Extract string from brackets

Question

I'm pretty new at bash so this is a pretty noob question..

Suppose I have a string:

string1 [string2] string3 string4 

I would like to extract string2 from the square brackets; but the brackets may be surrounding any other string at any other time.

How would I use sed, etc, to do this? Thanks!

Answer 1

Try this:

echo $str | cut -d "[" -f2 | cut -d "]" -f1 

Answer 2

Here's one way using awk:

echo "string1 [string2] string3 string4" | awk -F'[][]' '{print $2}' 

This sed option also works:

echo "string1 [string2] string3 string4" | sed 's/.*\[\([^]]*\)\].*/\1/g' 

Here's a breakdown of the sed command:

s/          <-- this means it should perform a substitution .*          <-- this means match zero or more characters \[          <-- this means match a literal [ character \(          <-- this starts saving the pattern for later use [^]]*       <-- this means match any character that is not a [ character                 the outer [ and ] signify that this is a character class                 having the ^ character as the first character in the class means "not" \)          <-- this closes the saving of the pattern match for later use \]          <-- this means match a literal ] character .*          <-- this means match zero or more characters /\1         <-- this means replace everything matched with the first saved pattern                 (the match between "\(" and "\)" ) /g          <-- this means the substitution is global (all occurrences on the line)