CODEWITHSUNDEEP
cawk
dejunl
dejunl

Reputation: 57

'system' to 'fork+execv' when dealing with awk command

1)After solving the question: How to translate 'system()' call to 'fork() + execl()' when dealing with awk command?

2)I encounter another problem according to melpomene's method:

#define LOG_FILE_PATH "/tmp/logfile"
system("awk -v FS=\"[][]\" -v BEGINTIME=\"$BEGINTIME\" -v ENDTIME=\"$ENDTIME\" '$2>=BEGINTIME && $2<=ENDTIME' "LOG_FILE_PATH);

it works fine and I get what I want.

3)Translate to fork+execl version:

sprintf(tmp1, "BEGINTIME=%s", getenv("BEGINTIME"));
sprintf(tmp2, "ENDTIME=%s", getenv("ENDTIME"));
sprintf(tmp3, "$2>=%s && $2<=%s", getenv("BEGINTIME"), getenv("ENDTIME"));
execl("/usr/bin/awk", "awk", "-v", "FS=\"[][]\"", "-v", tmp1, "-v", tmp2, tmp3, LOG_FILE_PATH, (char *)0);

it outputs nothing, why?

Upvotes: 0

Views: 430

Answers (2)

William Pursell
William Pursell

Reputation: 212268

Because tmp 3 should include the literal text BEGINTIME and ENDTIME. Try:

sprintf( tmp3, "$2>=%s && $2<=%s", "BEGINTIME", "ENDTIME" );

Also, you probably want to keep the double quotes in tmp1 and tmp2:

sprintf(tmp1, "BEGINTIME=\"%s\"", getenv("BEGINTIME"));

and you really need to check that the environment variables are actually set.

Also, you are setting FS incorrectly. In the system version, awk gets the argument FS=[][] (the shell strips the double quotes before it invokes awk.) So the argument passed to execl should be "FS=[][]"

Upvotes: 2

Ed Morton
Ed Morton

Reputation: 203684

If you're on Solaris then /usr/bin/awk is old, broken awk which among it's many other issues does not support -v for variable assignment.

Also, awk programs are delimited by a quotation character so I THINK you should be doing something like this:

sprintf(tmp3, "\'$2>=%s && $2<=%s\'", ...);

instead of this:

sprintf(tmp3, "$2>=%s && $2<=%s", ...);

Upvotes: 0

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