Inserting text to existing text within brackets

Solution 1:

A few things:

• * in regex is a quantifier; if you want behavior similar to the shell wildcard you need .* (any single character, zero or more times)

• .* matches greedily, so if you want to exclude things like = as well as the closing ] you need to do so explicitly - that's where you need non-literal [ and ]

• m does not need to be escaped on either the LHS (regex pattern) or RHS (replacement)

• you need a capture group if you want to re-use (aka backreference) the text between the brackets

• you don't need g unless you have multiple matches per line

So

$ sed -r 's|\[([^=[]*)\]|[/mame/\1]|' file
[/mame/one]

[/mame/two]

[/mame/three]

[four = something]

With Perl (which also has a -i in-place mode), you could use lookarounds and lazy (non-greedy) matching:

$ perl -pe 's{(?<=\[)([^=]*?)(?=])}{/mame/$1}' file
[/mame/one]

[/mame/two]

[/mame/three]

[four = something]

Solution 2:

I propose this:

sed '/=/!s;^\[;[/mame/;' file

Output:

[/mame/one]
[/mame/two]
[/mame/three]
[four = something]