smproj-nsh

A semester project about writing a shell.

What does it implement?

• Executing commands
• Backslash quoting and single quote quoting
• Pipeline
• Internal variable
• (Partial) IO redirection
• Executing commands and pipelines in background
• Alias substitution
• Basic parameter expansion
• History (through GNU readline, saves them at ~/.nsh_history)
• Line editing (through GNU readline)
• (Partial) File name completion
• (Partial) History substitution

How to build it?

mkdir build
cd build
qmake ../nsh.pro
make

Some examples that will run on it?

# Long pipeline
cat /etc/os-release | sed -e 's/=/ /' -e '/^\s*$/d' | awk '{print $1;}' | sort | uniq

# Execute a pipeline in background
uname -a | tr ' ' '\n' &

# Pipeline and IO redirection
</etc/os-release cat | tr '=' '\n' > /tmp/foobar
cat /tmp/foobar

# History substitution
ls /
!! -la
!! --color
sudo !!

# alias
alias ll='ls -la'
ll
alias ls='ls --color'
ll /
alias foobar='cat /etc/os-release | wc -l'
foobar

# unalias
alias
alias ll
unalias ll
ll  # will raise an error

# history
history
history 10
HISTSIZE=5
history
HISTSIZE=

# Internal variable
FOO=BAR
echo $FOO
bash -c 'echo $FOO'

# Environment variable
export FOO=lorem
export
bash -c 'echo $FOO'
unexport FOO
bash -c 'echo $FOO'