Extracting the second word from a string variable

Question

I have a string "rtcpOnNbActive true" stored in a variable x. I want to extract "true" as substring and store in a variable. How can I do this?

Solution 1

Try this way:

y=$(echo $x | awk '{print $2}')
echo $y

• echo $x display the value of x.
• awk '{print $2}' prints the second field of the previously displayed x.
• $(...) hold the output and let assign it to y.

Solution 2

Assuming that there's at least one space before the substring you wish to extract (and that the substring does not contain any spaces), you can do this with a simple parameter expansion:

x="rtcpOnNbActive     true"
y="${x##* }"
echo "[$y]"

output

[true]

Solution 3

It's possible to use bash arrays for that, just place your str inside parenthesis. e.g.:

arr=("first second third")
echo ${arr[1]}

str="first second third"
arr1=($str)
echo ${arr1[1]}

Solution 4

you can use awk:

echo "rtcpOnNbActive         true" | awk '{print $NF}'
true

NF number of field in the current record

using sed:

echo "rtcpOnNbActive         true" | sed 's/.* //g'
true

using string expression:

 a="rtcpOnNbActive         true"
 echo ${a##* }
 true

using grep:

 echo "rtcpOnNbActive         true" | grep -Eo "[a-z]+$"
 true

-o is gives only exact match, [a-z]+ will match letter from a-z and $ means at end

Solution 5

You could use the read built-in

read -r _ y <<<"$x"
printf "%s\n" "$y"
true

View more solutions

Comments

[PM 2Ring]

Will there always be a space in x just before the substring you want to extract?

[Stéphane Chazelas]

echo $x is not display the value of x. printf '%s\n' "$x" would be.

[Stéphane Chazelas]

awk '{print $2}' prints the second field of each line of the previously displayed x.

[αғsнιη]

Don't post content of other answer for yours in the same question, please.

[nyuszika7h]

echo is not portable for anything other than a literal string that doesn't start with - and doesn't contain any escape sequences. Its behavior varies even for the bash builtin, depending on how it was compiled, and whether XPG_ECHO is set. Assuming the string contains no escape sequences, this should be fine, but printf '[%s]\n' "$y" is still better.

[nyuszika7h]

echo is not portable for anything other than a literal string that doesn't start with - and doesn't contain any escape sequences. Its behavior varies even for the bash builtin, depending on how it was compiled, and whether XPG_ECHO is set. Also, you should always double quote variable expansions and command substitution (with certain exceptions, where it's not necessary but it doesn't do any harm either). With a string like the OP's, this should be fine, but if you want to make sure printf '%s\n' "${a##* }" would be better.

[mikeserv]

why involve read? It isn't read that does the split - it is $IFS. For some reason a lot of people consider it ok to split w/ $IFS only when read is involved. You can just do: set -f; IFS=' '; printf %.0s%s $x or whatever. In any case - you need to specify $IFS's value here.

[Mathias Begert]

@mikeserv, it's read doing the splitting using IFS, check the documentation. The main advantage with using read is that it sets variables (which is an OP requirement) and given that it can split strings and populate an array, is good for extracting arbitrary fields from a string. Additionally, I am assuming default IFS here, but it's easy enough to set if needed, IFS=$' \n\t' read -r _ y <<<"$x" will do the trick

[Mathias Begert]

@mikeserv, you're off my Christmas card list.

[PM 2Ring]

@nyuszika7h: Good point, and after having read Stéphane Chazelas say similar things here and in other recent questions I really ought to break my habit of using echo to display the value of variables, even in "throw-away" examples like this.

[mikeserv]

bah humbug. xmas is for suckers.

[prashant thakre]

This is the best approach thanks its very simple and not an errorpron.

[Cecil Curry]

The only sane solution. Every other solution either invokes external third-party commands that may not necessarily be available or behave as expected under the current platform (e.g., awk) or performs fragile string-munging guaranteed to fail in obvious corner cases (e.g., echo "${x##* }").