1st issue

As others have said, echo "$array" only prints the first element of the array; I suggest

printf '%s\n' "${array[@]}"

to print each element on a line.

2nd issue

More importantly, the loop is partially incorrect. Consider this file:

pear yellow
   apple \\ red   
orange brown    

^{Look closely: Lines 2 and 3 contain trailing spaces.}

That's what the array gets (using underscores as delimiters to better see exactly what each element contains):

$ printf '_%s_\n' "${array[@]}"
_pear yellow_
_apple \ red_
_orange brown_

1. All the leading and trailing spaces were mangled. Address that with an empty IFS.
2. \\ became \. The read command interprets backslash sequences, add the -r flag to disable that.

Solution

while IFS= read -r line; do
    array+=( "$line" )
done < file

or, better, as suggested by r~~, use mapfile -t array < file (mapfile and readarray are synonyms). It is a single command and thus more efficient.

Caveat

Finally, mind that shell loops are very slow. A test on a 10 MB file:

$ wc < /var/log/kern.log.0
  117555  1389245 10000045

~$ time { mapfile -t a < /var/log/kern.log.0; }
real    0m0.060s
user    0m0.052s
sys     0m0.008s

$ time { while IFS= read -r line; do b+=("$line"); done < /var/log/kern.log.0; }
real    0m0.720s
user    0m0.652s
sys     0m0.068s

And that is just reading the file into an array and doing nothing with it.

If attempting to process text, use actual text-processing tools (Awk, Sed, Jq, Csvkit, etc. depending on the task).

Further reading

• BashFAQ/001: How can I read a file (data stream, variable) line-by-line (and/or field-by-field)?
• Unix SE: Why is using a shell loop to process text considered bad practice?
• Unix SE: Why is while IFS= read used so often, instead of IFS=; while read?

posted over 2 years ago

CC BY-SA 4.0

Quasímodo‭

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