improve the sample run

modules/warm-up/grep.md

@@ -10,7 +10,15 @@ program will match a single string which is hard-coded in the program
 in the form of (boundless) array (`char needle[] = "foobar";`).
 The program will use `getchar()` to read the characters from the standard input.
 
-Sample program run:
+Sample program run (with the search string hard-coded as `bash`):
+```
+$ cat /etc/passwd | ./a.out
+root:x:0:0:root:/root:/bin/bash
+foo:x:1000:1000:Foo,,,:/home/foo:/bin/bash
+backu:x:1001:1001:backup,,,:/home/backu:/bin/bash
+perforce:x:133:141:Perforce Admin:/opt/perforce:/bin/bash
+```
+compared to the fgrep(1) utility:
 ```
 $ fgrep bash /etc/passwd
 root:x:0:0:root:/root:/bin/bash