matching text in brackets

Question

A fairly simple goal - I thought: matching text in brackets which contains two comma-separated parts, like e.g.:
[first,second] That's the whole line, I used bash 4.1.

I tried a pattern match like this and tried to use BASH_REMATCH afterwards:

[[ "$file_contents" =~ ^[\ []\(.*\),\(.*\)\ []\ ]$ ]] && echo YES || echo NO

I tried several little modifications but got either no match at all or wrong contents of BASH_REMATCH.

What's wrong about the regular expression above?

Answer 1

This works in bash 3.2.25(1) from CentOS 5 but fails in bash 4.1.2(1) from CentOS 6:

$ file_contents="[word1 word2,word3 word4]"
$ [[ $file_contents =~ ^\\[([^,]+),([^]]+)\\] ]]; echo $?
0
$ declare -p BASH_REMATCH
declare -ar BASH_REMATCH='([0]="[word1 word2,word3 word4]" [1]="word1 word2" [2]="word3 word4")'

• Start of string: ^
• Literal open square bracket: \\[
• Capture start: (
• One or more of class of anything but comma: [^,]+
• Capture end: )
• Literal comma: ,
• Capture start: (
• One or more of class of anything but close square bracket: [^]]+
• Capture end: )
• Literal close square bracket: \\]

This works in bash 4.1.2(1) from CentOS 6 but fails in bash 3.2.25(1) from CentOS 5:

[[ $file_contents =~ ^\[([^,]+),([^]]+)\] ]]; echo $?

• Start of string: ^
• Literal open square bracket: \[
• Capture start: (
• One or more of class of anything but comma: [^,]+
• Capture end: )
• Literal comma: ,
• Capture start: (
• One or more of class of anything but close square bracket: [^]]+
• Capture end: )
• Literal close square bracket: \]

Answer 2

You can use a regex like this:

\[\w+,\w+\]

Working demo