can you expand on this? does this elucidate, e.g., variable substitution and the difference between single- and double-quotes? or does it just help demonstrate when you need quotes for an argument that may contain whitespace?
For example, all the various wrong ways of quoting var="My File.txt" or otherwise incorrectly using such a name will result in variations on a wrong argument list:
execlp("cat", "$var", NULL); // cat '$var'
execlp("cat", "My", "File.txt", NULL); // cat $var
execlp("cat My File.txt", NULL); // cmd="cat $var"; "$cmd"
execlp("cat", "'My", "File.txt'", NULL);// cmd="cat '$var'"; $cmd
execlp("cat", "My\\", "File.txt", NULL);// cmd="cat My\ File.txt"; $cmd
execlp("cat", "'My File.txt'", NULL); // var="'$var'"; cat "$var"
execlp("cat", "\"$var\"", NULL); // arg='"$var"'; cat $arg
execlp("cat", "My File.txt", NULL); // cat "$var"
execlp("cat", "My File.txt", NULL); // cat 'My File.txt'
execlp("cat", "My File.txt", NULL); // cat "My File.txt"
execlp("cat", "My File.txt", NULL); // cat My\ File.txt
execlp("cat", "My File.txt", NULL); // cmd=("cat" "$var"); "${cmd[@]}"
execlp("cat", "My File.txt", NULL); // arg="'My File.txt'"; eval "cat $arg"
Do you recommend a book or something like that? And preferably for a beginner?
Love - Linux System Programming
The Unix-Haters Handbook
(Unfortunately, the best resource ever for this kind of stuff, from which I learned, does not have an English translation.)
I might translate them some day and put them up on the Internet (if I get his permission and some free time).
Bash is essentially a DSL for these. A lot of the weirdness you see in the language is due to these abstractions leaking through. For example:
* Quoting is building execve's argv parameter. It's hard to quote correctly if you don't know what exactly you're working towards.
* Redirections are opening and copying file descriptors. It explains their scope, order and nesting behavior.
* Variables are modifying and passing the environment, and their weird scope is due to forks imposed by the process model.
Once you know how you can do whatever you want in C through the basic syscalls, Bash is an extremely efficient and far less surprising shortcut to do it.