Bash manual saysThe first word of the replacement text is tested for aliases, but a  word that is identical to an alias being expanded is not expanded a  second time. This means that one may alias ls to ls -F, for  instance, and Bash does not try to recursively expand the replacement  text.I'm trying to figure out which alias follows identical to in the quote, any alias being expanded in the same sequence of alias expansion recursions, or the alias whose expansion was first started, or the alias whose expansion was last started.So I create  an example$ alias a1=a2; $ alias a2=a3;$ alias a3=a4;and want to check the alias expansion result of a1, in the following cases$ alias a4=a1;or$ alias a4=a2;or$ alias a4=a3;How can I check the alias expansion result of a1, possibly by performing alias expansion on a1 without letting the shell going further than alias expansion?
a word that is identical to an alias being expanded is not expanded a second time
bash;shell;alias
What the manual says is that the shell will avoid any loop that may be caused by recursion of alias expansion.With your example (a1=a2=a3=a4), if you execute alias a4=a1 you are creating a loop. Then, as soon as you will execute a1 (resp. a2, a3, a4), once the shell loops back to a1 (resp. a2, a3, a4) it will search for a command named a1 (resp. a2, a3, a4) that is NOT an alias (since that would create a never-ending loop).Example:$ a1() { echo Phew, I got out of the loop; }$ alias a1='echo (a1); a2' a2='echo (a2); a3'$ alias a3='echo (a3); a4' a4='echo (a4); a1'$ a1(a1)(a2)(a3)(a4)Phew, I got out of the loop$ a2                              # Command a2 does not exist anywhere(a2)(a3)(a4)(a1)a2: command not found