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Because execl's first argument isn't argv[0]. execl("/bin/sh", "-c", ...) runs the executable /bin/sh, but sets its argv[0] to "-c", as if one had created a link called -c pointing at it and run t...
Answer
#1: Initial revision
by
Emily
·
2024-03-11T04:21:45Z (9 months ago)
**Because `execl`'s first argument isn't `argv[0]`.**
`execl("/bin/sh", "-c", ...)` runs the executable `/bin/sh`, but sets its `argv[0]` to `"-c"`, as if one had created a link called `-c` pointing at it and run that. **The correct way to do this is `execl("/bin/sh", "sh", "-c", ...)`**.
Busybox works here by accident, because it has `sh` as its `argv[0]`: its `argv` when executed as I did in my last example would be `{"sh", "-c", "echo hello world"}`. Busybox, specifically, actually does support being called like that (a normal way to use busybox is to install it somewhere and then symlink all the commands it supports, including `sh`, to it).