“l” suffix

For example, if I want to invoke the ls command with the arguments -t, -r, and -l (meaning “sort the output by time, in reverse order, and show me the long version of the output”), I could specify it as either:

/* To run ls and keep going: */
spawnl (P_WAIT, "/bin/ls", "/bin/ls", "-t", "-r", "-l", NULL);

/* To transform into ls: */
execl ("/bin/ls", "/bin/ls", "-t", "-r", "-l", NULL);

or, using the v suffix variant:

char *argv [] =

/* To run ls and keep going: */
spawnv (P_WAIT, "/bin/ls", argv);

/* To transform into ls: */
execv ("/bin/ls", argv);

Why the choice? It's provided as a convenience. You may have a parser already built into your program, and it would be convenient to pass around arrays of strings. In that case, I'd recommend using the v suffix variants. Or, you may be coding up a call to a program where you know what the parameters are. In that case, why bother setting up an array of strings when you know exactly what the arguments are? Just pass them to the l suffix variant.

Note that we passed the actual pathname of the program (/bin/ls) and the name of the program again as the first argument. We passed the name twice to support programs that behave differently based on how they're invoked.

For example, the GNU compression and decompression utilities (gzip and gunzip) are actually links to the same executable. When the executable starts, it looks at argv [0] (passed to main()) and decides whether it should compress or decompress.