I would like to know if there is any man page documenting the construction of the most basic script commands like if/then/else, while, for each, and all the relative switches, like -eq, -e, -ge, and so on.
if/then/else man page
shell;scripting;man;documentation
You have to look at the manual for the specific shell you are using as the exact syntax for using these constructs can vary between shells. Most likely you are using bash, so you would do man bash. Although there are many cases where you might be using something else. For example many distros use a POSIX shell for boot scripts (eg Debian uses dash) or a least use bash in POSIX compliant mode. Usually you can do man sh to get the documentation in this case (this will be linked to the man page for the shell used if it is not the original sh or Bourne shell).If you are unsure which shell you are using, see this question - determine shell in script during runtimeAnother thing work mentioning is the help builtin for bash, it gives an abbreviated version of what is in the manual for the various builtin commands/flow control statements etc. You can use help on its own to see a full list of what is available, otherwise you can try things like help if, help for, help test and help [.