Bash

Functions

namename prints the basename without extension
ext prints extension of a file, including “.”

	function namename()
	{
	  local name=${1##*/}
	  local name0="${name%.*}"
	  echo "${name0:-$name}"
	}
	function ext()
	{
	  local name=${1##*/}
	  local name0="${name%.*}"
	  local ext=${name0:+${name#$name0}}
	  echo "${ext:-.}"
	}

Commands

CTRL Key Bound

  • Ctrl + _ = undo
  • Ctrl + @ = set mark
  • Ctrl + a = Jump to the start of the line
  • Ctrl + b = Move back a char
  • Ctrl + c = Terminate the command
  • Ctrl + d = Delete character under the cursor
  • Ctrl + e = Jump to the end of the line
  • Ctrl + f = Move forward a char
  • Ctrl + k = Delete from cursor to EOL
  • Ctrl + l = Clear the screen
  • Ctrl + n = select the next command in history
  • Ctrl + p = select the previous command in history
  • Ctrl + r = Search the history backwards
  • Ctrl + R = Search the history backwards with multi occurrence
  • Ctrl + t = drag character before cursor over the one under the cursor
  • Ctrl + u = Delete backward from cursor
  • Ctrl + v = Insert next character verbatim
  • Ctrl + w = kill word before cursor
  • Ctrl + x = kill backward to the beginning of line
  • Ctrl + xx = Move between EOL and current cursor position
  • Ctrl + x @ = Show possible hostname completions
  • Ctrl + y = paste the text at top of the kill#ring
  • Ctrl + z = Suspend/ Stop the command

ALT Key Bound

  • Alt + ''<'' = Move to the first line in the history
  • Alt + ''>'' = Move to the last line in the history
  • Alt + ? = Show current completion list
  • Alt + * = Insert all possible completions
  • Alt + / = Attempt to complete filename
  • Alt + . = Yank last argument to previous command
  • Alt + b = Move backward
  • Alt + c = Capitalize the word
  • Alt + d = Delete word
  • Alt + f = Move forward
  • Alt + l = Make word lowercase
  • Alt + n = Search the history forwards non=incremental
  • Alt + p = Search the history backwards non=incremental
  • Alt + r = Recall command
  • Alt + t = Move words around
  • Alt + u = Make word uppercase
  • Alt + backspace = Delete backward from cursor

Meta Key Bound

Meta usually corresponds to the Esc key

  • M + f = move forward to the end of next word
  • M + b = move backward to the start of current or previous word
  • M + c = capitalize current word
  • M + d = kill current word
  • M + l = downcase current word
  • M + t = drag the word before cursor over the one under the cursor
  • M + u = uppercase current word
  • M + y = rotate the kill=ring

More Special Keybindings

Here “2T” means Press TAB twice

  • $ 2T = All available commands(common)
  • $ (string)2T = All available commands starting with (string)
  • $ /2T = Entire directory structure including Hidden one
  • $ 2T = Only Sub Dirs inside including Hidden one
  • $ *2T = Only Sub Dirs inside without Hidden one
  • $ ~2T = All Present Users on system from “/etc/passwd”
  • $ $2T = All Sys variables
  • $ @2T = Entries from “/etc/hosts”
  • $ =2T = Output like ls or dir
  • Ctrl + v Ctrl + m = Insert a newline control character

Scripts

Remove the extensions from multiple files

find -type f -name "name.ext" | while read i; do mv $i $i%.ext; done

Rot13 Encryption

In a file:

cat "$@" | tr 'a-zA-Z' 'n-za-mN-Z-A-M'
exit 0

Rename multiple files

for files in $(ls .); do
	  newname=`echo $files | sed 's/oldtext/newtext/g'`;
	  mv $files $newname;
done

Syntax

Various Bash syntax rules

  • ${#variable} = Variable string length
  • variable=$(<file) = Save in variable the content of a file
  • : > file = Delete the content of file (like cat /dev/null). If it didn’t exist, creates a new, empty one
  • ls -l {b*, aa*, cc*} = Multiple selection. Select all files matching the b*, aa* and cc* patterns in a single ls run
  • mkdir -p {aaa,bbb/ccc,def,parent{subdir1,subdir2,subdir3},ppp} = Make whole tree of directories with the same multiple selection syntax as above
  • cmd1 (<cmd2) (<cmd3) (<cmd4) = Send the stdout of the various commands to the preceding one, from right to left. For example: sort (<ls /bin) (<ls /usr/bin) (<ls /opt), which will send the list of files in those 3 directories to sort
  • variable=${1:-123} = Gives variable the value of the first parameter ($1). If this is empty, assign to it 123
  • ${variable##*.} = Corresponds to everything there is in the variable after the period. Generally used with filenames to obtain just the extension
  • ${variable%%.*} = Corresponds to everything there is in the variable before the period. Great to obtain filenames without the extension
  • $RANDOM = Gives back a semi-random number between 0 and 32767
  • [[ string =~ pattern ]] = Returns true if string matches pattern (according to ERE, Extended Regular Expressions). Only for bash >=3.0
  • <<-END = Usually <<END sends the output as it is. With an added - it strips any tab (but still includes whitespaces)
  • declare = Declares various variables: with -a, an array, -A an associative array, -i an integer, -l a string with only lowercase characters, -r a read-only variable, -u a string with only uppercase characters
  • shopt -s extglob = Enables extended globs
  • ^aaa^bbb = Substitutes aaa with bbb in the last executed command on the terminal. Useful to rerun the same command but with different arguments
  • echo ${PIPESTATUS[@]} = Find out all the exit codes of the previously piped commands
  • rm * !("filename") = Remove all files in current directory but for filename. Wildcards can be used to specify the matching like *.ext or filenames? or [!abcde]

Bash History

How to use and navigate through Bash’s history

  • !! = Rerun the last executed command
  • !* = Represent all the arguments of the last executed command
  • !$ = Corresponds to the very last argument of the last executed command
  • !!:2-3 = Corresponds to the list of arguments going from the second to the third of the last executed command. It can also be used like !!:2-$ to represent every argument from the second to the last.
  • !n = Run the command at line n in bash_history
  • !cmd:p = Show the last time cmd was executed, with all its arguments and parameters
  • !cmd = Rerun, with same arguments and parameters, last execution of cmd
  • !!:gs/oldarguments/newarguments = Rerun last executed command substituting oldarguments with newarguments

Bash Redirection

Partly copied/modified from bash-redirections-cheat-sheet

  • cmd > file = redirect stdout to file. Also cmd 1> file
  • cmd 2> file = redirect stderr to file
  • cmd >> file = append stdout to file
  • cmd &> file = redirect stdout and stderr to file. Also cmd > file 2>&1
  • cmd <<< "string" = redirect a single line of text to the stdin of cmd
  • exec 2> file = redirect stderr of all commands to a file forever
  • exec 3< file = open a file for reading using a custom file descriptor
  • exec 3> file = open a file for writing usint a custom file descriptor
  • exec 3<> file = open a file for reading and writing using a custom file descriptor
  • exec 3>&- = close a file descriptor
  • exec 4>&3 = make file descriptor 4 to be a copy of 3. With exec 4>&3- also close 3
  • echo "abc" >&3 = write to custom file descriptor 3
  • cat <&3 = read from custom file descriptor 3
  • (cmd1; cmd2) > file = redirecto stdout from multiple commands to a file (using a sub-shell). Or with { cmd1; cmd2 } > file, without using a sub-shell
  • exec 3<> /dev/tcp/host/port = open a tcp connection to host:port. With /dev/udp/host/port opens a udp connection
  • cmd1 |& cmd2 = redirect stdout and stderr of cmd1 to stdin of cmd2. This is for bash 4.0+ only, for older versions use cmd1 2>&1 | cmd2
  • exec {filew}> file = open a file for writing using a named file descriptor called {filew}. Bash 4.1+ only
  • cmd 3>&1 1>&2 2>&3 = swap stdout and stderr of cmd
  • cmd > >(cmd1) 2> >(cmd2) = send stdout of cmd to cmd1 and stderr of cmd to cmd2

Terminal Line Wrapping

To prevent commands to overlap on the prompt, add a \ before every [ and ] in your bash prompt ($PS1)