Reading file with "cat" and creating array

SafetyMark · 10-21-2016, 10:43 AM

Hi,

I'm beginner at bash so I decided to ask you about my problem.

I was trying to sort some numbers which are stored in text. I want to read file using cat and than store it to array so I can sort those numbers by using bubble sort (I know there is sort already implemented in bash, but I prefer bubble sort).

I was trying something like this

Code:

input=$1
myText=`cat $1`
myArray=${#myText[*]}
#I was trying also
#myArray=( $(cat "$1") )

When I try to echo $myText its working, but when using bubble sort it is not working.

Thanks for your help.

HMW · 10-21-2016, 11:10 AM

$1 is the first argument passed to a program in bash, I don't really understand the usage here.

If you want to read from a file into an array, you can do something like this:

Code:

HMW@debian-HP:~/Slask$ echo "foo bar baz" >> myFile
HMW@debian-HP:~/Slask$ myarr=($(cat myFile))
HMW@debian-HP:~/Slask$ echo ${myarr[@]} 
foo bar baz

SafetyMark · 10-21-2016, 11:39 AM

Yes in $1 is stored "argument" which I pass to program. For example

Code:

bash myscript.sh myfile.txt

. I'm using it inside if so I can check if user passed file to script or not.

Text file is already saved on Desktop because I'm trying project everytime on the same file (to check if it is working).

ondoho · 10-21-2016, 12:20 PM

what output do you get for

Code:

echo "$MyArray"

???

SafetyMark · 10-21-2016, 12:38 PM

If I write

Code:

echo "$myText" 
I got
5 1 2 3 4

but If I write

Code:

echo "$myArray"
I got
1

grail · 10-21-2016, 12:46 PM

Without () around your data you will never create an array in bash, unless you individually assign each value to a specific index.

So let us look at what you have done:

input=$1 :- here you assign the value of the first parameter to a variable. Great idea except then you never use the variable

myText=`cat $1` :- here you assign the contents of the file passed as first parameter to a variable. Note I said contents, hence the variable contains the entire file, newlines and all.

myArray=${#myText[*]} :- here you assign the length of an "array" to a variable. I quoted "array" as in fact it is only a string but bash will let you refer to it in the same way, however, here it will
return the value 1 as by definition there is only 1 index value (this being the zero'th value) which has all of your data stored in it.

If you want more proof that you have not created an array, try the following:

Code:

echo ${#myText[0]}

You will find the output to not be at all what you expected.

As shown by HMW, your commented out version, #myArray=( $(cat "$1") ), was actually the correct way to create an array.
My own preference would be (although the exact same outcome):

Code:

input="$1"

my_array=($(< "$input"))

szboardstretcher · 10-21-2016, 12:49 PM

Quote:

I want to read file using cat and than store it to array so I can sort those numbers

This is as small as i could make it (using redirection instead of cat):

Code:

shuf -i 1-999 -n 20 > numbers
mapfile -t unsorted < numbers
declare -p unsorted > /dev/null 2>&1
IFS=$'\n' sorted=($(sort -n <<< "${unsorted[*]}"))
printf "%s\n" "${sorted[@]}"

SafetyMark · 10-21-2016, 01:16 PM

So I guess is easier to use other ways to solve this problem than use "cat"?

I'm still curious how would the cat version look like.

szboardstretcher · 10-21-2016, 01:25 PM

using cat?

Code:

shuf -i 1-999 -n 20 > numbers
cat numbers | mapfile -t unsorted
declare -p unsorted > /dev/null 2>&1
IFS=$'\n' sorted=($(sort -n <<< "${unsorted[*]}"))
printf "%s\n" "${sorted[@]}"

Not sure if this is what you meant.

linux.bash255 · 11-11-2016, 09:49 AM

Try:

Quote:

IFS=$'\n'
arr=(`cat $1`)
echo ${arr[@]}

Few examples: masteringunixshell.net/qa36/bash-how-to-add-to-array.html