set
is showing you all environmental variables and builtin functions that exist on your machine and in your shell among other information gathered.
If you want to know the full story, check the source code for the builtin.
To address your example, update_terminal_cwd
is in the default systemwide .bashrc file:
# System-wide .bashrc file for interactive bash(1) shells.
if [ -z "$PS1" ]; then
return
fi
PS1='\h:\W \u\$ '
# Make bash check its window size after a process completes
shopt -s checkwinsize
# Tell the terminal about the working directory at each prompt.
if [ "$TERM_PROGRAM" == "Apple_Terminal" ] && [ -z "$INSIDE_EMACS" ]; then
update_terminal_cwd() {
# Identify the directory using a "file:" scheme URL,
# including the host name to disambiguate local vs.
# remote connections. Percent-escape spaces.
local SEARCH=' '
local REPLACE='%20'
local PWD_URL="file://$HOSTNAME${PWD//$SEARCH/$REPLACE}"
printf '\e]7;%s\a' "$PWD_URL"
}
PROMPT_COMMAND="update_terminal_cwd; $PROMPT_COMMAND"
fi
/etc/bashrc
.