A Bash script to check if a string is present in a comma separated list of strings

Question

I would like to know a neat way in which I can check to see if a string is there in a comma separated value of strings. eg: if

x="abc,def,ghi"
y="abc"

it should return true

and if

y="ab"

then it should return false

Answer 1

You could use globs:

[[ ",$x," = *",$y,"* ]]

Answer 2

Use bash's regular-expression-matching operator, =~:

[[ $x =~ (^|,)"$y"(,|$) ]]

Caveat: While the above regex happens to be portable, the particular flavor of regular expressions supported by =~ is platform-dependent due to use of a given platform's regex libraries.

Case in point: hek2mgl suggests use of \b to match word boundaries, which works on Linux, but not OSX, for instance. The closest thing to \b in POSIX are [[:<:]] and [[:>:]], but, unfortunately, these don't work on Linux.