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Q&A How to read lines into an array in Bash

Your code is correct. You have declared your variable as an array, and you are successfully appending to it. To display all of the elements of your variable, try echo "${my_array[@]}". (Another an...

posted 3y ago by r~~‭  ·  edited 3y ago by r~~‭

Answer
#4: Post edited by user avatar r~~‭ · 2021-03-22T20:22:05Z (over 3 years ago)
  • Your code is correct; another answer suggests switching to `declare -p my_array`, but this is not necessary or useful (all it does is print the attributes of the variable, which implicitly means that `my_array` defaults to being a normal string variable—the same effect is achieved by omitting the `declare` altogether). You have declared your variable as an array, and you are successfully appending to it.
  • To display all of the elements of your variable, try `echo "${my_array[@]}"`.
  • To display the current number of elements in your variable, try `echo "${#my_array[@]}"`.
  • To display the third element in the array, try `echo "${my_array[2]}"` (arrays in Bash are zero-indexed).
  • `echo $my_array` will only display the first element of the array, for what I presume are historical reasons, but that's the documented behavior. I would avoid using this ‘feature’ with array variables; it only leads to confusion.
  • ---
  • Note also that in Bash versions >= 4, the `readarray` builtin will do all of this work for you:
  • `readarray -t my_array < my_file.txt`
  • You don't even need to declare `my_array` beforehand if you use this builtin. Bash 4 was released in 2009, so unless you're working on a pretty old or stripped-down system, you are probably safe using that.
  • Your code is correct. You have declared your variable as an array, and you are successfully appending to it.
  • To display all of the elements of your variable, try `echo "${my_array[@]}"`. (Another answer suggests `declare -p` for this, but `declare -p` will possibly give you more information than you wanted. Also, be aware that `declare -p` isn't intended to *substitute* for your `declare -a`; it's an additional command to show the status of your variable.)
  • To display the current number of elements in your variable, try `echo "${#my_array[@]}"`.
  • To display the third element in the array, try `echo "${my_array[2]}"` (arrays in Bash are zero-indexed).
  • `echo $my_array` will only display the first element of the array, for what I presume are historical reasons, but that's the documented behavior. I would avoid using this ‘feature’ with array variables; it only leads to confusion.
  • ---
  • Note also that in Bash versions >= 4, the `readarray` builtin will do all of this work for you:
  • `readarray -t my_array < my_file.txt`
  • You don't even need to declare `my_array` beforehand if you use this builtin. Bash 4 was released in 2009, so unless you're working on a pretty old or stripped-down system, you are probably safe using that.
#3: Post edited by user avatar r~~‭ · 2021-03-22T20:17:59Z (over 3 years ago)
  • Your code is correct; another answer suggests switching to `declare -p my_array`, but this is not necessary or useful (all it does is print the attributes of the variable, which implicitly means that `my_array` defaults to being a normal string variable—the same effect is achieved by omitting the `declare` altogether). You have declared your variable as an array, and you are successfully appending to it.
  • To display all of the elements of your variable, try `echo "${my_array[@]}"`.
  • To display the current number of elements in your variable, try `echo "${#my_array[@]}"`.
  • To display the third element in the array, try `echo "${my_array[2]}"` (arrays in Bash are zero-indexed).
  • `echo $my_array` will only display the first element of the array, for what I presume are historical reasons, but that's the documented behavior. I would avoid using this ‘feature’ with array variables; it only leads to confusion.
  • Your code is correct; another answer suggests switching to `declare -p my_array`, but this is not necessary or useful (all it does is print the attributes of the variable, which implicitly means that `my_array` defaults to being a normal string variable—the same effect is achieved by omitting the `declare` altogether). You have declared your variable as an array, and you are successfully appending to it.
  • To display all of the elements of your variable, try `echo "${my_array[@]}"`.
  • To display the current number of elements in your variable, try `echo "${#my_array[@]}"`.
  • To display the third element in the array, try `echo "${my_array[2]}"` (arrays in Bash are zero-indexed).
  • `echo $my_array` will only display the first element of the array, for what I presume are historical reasons, but that's the documented behavior. I would avoid using this ‘feature’ with array variables; it only leads to confusion.
  • ---
  • Note also that in Bash versions >= 4, the `readarray` builtin will do all of this work for you:
  • `readarray -t my_array < my_file.txt`
  • You don't even need to declare `my_array` beforehand if you use this builtin. Bash 4 was released in 2009, so unless you're working on a pretty old or stripped-down system, you are probably safe using that.
#2: Post edited by user avatar r~~‭ · 2021-03-22T20:10:20Z (over 3 years ago)
  • Your code is correct; another answer suggests switching to `declare -p my_array`, but this is not necessary or useful (all it does is print the attributes of the variable, which implicitly means that `my_array` defaults to being a normal string variable—the same effect is achieved by omitting the `declare` altogether). You have declared your variable as an array type, and you are successfully appending to it.
  • To display all of the elements of your variable, try `echo "${my_array[@]}"`.
  • To display the current number of elements in your variable, try `echo "${#my_array[@]}"`.
  • To display the third element in the array, try `echo "${my_array[2]}"` (arrays in Bash are zero-indexed).
  • `echo $my_array` will only display the first element of the array, for what I presume are historical reasons, but that's the documented behavior. I would avoid using this ‘feature’ with array variables; it only leads to confusion.
  • Your code is correct; another answer suggests switching to `declare -p my_array`, but this is not necessary or useful (all it does is print the attributes of the variable, which implicitly means that `my_array` defaults to being a normal string variable—the same effect is achieved by omitting the `declare` altogether). You have declared your variable as an array, and you are successfully appending to it.
  • To display all of the elements of your variable, try `echo "${my_array[@]}"`.
  • To display the current number of elements in your variable, try `echo "${#my_array[@]}"`.
  • To display the third element in the array, try `echo "${my_array[2]}"` (arrays in Bash are zero-indexed).
  • `echo $my_array` will only display the first element of the array, for what I presume are historical reasons, but that's the documented behavior. I would avoid using this ‘feature’ with array variables; it only leads to confusion.
#1: Initial revision by user avatar r~~‭ · 2021-03-22T20:07:28Z (over 3 years ago)
Your code is correct; another answer suggests switching to `declare -p my_array`, but this is not necessary or useful (all it does is print the attributes of the variable, which implicitly means that `my_array` defaults to being a normal string variable—the same effect is achieved by omitting the `declare` altogether). You have declared your variable as an array type, and you are successfully appending to it.

To display all of the elements of your variable, try `echo "${my_array[@]}"`.

To display the current number of elements in your variable, try `echo "${#my_array[@]}"`.

To display the third element in the array, try `echo "${my_array[2]}"` (arrays in Bash are zero-indexed).

`echo $my_array` will only display the first element of the array, for what I presume are historical reasons, but that's the documented behavior. I would avoid using this ‘feature’ with array variables; it only leads to confusion.