Read a file (data stream, variable) line-by-line (and/or field-by-field)?

Parameters#

Parameter	Details
IFS	Internal field separator
file	A file name/path
`-r`	Prevents backslash interpretation when used with read
`-t`	Removes a trailing newline from each line read by `readarray`
`-d DELIM`	Continue until the first character of DELIM is read (with `read`), rather than newline
## Reads file (/etc/passwd) line by line and field by field

readarray -t arr <file

Or with a loop:

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

while IFS= read -r line; do
   echo "$line"
done <file

If file may not include a newline at the end, then:

while IFS= read -r line || [ -n "$line" ]; do
   echo "$line"
done <file

var='line 1
line 2
line3'
readarray -t arr <<< "$var"

or with a loop:

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

var='line 1
line 2
line3'
while IFS= read -r line; do
   echo "-$line-"
done <<< "$var"

readarray -t arr <<< "$var"
for i in "${arr[@]}";do
    echo "-$i-"
done

while IFS= read -r line;do
    echo "**$line**"
done < <(ping google.com)

or with a pipe:

ping google.com |
while IFS= read -r line;do
    echo "**$line**"
done

Let’s assume that the field separator is : (colon) in the file file.

while IFS= read -d : -r field || [ -n "$field" ]; do
   echo "$field"
done <file

For a content:

first : se
con
d:
    Thi rd:
    Fourth

The output is:

**first **
** se
con
d**
**
    Thi rd**
**
    Fourth
**

Let’s assume that the field separator is :

var='line: 1
line: 2
line3'
while IFS= read -d : -r field || [ -n "$field" ]; do
   echo "-$field-"
done <<< "$var"

Output:

-line-
- 1
line-
- 2
line3
-

Let’s assume that the field separator is :

arr=()
while IFS= read -d : -r field || [ -n "$field" ]; do
   arr+=("$field")
done <file

Let’s assume that the field separator is :

var='1:2:3:4:
newline'
arr=()
while IFS= read -d : -r field || [ -n "$field" ]; do
   arr+=("$field")
done <<< "$var"
echo "${arr[4]}"

Output:

newline

Let’s assume that the field separator is :

while IFS= read -d : -r field || [ -n "$field" ];do
    echo "**$field**"
done < <(ping google.com)

Or with a pipe:

ping google.com | while IFS= read -d : -r field || [ -n "$field" ];do
    echo "**$field**"
done