!)
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