Cabin Guest Book

Putting text in a file and getting it back

The > after a command sends its output into a file instead of the screen. If the file exists, > empties it first and then writes — every time. To add to the end instead, use >>. So a script that builds a list line by line starts with one > and continues with >>.

Files here live in a small in-memory filesystem that exists only for the length of the run, so you can write freely; nothing on your computer is touched.

cat prints a file. wc -l counts its lines, and wc -l < file prints just the number, with no filename after it — the < hands the file to wc as its input.

The same < is how a loop reads a file one line at a time:

while read -r line; do
  echo "- $line"
done < list.txt

read takes one line and puts it in the variable; when the file runs out, read fails and the loop stops. The -r tells read to keep backslashes as they are. The < list.txt goes after done, because it feeds the whole loop, not just one command inside it.

A worked example

echo "Bring a torch" > list.txt
echo "Bring a map" >> list.txt
echo "Lines: $(wc -l < list.txt)"
while read -r line; do
  echo "- $line"
done < list.txt

Lines: 2
- Bring a torch
- Bring a map

The first echo creates the file, the second appends, and the loop reads both lines back.

Your turn

The editor holds a guest book for a cabin. Three names are written to guests.txt, then the script prints the book, counts the guests, and prints a welcome line for each.

Two lines are marked. The second name is written with > instead of >>, so it wipes out the first name — the book ends up with two guests instead of three. The loop's done line is missing the <, so a bare word right after done is a syntax error, and the script stops before the loop can print a single welcome line.

Fix both. You should see all three names in the book, a count of 3, and three welcome lines.

If something goes wrong

If the first guest is missing from the book, one of the echo lines is still using >. Only the very first write should use >.

A syntax error pointing at guests.txt means the redirect after done is still missing its <.

If the loop prints nothing, check the < is after done, not somewhere inside the loop body.