What is the difference between $(()) and expr?

Question

What is the main difference between $(()) and expr in Unix-Like systems?

`$(())` is for bash arithmetic. expr is for evaluating expressions, this can be arithmetic or strings. Looking in the bash man page for `$(())` and the `expr` man page will tell you everything both commands can do. — 123, Jun 08 '16 at 10:50
Not just bash arithmetic. `$(( ))` has been in the POSIX sh spec since it was published in 1991. — Charles Duffy, Jun 22 '16 at 14:44

score 3 · Accepted Answer · edited Jun 22 '16 at 14:42

3

$(()) will almost certainly be within the shell that you are using. expr may be an external call

edited Jun 22 '16 at 14:42

gniourf_gniourf

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answered Jun 08 '16 at 10:46

Pwl256

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Both are specified by POSIX. You might be able to construct a scenario where it is useful to use a command rather than built-in syntax for arithmetic, but by and large `$((...))` has replaced `expr` for all but regular expressions. – chepner Jun 08 '16 at 11:30

score 0 · Answer 2 · answered Jun 22 '16 at 14:37

expr is a holdover from the early days of the Bourne shell. You should avoid expr unless you are forced to create scripts which need to be interoperable with legacy (pre-POSIX) sh implementations. (It's not too long ago since Solaris sh fell into this category, for example.)

What is the difference between $(()) and expr?

2 Answers2