while read in Bash

The line-by-line loop that processes streams.

# while read consumes input line by line; IFS= keeps leading spaces
printf 'alpha\n  beta\ngamma\n' | while IFS= read -r line; do
    echo "got: [$line]"
done

# a counter loop with a condition
n=1
while (( n < 30 )); do
    n=$(( n * 3 ))
done
echo "stopped at $n"

How it works

IFS= read -r reads one raw line, spaces and all.
The pipe feeds the loop; each iteration gets one line.
(( )) conditions drive counter loops the same way.

Keywords and builtins used here

do
done
echo
printf
read
while

The run, in numbers

Lines: 11
Characters to type: 257
Tokens: 46
Three-star pace: 80 tpm

At the three-star pace of 80 tokens a minute, this run takes about 34 seconds.

Type this snippet

Step 2 of 3 in Loops, step 8 of 26 in Language basics.

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