Shortcuts
ctrl-a # Move to the start of line
ctrl-e # Move to end of a line
ctrl-k # Remove (Cut) text after the cursor
ctrl-y # Yank text (Copy)
ctrl-r # Search previous command from history
Shell Basics
- Export variable to the environment. All child processes will get this variable:
export varname=value - Display current Shell Variables
set | sort - Set and Unset Shell Options:
shopt -s <option> # Set shell option shopt -u <option> # Unset shell option - Create symbolic link
ln -s /path/to/file /path/to/symlink - Pass STDOUT and STDERR to /dev/null:
command > /dev/null 2>&1 - Time Stamps
stat file:- Access - the last time the file was read
- Modify - the last time the file was modified (content has been modified). Virtually, every modify is create.
- Change - the last time meta data of the file was changed (e.g. permissions) To display this information, you can use stat which is part of the coreutils.
- Command Substitution $(command)
Built-In VS External
$ echo 'Echoed with a built-in!'
Echoed with a built-in!
$ /bin/echo 'Echoed with external program!'
Echoed with external program!
# type command will return what type of command it is (built-in vs external)
$ type echo
echo is a shell builtin
$ type ls
ls is hashed (/bin/ls)
Links
Use -f to force overwrite
ln -s source_file target_file # -s is for symbolic
Brace Expansion
$ echo {one,two,red,blue}fish
onefish twofish redfish bluefish
$ echo fish{one,two,red,blue}
fishone fishtwo fishred fishblue
$ echo fi{one,two,red,blue}sh
fionesh fitwosh firedsh fibluesh
echo foo{1,2,3}.txt # Output: foo1.txt foo2.txt foo3.txt
cp -v file1.txt{,.bak} # Output: file1.txt -> file1.txt.bak
echo file{a..d}.txt # Output: filea.txt fileb.txt filec.txt filed.txt
mkdir -p /apache-jail/{usr,bin,lib64,dev} # Make multiple dirs
mv file.{txt,doc} # Rename file.txt to file.doc
Permissions
find /home/user -type d -print0 | xargs -0 chmod 0775
find /home/user -type f -print0 | xargs -0 chmod 0664
# Permissions:
1 – "can execute"
2 – "can write"
4 – "can read"
# Examples:
chmod 600 file – owner can read and write
chmod 700 file – owner can read, write and execute
chmod 666 file – all can read and write
chmod 777 file – all can read, write and execute
Command Substitution
$ date +%d-%b-%Y
12-Mar-2004
$ today=$(date +%d-%b-%Y)
$ echo $today
12-Mar-2004
# listing of all the files from all the RPM packages that have httpd in the name
$ rpm -ql $(rpm -qa | grep httpd)
# Star will substitue for all files
$ for file in * ; do cp $file $file.bak; done