Splitting string with a while command

Question

I can not find a way to correctly split a simple input string by a configurable separator

Script:

#!/bin/bash
while IFS='|' read -r name; do
  echo "$name";
done <<< "one|two|three"

Actual output :

one|two|three

Expected output:

one
two
three

I'm using `GNU bash, version 4.4.20(1)-release (x86_64-redhat-linux-gnu)`

Answer 1

IFS='|' read -r name will split the input using | as the delimiter but then you only give it one variable (name) in which to store the 3 components. Consider the following:

$ IFS='|' read -r var1 <<< "one|two|three"
$ typeset -p var1
declare -- var1="one|two|three"                    # "one" plus leftover "two|three"

$ IFS='|' read -r var1 var2 <<< "one|two|three"
$ typeset -p var1 var2
declare -- var1="one"
declare -- var2="two|three"                        # "two" plus leftover "|three"

$ IFS='|' read -r var1 var2 var3 <<< "one|two|three"
$ typeset -p var1 var2 var3
declare -- var1="one"
declare -- var2="two"
declare -- var3="three"                            # "three" plus *no leftover*

$ IFS='|' read -r var1 var2 var3 var4 <<< "one|two|three"
$ typeset -p var1 var2 var3 var4
declare -- var1="one"
declare -- var2="two"
declare -- var3="three"
declare -- var4=""                                 # not enough delimited items to populate "var4"

In your case, assuming you know there will always be 3 items, is to provide 3 variables for read to populate, eg:

while IFS='|' read -r name1 name2 name3; do        # modify to use 3 distinct variable names as you see fit
    echo "name1:$name1:"
    echo "name2:$name2:"
    echo "name2:$name3:"
done <<< "one|two|three"

This will generate:

name1:one:
name2:two:
name2:three:

Keep in mind this solution will only loop once, with all 3 items available in said single loop.

---

If the intent is to loop 3 times, with each loop processing just 1 item, then we need to (in essence) break the input into 3 separate items - one per line.

One option would be convert the | delimiters into linefeeds (\n).

One idea using tr, eg:

$ tr '|' '\n' <<< "one|two|three"
one
two
three

Modifying your current code to utilize the tr output:

cnt=0

while read -r name; do
    ((cnt++))
    echo "loop #${cnt} : name=$name"
done < <(tr '|' '\n' <<< "one|two|three")

This generates:

loop #1 : name=one
loop #2 : name=two
loop #3 : name=three

An alternative approach would use read to split the input into array elements (See Diego's answer) and then loop through the array elements, eg:

IFS='|' read -ra names <<< "one|two|three"

cnt=0

for name in "${names[@]}"; do
    ((cnt++))
    echo "loop #${cnt} : name=$name"
done

This also generates:

loop #1 : name=one
loop #2 : name=two
loop #3 : name=three