Fscanf not reading the entire popen

Question

I would like to ask if anyone know why when i put the code like this:

            char buff[100];
            FILE *pf = popen("/bin/file ola.png", "w");
            fscanf(pf, "%s", buff);
            pclose(pf);

It prints: ola.png: Zip archive data, at least v1.0 to extract

And if i put:

            char buff[100];
            FILE *pf = popen("/bin/file ola.png", "r");
            fscanf(pf, "%s", buff);
            pclose(pf);
            printf("%s", buff);

it prints just: ola.png:

I would like it to save the entire phrase on the buffer, not just ola.png:

Thank you!

`fscanf` only reads till the first whitespace. Either use `fgets` in a loop, or `fread` to read everything at once. — Eugene Sh., Nov 04 '21 at 17:22
"It prints: ola.png: Zip archive data, at least v1.0 to extract" --> output may have been on `stderr`. — chux - Reinstate Monica, Nov 04 '21 at 18:20

chux - Reinstate Monica · Answer 1 · 2021-11-04T20:17:25.430

save the entire phrase on the buffer

The "%s" in char buff[100]; ... fscanf(pf, "%s", buff); directs code¹ to:

Read and skip any leading white-spaces.
Read and save 1 or more non-white-spaces into buff - possibly overrunning buff.
Continue until reading a white-space (like '\n'), put it back into pf and then append a '\0' to buff.

This does not read an entire line of input. More like one "word". It is also worse than gets lacking a width limit like "%99s".

Instead use fgets() to read a line into a string. Result includes any '\n'.

if (fgets(buff, sizeof buff, pf)) Success();

¹ some details omitted for brevity. C17dr spec details.

Fscanf not reading the entire popen

1 Answers1