shellscript in C: using awk getting runaway string constant error - c

Question

#define SHELLSCRIPT "\
#/bin/bash \n\
awk 'BEGIN { FS=\":\"; print \"User\t\tUID\n--------------------\"; } { print $1,\"\t\t\",$3;} END { print \"--------------------\nAll Users and UIDs Printed!\" }' /etc/passwd \n\
"
void displayusers()
{
system(SHELLSCRIPT);
}
The error message is:
awk: line 1: runaway string constant "User...
The bash cmd when run and works in the terminal is:
awk 'BEGIN { FS=":"; print "User\t\tUID\n--------------------"; } { print $1,"\t\t",$3;} END { print "--------------------\nAll Users and UIDs Printed!" }' /etc/passwd
I think somewhere when using \ to block out the various " for c it messed up my awk. But I'm not sure where. Ideas?

Answer 1

I simply took your string and used it in a printf() statement, and then analyzed the output:
#include <stdio.h>
#define SHELLSCRIPT "\
#/bin/bash \n\
awk 'BEGIN { FS=\":\"; print \"User\t\tUID\n--------------------\"; } { print $1,\"\t\t\",$3;} END { print \"--------------------\nAll Users and UIDs Printed!\" }' /etc/passwd \n\
"
int main(void)
{
printf("[[%s]]\n", SHELLSCRIPT);
return 0;
}
Example run:
$ ./runaway
[[#/bin/bash
awk 'BEGIN { FS=":"; print "User UID
--------------------"; } { print $1," ",$3;} END { print "--------------------
All Users and UIDs Printed!" }' /etc/passwd
]]
$
When I made the line ends visible (^J marks the end of line, ^I tabs), the problem is transparent:
[[#/bin/bash ^J
awk 'BEGIN { FS=":"; print "User^I^IUID^J
--------------------"; } { print $1,"^I^I",$3;} END { print "--------------------^J
All Users and UIDs Printed!" }' /etc/passwd ^J
]]^J
You have two occurrences of \n in the string which need to be \\n. It is up to you whether you change the appearances of \t to \\t; it works either way.
#define SHELLSCRIPT "\
#/bin/bash\n\
awk 'BEGIN { FS=\":\"; print \"User\t\tUID\\n--------------------\"; } { print $1,\"\t\t\",$3;} END { print \"--------------------\\nAll Users and UIDs Printed!\" }' /etc/passwd\n"
Using that in my program yields:
[[#/bin/bash^J
awk 'BEGIN { FS=":"; print "User^I^IUID\n--------------------"; } { print $1,"^I^I",$3;} END { print "--------------------\nAll Users and UIDs Printed!" }' /etc/passwd^J
]]^J
Note, in particular, the technique used to debug this. Print the data so you can see it precisely.

Answer 2

Haven't tested, but here's a useful-looking article just about this topic and it would appear that your choices are something along the following lines:
if you have different quotes surrounding the text, you don't need to escape the interior ones
you can use the same quotes surrounding and escape the interior ones
you can use octal sequences for the quotes, e.g. <\42>
if it get's too confusing, move the string into a separate file where quoting will not be an issue