read

Read from stdin and store lines in shell variables.

Must be a shell built-in, since it modifies shell variables directly

Get string from user into variable a:

read a
echo "$a"

Cannot write with pipe into read because the pipe spawns a sub-shell, which cannot modify a variable in its parent shell: http://stackoverflow.com/questions/13763942/bash-why-piping-input-to-read-only-works-when-fed-into-while-read-const

a=a
echo b | read a   `read a` is executed in a subshell!
[ $a = a ] || exit 1

Creating a subshell does work however:

echo 'abc' | ( read b; [ "$b" = 'abc' ] || exit 1 ) || echo fail

Redirection however does work:

read a < <(printf 'abc')
[ "$a" = 'abc' ] || exit 1

This is why while combos also work:

while read l; do
  echo "$l"
done < <( printf "a\nb\na b\n" )

Read from file descriptor line-wise and assign to variable.

Applications

Read file line-by-line:

while read l; do
echo "$l";
done < "$f"

Read stdout line-by-line:

while read l; do
    echo "$l"
done < <( echo -e "a\nb\na b" )

Split into fields:

IFS_OLD="$IFS"
while IFS=' : ' read f1 f2
do
echo "$f1 $f2"
done < <( echo -e "a : b\nc : d" )
IFS="$IFS_OLD"

-p print a prompt message:

read -p 'Enter string: ' s
echo "You entered: $s"