Excursion: Shells

No program runs without context. In application programming this would usually be a "shell" - a special program that provides operating system services and environment to the user or other programs.

Shell Cheat Sheet

Subject	Linux Bash command 1	Windows Powershell command 1 2
Shell
shell version	bash --version	$PSVersionTable
list available commands	compgen -c | sort | uniq 3	get-command
command help	<command> --help	help <command>
shell command history	history	history
search shell command history	<ctrl>-r	<ctrl>-r
shell command navigation	<arrow-up> or <arrow-down>	<arrow-up> or <arrow-down>
Directories
show current working directory	pwd	pwd
change drive	NOT-AVAILABLE	C:
list directory content	ls	ls
list directory content using wildcards	ls foo*	ls foo*
list directory tree	tree -L <level>	tree
change directory	cd <directory>	cd <directory>
create directory	mkdir FOO	mkdir FOO
remove/delete directory	rmdir FOO	rmdir FOO
move (and/or rename) directory	mv FOO BAR	mv FOO BAR
Files
create file	touch foo.txt	new-item foo.txt -itemtype file
copy file	cp foo.txt bar.txt	cp foo.txt bar.txt
remove/delete file	rm bar.txt	rm bar.txt
move (and/or rename) file	mv foo.txt bar.txt	mv foo.txt bar.txt
append content to a text-file ('>>'-operator)	echo "Hello World" >> bar.txt	echo "Hello World" >> bar.txt
overwrite content of a text-file ('>'-operator)	echo "Hello World" > bar.txt	echo "Hello World" > bar.txt
show text-file content	cat bar.txt	cat bar.txt
Environment Variables
list all environment variables	env	ls env:
some predefined environment variables	USER, HOME, PATH	USERNAME, HOMEPATH, PATH
get/show environment variable	echo $<variable>	$env:<variable>
set environment variable 4	FOO=foo	$env:FOO="foo"
extend value of environment variable	FOO+=$USER	$env:FOO += $env:USERNAME
remove/delete environment variable	unset FOO	remove-item env:FOO
Shell script example
Using environment variable and calling Python	see test-env.sh in 5	see test-env.ps1 6

    # test-env.sh
    echo "USER (Output from Bash): $USER"
    /usr/bin/python3.8 -c "import os; print('USER (Output from Python provided by Bash): $USER'); print('USER (Output from Python resolved from Python): {}'.format(os.environ['USER']))"

    # test-env.ps1
    echo "USERNAME (Output from PowerShell): $env:USERNAME"
    & 'C:\Program Files\Python\3.6\python.exe' -c "import os; print('USERNAME (Output from Python provided from Powershell): $env:USERNAME'); print('USERNAME (Output from Python resolved from Python): {}'.format(os.environ['USERNAME']))"

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1. Case-Sensitivity: Bash is case-sensitive, as opposed to Powershell, which is case-insensitive ↩↩

2. Most Powershell-commands do have aliases, to be equal as the Bash-commands. This can be checked with (e.g for 'ls') get-command ls. Check also for with `get-command new-item ↩

3. Bash: There is no single command to list all avaliable Unix commands. Instead the 'compgen'-command list all available Bash builtins, command-aliases and executables found in the PATH variable ↩

4. Variable-Assignment: In Bash no 'blanks' allowed between variable-name, assignment-operator ('=') and value; Powershell instead allows 'blanks', but needs apostroph, if the value is a string ↩

5. Bash-script using environment variable and calling Python ↩

6. Powershell-script using environment variable and calling Python ↩