POSIX Shell and Coreutils

POSIX Shell & Coreutils Reference

@innovatorved/code-lab includes a pure-JavaScript POSIX shell AST interpreter and 40+ UNIX coreutils running directly against the in-memory Virtual Filesystem (VFS).

It requires zero eval(), zero new Function(), and is 100% Content Security Policy (CSP) compliant.

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1. Shell Syntax & Operators

Pipelines (|)

Chain stdout of one command directly into stdin of the next:

cat balancer.js | grep -n "class" | head -n 5
find . -name "*.js" | wc -l
cat access.log | grep " 500 " | awk '{print $1}' | sort | uniq -c

Redirection (>, >>, <, 2>&1, &>)

Redirect command output to or from virtual files:

# Overwrite file
echo "hello world" > out.txt

# Append to file
echo "another line" >> out.txt

# Redirect stderr to stdout
node broken.js > log.txt 2>&1

# Redirect all streams
cmd &> combined.log

# Input redirection
wc -l < data.json

Logical Chaining (&&, ||, ;)

# Execute sequentially regardless of exit code
mkdir src; touch src/index.ts; ls -la src

# Execute only if preceding command succeeded (exit code 0)
node demo.js > demo.log && cat demo.log

# Fallback on failure
grep -q "TODO" solution.js || echo "All TODOs completed!"

Background Execution (&) & Process Table

Keep long-running servers or jobs listening in the background:

# Start an HTTP server in the background
node server.js &
# or
bun run server.ts &

# View active processes and port bindings
ps
ports

# Terminate process by PID
kill 1

Environment Variables & Command Substitution

# Set and export variable
export PORT=8080
echo "Listening on $PORT"

# Default value syntax
echo "User: ${NAME:-anonymous}"

# Last exit code
echo $?

# Command substitution
echo "Current directory contains $(ls | wc -l) files"

Glob Expansion

Wildcards match filenames directly against the virtual filesystem:

ls *.js
rm -f src/**/*.bak
head -n 2 test/*.js

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2. Supported Coreutils Reference (40+ Commands)

Command	Supported Flags	Description	Example
ls	-l, -a, -la, -1, -h	List directory contents	ls -la /workspace
cd	(path)	Change working directory	cd src/
pwd	none	Print current working directory	pwd
cat	-n, -b	Concatenate files to stdout	cat balancer.js
head	-n <num>	Output first N lines of file/stdin	head -n 10 demo.js
tail	-n <num>	Output last N lines of file/stdin	tail -n 5 out.log
grep	-n, -i, -r, -v, -E	Search patterns in text or files	grep -rin "export" .
find	-name, -type [f/d], -maxdepth	Find files matching pattern	find src/ -name "*.ts"
wc	-l (lines), -w (words), -c (bytes)	Print newline, word, and byte counts	wc -l README.md
sort	-r (reverse), -n (numeric), -u (unique)	Sort lines of text files	sort -n numbers.txt
uniq	-c (count), -i (case-insensitive)	Report or omit repeated lines	sort file | uniq -c
sed	s/find/replace/g, d	Stream editor for filtering and transforming text	sed 's/foo/bar/g' in.txt
awk	-F <delim>, '{print $N}'	Pattern scanning and processing	awk -F: '{print $1}' /etc/passwd
cut	-d <delim>, -f <field>, -c <chars>	Remove sections from lines	cut -d, -f2 data.csv
tr	-d, set1 set2	Translate or delete characters	echo "abc" | tr 'a-z' 'A-Z'
diff	-u	Compare files line by line	diff -u starter.js solution.js
tree	-L <depth>, -a	List contents of directories in a tree format	tree -L 2
cp	-r (recursive), -f	Copy files and directories	cp -r src/ src-backup/
mv	-f	Move or rename files	mv demo.js demo.old.js
rm	-r (recursive), -f (force)	Remove files or directories	rm -rf dist/
mkdir	-p (parents)	Make directories	mkdir -p src/lib/
touch	none	Update timestamps or create empty files	touch server.ts
stat	none	Display file or file system status	stat README.md
chmod	none	Change file mode bits	chmod +x script.sh
echo	-n, -e	Display a line of text	echo "hello"
printf	format specifiers (%s, %d, etc.)	Format and print data	printf "val=%d\n" 42
curl	-i, -v, -s, -X, -H, -d	Transfer data from or to an HTTP server	curl -i http://localhost:3000
node	<file>, -e, -p, --test	Run Node.js scripts or start interactive REPL	node demo.js
bun	run <file>, test, init, repl	Run Bun scripts or test suites natively	bun run server.ts &
npm	install <pkg>, test, run <script>	Manage packages and run scripts	bun add zod
git	status, diff, log, branch	In-memory Git status and history	git status
ps	none	Report snapshot of current processes	ps
ports	none	List active listening TCP / HTTP ports	ports
jobs	none	List background jobs	jobs
kill	<pid>	Terminate process by PID	kill 1
clear	none	Clear the terminal screen	clear
history	none	Display previously executed commands	history
date	none	Display current time and date	date
sleep	<seconds>	Delay for a specified amount of time	sleep 2
whoami	none	Print current effective userid	whoami
uname	-a	Print system information	uname -a
which	<command>	Locate a command	which node
env	none	Print environment variables	env
export	KEY=val	Set export attribute for shell variables	export NODE_ENV=production
unset	KEY	Unset values and attributes of variables	unset NODE_ENV
help	none	Display summary of built-in commands	help