Unexpected behavior of expr

Question

Hi all,
It may sound a bit trivial but it actually is quite frustrating: Can anyone explain me this:

[~:user$]expr 3 + 2
6
[~:user$]expr 3 / 2
1
[~:user$]expr 3 * 2
expr: syntax error

When the man page for expr precisely specifies that ARG1 * ARG2 is arithmetic product of both.

Thanks,

Answer 1

You need to quote the *, because otherwise the shell attempts file name expansion.

$ expr 3 '*' 2
6

Answer 2

* is expanded by your shell before it reaches expr, therefore it contains Documents, Videos, Work, nsfw, etc.

Answer 3

@OP, its entirely up to you, but i would still suggest to use shell internal addition operation instead of calling external expr

$ echo $(( 3*2 ))
6

If you require more advance maths operations, use bc(dc) or awk.

Answer 4

This should be enough:

expr 3 \* 2