read input from a file and append that values to variables using shell

Question

I'm trying to write a bash script to read a file as input and append the values/data in that file into variables and the values of the variables should be updated each iteration based on the input line from the file.

Eg: Input file looks like below:

100  Thomas  Manager    Sales       $5,000
200  Jason   Developer  Technology  $5,500
300  Sanjay  Sysadmin   Technology  $7,000
400  Nisha   Manager    Marketing   $9,500
500  Randy   DBA        Technology  $6,000

While reading this through my shell script, I'll define 5 variables let's a,b,c,d,e.

First iteration:

The variable values should be assigned with first line of input file.

a=100
b=Thomas
c=Manager
d=Sales
e=$5000

Second iteration:

The variable values should be assigned with second line of input file.

a=200
b=Jason
c=Developer
d=Technology
e=$5500

And so on...

Please anyone give some input on how to write a script to read values in this format.

Answer 1

You can use the read builtin command with option -a with a loop to read each line of the file as an array. Then you can assign the value of the array elements to the variables you need (or you can use the array elements directly in your script):

#!/bin/bash

IN_FILE='./in-file.txt'

while read -ra LINE
do
        a="${LINE[0]}"; b="${LINE[1]}"; c="${LINE[2]}"
        d="${LINE[3]}"; e="${LINE[4]}"

        echo -e "$a\n$b\n$c\n$d\n$e\n"

done < "$IN_FILE"

Another way is to assign the values of each column of certain line directly to the variables. The following example uses bash function that will feed the variables with new values when it is called. The function has one input parameter, that determines which line from the file to be parsed.

#!/bin/bash

IN_FILE='./in-file.txt'

args_feed() {
        read -r a b c d e <<< "$(sed "$1 q;d" "$IN_FILE")"
}

# -----------------
# Examples of usage
# -----------------

# Parse the third line
args_feed 3
echo -e "$a\n$b\n$c\n$d\n$e\n"


# Sequential call - First iteration
args_feed $((++LINE_NR))
echo -e "$a\n$b\n$c\n$d\n$e\n"

# Sequential call - Second iteration
args_feed $((++LINE_NR))
echo -e "$a\n$b\n$c\n$d\n$e\n"


# Parse the entire file
NR_LINES="$(cat "$IN_FILE" | wc -l)"
for LINE_NR in $(seq 1 $NR_LINES)
do
        args_feed "$LINE_NR"
        echo -e "$a\n$b\n$c\n$d\n$e\n"
done

Notes:

• The default value of $IFS is spaces and tabs, that is applicable in this case. For more details, please read this encyclopedic answer.

• The -r option used in the both examples, passed to read command prevents backslash escapes from being interpreted.

• According to the usage of sed, within the second example, read this answer.

• For more examples, please see the previews version of the answer.