I have an array in Bash, each element is a string. How can I append another string to each element? In Java, the code is something like:
for (int i=0; i<array.length; i++)
{
array[i].append("content");
}
4 Answers
As mentioned by hal
array=( "${array[@]/%/_content}" )
will append the '_content' string to each element.
array=( "${array[@]/#/prefix_}" )
will prepend 'prefix_' string to each element
7 Comments
the
Thanks. I was actually looking for prepending a string, so your
# addition is very useful to me.
starfry
This, succinct and to the point, should be the accepted answer. It works with any string manipulation and applies the manipulation to each array element.
roachsinai
How about append the '_content' string to each dictionary keys?
ZFY
what if prepend and append same time? /%/_content/#/prefix seems doesn't work.
sorpigal
@ZFY: you would need to perform two passes.
|
You can append a string to every array item even without looping in Bash!
# cf. http://codesnippets.joyent.com/posts/show/1826
array=(a b c d e)
array=( "${array[@]/%/_content}" )
printf '%s\n' "${array[@]}"
4 Comments
Rajish
Good one! Is not the exact answer to the question, but is the unquestionable winner of the do-it-shorter competition! +1
Felix Rabe
The Joyent link is broken, see web.archive.org/web/20101114051536/http://… instead (Wayback Machine for that link).
Chris Down
Note: this does actually loop internally.
Magne
NB: If you have IFS=$'\n' (to handle names with whitespace) then the append command will not keep the original array structure. It will just make array contain only 1 item (a string list), with all the changed strings. As seen if you run:
declare -p array afterwards.Tested, and it works:
array=(a b c d e)
cnt=${#array[@]}
for ((i=0;i<cnt;i++)); do
array[i]="${array[i]}$i"
echo "${array[i]}"
done
produces:
a0
b1
c2
d3
e4
EDIT: declaration of the array could be shortened to
array=({a..e})
To help you understand arrays and their syntax in bash the reference is a good start. Also I recommend you bash-hackers explanation.
5 Comments
Richard
it works... but a bit confusing. can u explain what does "{}" mean, as in ${array[i]}? why not $array[$i]?
sehe
@Richard: unfortunately, the syntax required to work with bash arrays is ... arcane to put it mildly; I don't believe it can be explained easier than the man-page for bash does it. (Moreover, this serves as the 'stay-away sign' for me)
Gordon Davisson
array[i]="${array[i]}$i" can be simplified to: array[$i]+="$i"
Liso
Thanks, this gives me idea to append string to specific element +1
mirekphd
...and this is the one that works for prefixes (prepending a string before the array elements), not just suffixes
You pass in the length of the array as the index for the assignment. The length is 1-based and the array is 0-based indexed, so by passing the length in you are telling bash to assign your value to the slot after the last one in the array. To get the length of an array, your use this ${array[@]} syntax.
declare -a array
array[${#array[@]}]=1
array[${#array[@]}]=2
array[${#array[@]}]=3
array[${#array[@]}]=4
array[${#array[@]}]=5
echo ${array[@]}
Produces
1 2 3 4 5
3 Comments
sehe
good answer. regrettably the required syntax (sin tax) can not be sufficiently lamented
Steve Prentice
Just reread the question and realized I answered something slightly different. I'll leave this answer here though since it still has some valuable information regarding arrays in bash.
Peter.O
array+=(1); array+=(2); ... array+=(etc)
cannot find symbol symbol : method append(java.lang.String) location: class java.lang.String array[i].append (" content");The simplified for-loop should slowly - after 5 years - be adopted too.for (String s: array) System.out.println (s + " content");