bash Shell

Variables

export  # shows global (exported) variables
set  # shows all variables
set | less  # pipe output of set to input of less
q  # quit less
export PAGER=/usr/bin/pg  # assign a value, mark as global
man man  # now paged with pg rather than less (different prompt)
q Enter  # quit the pg pager
Test1=foo  # assign a string value to a variable
echo $Test1  # substitute the value of the variable, show the result
Test2=$(whoami)  # substitute the output of a command
echo $Test2
set  # look for Test1 and Test2
unset Test1 Test2  # remove definitions
set  # look for Test1 and Test2

Substutution & Quoting

echo $PS1  # show your primary command prompt string
OLDPS1=$PS1  # save your existing command prompt
PS1=date$
PS1=$(date)$
PS1=$(date)$\   # IMPORTANT - put a space after the \
PS1="$(date)$ "
echo $PS1  # shows the string you assigned above (substitution done)
PS1='$(date)$ '
echo $PS1  # shows the string you assigned above (substitution not done)
PS1=$OLDPS1  # restore your original command prompt

Alias

alias ll='ls -al'  # (lowercase LL) this creates an alias (abbreviation)
ll  # this should give you a long listing of all files
alias  # this shows all currently defined aliases
unalias ll  # remove the alias
ll  # error message

Built-in Commands

type cd  # shows type of command (builtin)
type cat  # pathname of executable file
type ls  # alias (abbreviation)
which ls  # shows path to ls executable
ls -l $(which ls)  # details
time ls  # shows execution time (not time of day)

Options

set -o  # this will show your options
set -o ignoreeof  # prevents Ctrl+d from logging you out
Ctrl+d  # this won't work now, but exit and logout will
set -o noclobber  # prevents redirected output from clobbering a file
cat > testfile  # create a file
original  # type this line
Ctrl+d
cat testfile  # show the contents
cat > testfile  # this won't work now
cat testfile  # show the contents
cat >> testfile  # this is OK, appends rather than overwrites
appended  # type this line
Ctrl+d
cat testfile
set +o noclobber  # unset the option
cat > testfile  # now you can clobber the file
clobbered  # type this line
Ctrl+d
cat testfile

Redirect Input

mail -s 'test' $USER < testfile  # email a file to yourself  by redirecting input
mail  # read email interactively, ? prompt
1 Enter  # read message 1
q Enter  # quit mail
cat > testfile < /dev/null  # overwrite with nothing
cat testfile

Redirect Error

ll 2> err  # redirect error messages
cat err
ll 2> /dev/null  # discard
rm err  # clean up

Configuration

less /etc/profile  # system-wide config for Bourne shell family, for login shells
q  # quit less when done
less ~/.profile  # user config for Bourne shell family, for login shells
q  # quit less when done
less /etc/bash.bashrc  # system-wide config for Bash, for non-login interactive shells
q  # quit less when done
less ~/.bashrc  # user config for Bash, for non-login interactive shells
q  # quit less when done
less ~/.bash_logout  # commands for Bash shell to run at logout
q  # quit less when done
echo $PATH  # shell variable containing directories to search for commands
apache2 -V  # not found (directory not in $PATH)
PATH=$PATH:/sbin:/usr/sbin  # add system directories to $PATH
apache2 -V  # runs (shows version)
# for FreeBSD use /usr/local/sbin/httpd -V