The fstequal command exits with a return code indicating whether or not the two compiled fsts passed in are equivalent. The return code will be 0 if they are equal, and nonzero if they are not.

The easiest way to see the return code is to type `echo $?` immediately after executing fstequal. This command shows the return code of the last executed command, and thus will show you a 0 if the two fsts are equal. For example, let’s c
onsider a perfectly straight fst:

jms852@kay:~$ fstprint straight.fst
0 0 0 0
0 1 1 0
1 2 0 0
2 3 0 0
3 3 0 0
3 3 1 0
jms852@kay:~$ fstequal straight.fst straight.fst
jms852@kay:~$ echo $?
0

Then let’s add another fst that forks off instead of continuing straight, and compare that one:

jms852@kay:~$ fstprint fork.fst
0 0 0 0
0 1 1 0
1 2 0 0
2 3 0 0
2 4 1 0
3 Infinity
4 Infinity
jms852@kay:~$ fstequal straight.fst fork.fst
jms852@kay:~$ echo $?
2

Two fsts can be equivalent even if they are not the exact same file, or if their edges are labelled differently. For example, if I create straight2.fst:

jms852@kay:~$ cat straight.txt
0 0 0 0

0 2 1 0

2 1 0 0

1 3 0 0

3 3 0 0

3 3 1 0

You can see that it is still straight, but the nodes have different labels.

However, we see that fstequal still says that they are equal

jms852@kay:~$ fstequal straight.fst straight2.fst
jms852@kay:~$ echo $?
0