What's the difference between "env" and "set" (on Mac OS X or Linux)? [closed]

Question

I get similar results running "env" and "set". Set gives more results - is it a superset of env?

The man page for set doesn't give any information. How do these commands work and what's the difference?

Answer 1

Long story short: set can see shell-local variables, env cannot.

Shells can have variables of 2 types: locals, which are only accessible from the current shell, and (exported) environment variables, which are passed on to every executed program.

Since set is a built-in shell command, it also sees shell-local variables (including shell functions). env on the other hand is an independent executable; it only sees the variables that the shell passes to it, or environment variables.

When you type a line like a=1 then a local variable is created (unless it already existed in the environment). Environment variables are created with export a=1

Answer 2

If you want to limit the output of the set command to variables only, you may run it in POSIX mode:

type -a env set help set (set -o posix; set) | nl 

If you need finer control over listing specific variables, you may use Bash builtins such as declare or compgen, or some other Bash tricks.

man bash | less -p '-A action$'  # info on complete & compgen  # listing names of variables compgen -A variable | nl       # list names of all shell variables echo ${!P*}                    # list names of all variables beginning with P  compgen -A export | nl         # list names of exported shell variables export | nl                    # same, plus always OLDPWD declare -px | nl               # same  declare -pr                    # list readonly variables  # listing names of functions            compgen -A function | nl declare -F | nl declare -Fx | nl  # show code of specified function myfunc() { echo 'Hello, world!'; return 0; } declare -f myfunc