The blocks marked Run on this page can run in your browser: the first one downloads and starts a small machine, with no network. That needs JavaScript. Without it you read the output saved with the document.

No network

Files and permissions#

Create files, change who can do what with them, find them again and read them back. Every block uses full paths, so you can run any block on its own, but the later blocks expect the files made by the first one.

Make a small tree#

sh#make

rm -rf /tmp/demo
mkdir -p /tmp/demo/notes /tmp/demo/bin
printf 'hello from wmn\n' > /tmp/demo/hello.txt
printf 'one\ntwo\nthree\n' > /tmp/demo/notes/list.txt
printf '#!/bin/sh\necho "the script ran"\n' > /tmp/demo/bin/run.sh
ls -lR /tmp/demo

New files are not executable. Look at the first column of ls -l: the letters are read, write and execute for the owner, the group and everyone else.

Read a file#

sh#read

cat /tmp/demo/hello.txt
echo "--- a longer one"
cat /tmp/demo/notes/list.txt
echo "--- a system file"
cat /etc/os-release

Change modes#

sh#chmod

/tmp/demo/bin/run.sh || echo "not allowed yet (exit $?)"
chmod u+x /tmp/demo/bin/run.sh
/tmp/demo/bin/run.sh
chmod 600 /tmp/demo/hello.txt
chmod 755 /tmp/demo/notes
stat -c '%a %A %n' /tmp/demo/hello.txt /tmp/demo/notes /tmp/demo/bin/run.sh

A mode can be symbolic (u+x: add execute for the owner) or octal (600: read and write for the owner only). In octal each digit adds read (4), write (2) and execute (1) for owner, group and others.

Find files#

sh#find

echo "text files:"
find /tmp/demo -type f -name '*.txt'
echo "executable files:"
find /tmp/demo -type f -perm -u+x
echo "directories:"
find /tmp/demo -type d

Count and compare#

sh#count

wc -l /tmp/demo/notes/list.txt
du -sk /tmp/demo
cp /tmp/demo/notes/list.txt /tmp/demo/notes/copy.txt
cmp /tmp/demo/notes/list.txt /tmp/demo/notes/copy.txt && echo "identical"

Clean up#

sh#cleanup

rm -rf /tmp/demo
ls /tmp