macOS not grep

[farmerdoug]

If grep fails to find a file it prints out an error message. Neither redirecting the output of grep

 strcpy(grep, "grep        \"");
            strcat(grep, date2[d]);
            strcat(grep, ",1552\" ");
            strcat(grep, dir);
            strcat(grep, &ratios[i*pagesize]);
            strcat(grep, ".txt > \"out.txt\"");
            corncob = popen(grep, "r");
            fgets(buf,100,corncob);
            pclose(corncob);

nor redirecting the output of the program

./code > "out.txt"

gets me a list of the files it can't find. Any suggestions on how to do that?

 

[farmerdoug]

not grep part 2

If I use ls file | wc, I can tell if the file exists. How do I get the values out of wc?

 

[mslide]

Is your goal to redirect those grep error messages (about the fact that it can't find certain files) to another file? The standard redirect symbol ( > ) with nothing else only redirects stuff sent to the standard output stream. Error messages (like messages about the fact that grep can't find a certain file) are sent to the standard error stream and are redirected differently.

Here are a few examples:

Redirect normal results and errors:

grep foo bar > results_and_errors.txt 2>&1

A simplified version of the above command is (which may not work on all types of shells):

grep foo bar >& results_and_errors.txt

Redirect errors only:

grep foo bar 2> errors_only.txt

The "Redirection (computing)" wikipedia article has a lot of good info about this. I hope this is what you were asking.

 

[farmerdoug]

I search google but didn't think to search redirection.
Method 3 worked for me.
Thanks