Bash – How to test if a particular alias is defined

After some testing, I have concluded the following:

• Aliases only work in interactive mode (add -i to the shebang).
• Aliases are not evaluated when they come from an interpreted source (in this case, the variable.
• You can get bash to use the alias with eval $1. Note that evaling anything created with a variable is dangerous, but since the whole point of the script requires arbitrary execution, I won't make too big a deal out of that.

From the bash man page:

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see the description of shopt under SHELL BUILTIN COMMANDS below).

So you could add shopt -s expand_aliases instead of -i.

Also,

Aliases are expanded when a command is read, not when it is executed.

Since variables are not expanded before the command is read, they will not be expanded further using the alias.

To find out what commands are masked by aliases, do something like this:

alias | sed 's/^[^ ]* *\|=.*$//g' | while read a; do
  printf "%20.20s : %s\n" $a "$(type -ta $a | tr '\n' ' ')"
done | awk -F: '$2 ~ /file/'

Explanation

alias alone lists defined aliases and sed extracts their name. The while loop runs type -ta on each of them and awk prints the lines that both contain alias and file.