bash - output each array element on new line

Question

I am trying to create a TSV file from an array that I build inside a loop. I do get the values on each line to be tab separated, but I am not able to export each element of the array on a new line. This is an example:

OUTPUT=()
#header
OUTPUT+=$(printf "col_1\tcol_2\tcol_3")

param_1="bla"
param_2="tra"
param_3="meh"

for i in 1 .. 3
  do
    OUTPUT+=$(printf "$param_1\t$param_2\t$param_3")
done
#export
printf '%s\n' "${OUTPUT[@]}" > test.tsv

I have also tried to put \n at the end of each string that I insert in the array, but it did not work. Any idea what I am doing wrong? Thank you

if it's going to end up in a file, there is no need to have the intermediate array layer, you can directly write the elements to the file. If you don't want the in-the-flight file to be visible, you can use a temp file and move to final name at the end. — karakfa
– karakfa, Commented Feb 17, 2017 at 15:26
yes, if you intend to use scripting in the future, this is not the way to be writing to files (although, yes, you can). Better to spend your time learning a tool designed for manipulating data (and reading/writing to files). Check out awk tutorial or if you need unlimited control and system features, OO, etc etc, find a python or perl tutorial that works for you. Good luck. — shellter
– shellter, Commented Feb 17, 2017 at 15:30
@karakfa I would avoid using a temp file and write at every iteration in it... why bother.. even if it is buffered and my output will not exceed half an MB. I can very well output only once at the end, no? — Marius
– Marius, Commented Feb 17, 2017 at 15:39
@shellter thanks for your comment. For this simple example I have no need to use awk or other dedicated tools. If I need to get something more complex done, then of course I would use something more appropriate. I just needed to write a script to be in line with the other existing scripts and not use a different programming language/tool just for a simple task — Marius
– Marius, Commented Feb 17, 2017 at 15:42
the reason is not exposing in-the-flight file to other processes prematurely. It's an integrity issue rather then performance. However, may not be necessary in your particular case. — karakfa
– karakfa, Commented Feb 17, 2017 at 15:43

anubhava · Accepted Answer · 2017-02-17 15:22:31Z

3

To append to an array you should use this syntax:

array+=(content)

Also there is no need to use printf for appending the static text.

Here is a working script:

OUTPUT=()
#header
OUTPUT+=("col_1\tcol_2\tcol_3")

param_1="bla"
param_2="tra"
param_3="meh"

for i in {1..3}
do
    OUTPUT+=("$param_1\t$param_2\t$param_3")
done
#export
printf '%b\n' "${OUTPUT[@]}" > test.tsv

Note use of %b in printf so that escape sequences are interpreted correctly.

Output:

cat test.tsv

col_1   col_2   col_3
bla     tra     meh
bla     tra     meh
bla     tra     meh

answered Feb 17, 2017 at 15:22

anubhava

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1 Comment

Marius Over a year ago

Hi. Thanks for the answer. It works now. So, the thing that actually makes a difference is the conversion to binary, %b in the printf exporting to file which will expand all escape characters. I have tried before without using printf while adding elements to the array but it would print all the string with \t. Thanks once again

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