Handy command-line aliases and tricks

[mssever]

I often find that filesystem tasks are quicker from the command line. So, I've compiled some of my favorite aliases and tricks. Note that these have only been tested in bash (bash is the default shell--or command interpreter--in most flavors of Linux, including Ubuntu).

Command Editing

Tab completion: type part of a command name or filename and hit tab. Bash will automatically fill in as much as it can unambiguously. If you hit tab twice, bash will show you a list of commands/filenames that match what you've typed so far.

Searching through your history: If you hit ^R (Ctrl+R) then start typing, bash will display the last match from your command history. Hit enter to execute the displayed command, left or right arrow to edit the command, or ^C to cancel.

Job Control

Typing ^Z stops a program without exiting and gives you back a command line. You can use this to do several things at once. Type fg to bring the program back to the front or bg to tell it to resume in the background. Append an ampersand (&) to the end of a command to start a program in the background. Type jobs for a list of current jobs.

Let's not forget to mention one of the greatest tips -- how to cancel any running program in CLI ! Ctrl+C.

Aliases

Aliases are shortcuts to commands you use often. They can save you from having to remember certain options that you usually use. To create an alias, type alias alias_name='aliased_command --options', making substitutions where appropriate. type unalias alias_name to remove an alias and alias without any options to see the aliases that are currently defined.

Examples: Here are some of the aliases I use.

#Aliases for improved directory listings
#The --color=tty option shows items in different colors according to their type.
#For example, directories are blue, executable files are green, symlinks are cyan, etc.
#The -F option appends a symbol after entries to indicate their types.
#You might not like both options at the same time.
alias ls='ls -F --color=tty' #regular ls
alias l.='ls -dF .[a-zA-Z0-9]* --color=tty' #only show dotfiles
alias ll='ls -lhF --color=tty' #long listing

#Make these commands ask before clobbering a file. Use -f to override.
alias rm="rm -i"
alias cp="cp -i"
alias mv="mv -i"

#Use human-readable filesizes
alias du="du -h"
alias df="df -h"

#Miscellaneous
alias bzip2='bzip2 -v'
alias j=jobs
alias cd..="cd .." #work around a common typo

#Automatically do an ls after each cd
cd() {
  if [ -n "$1" ]; then
    builtin cd "$@" && ls
  else
    builtin cd ~ && ls
  fi
}

Saving for future use: There are a number of ways to do this, but the way I prefer is to create a file in your home directory called .alias and put all your aliases there. Then insert the following at the end of $HOME/.bashrc

# Source the aliases, if a separate file exists
if [ -e $HOME/.alias ]; then
  [ -n "$PS1" ] && . $HOME/.alias
fi

To apply your changes to the current session, type source $HOME/.bashrc

Setting the Prompt

You can change your prompt by setting $PS1 and $PS2 in ~/.bashrc. There are many ways to do this. Here's what I have in my .bashrc:

# Set the prompt
function setPrompt {
  local COLOR1="\[\033[1;33m\]"     #First color
  local COLOR2="\[\033[0;33m\]"     #Second color
  local NO_COLOR="\[\033[0m\]"      #Transparent - don't change

  case $TERM in
    xterm*)
      local TITLEBAR="\[\033]0;\h - \w\007\]"
      ;;
    *)
      local TITLEBAR=""
      ;;
  esac

  PS1="${TITLEBAR}${COLOR1}\w${COLOR2}:\\$ ${NO_COLOR}"
  PS2="${COLOR2}--${COLOR1}> ${NO_COLOR}"
}

setPrompt
unset setPrompt

I set different colors for different machines. For example, I have

local COLOR1="\[\033[1;32m\]"
local COLOR2="\[\033[1;34m\]"

on my server and

local COLOR1="\[\033[7;1;31m\]"
local COLOR2="\[\033[7;1;31m\]"

for my root prompt. For root, I also set

local TITLEBAR="\[\033]0;ROOT - \w - \u@\h - ROOT\007\]"

Attached is a script that lists some of the various color codes.

Exit status: In addition, the following code displays the exit status of the last command, if nonzero:

#Not my code; I don't remember where I got it.
#Determine and display the exit Status of the last command, if non-zero.
function checkExitStatus() {
  local status="$?"
  local signal=""
  local COLOR1="\033[0;0;33m"     #First color
  local COLOR2="\033[0;0;36m"     #Second color
  local NO_COLOR="\033[0m"        #Transparent - don't change

  if [ ${status} -ne 0 -a ${status} != 128 ]; then
    # If process exited by a signal, determine name of signal.
    if [ ${status} -gt 128 ]; then
      signal="$(builtin kill -l $((${status} - 128)) 2>/dev/null)"
      if [ "$signal" ]; then
        signal="$signal"
      fi
    fi
    echo -e "${COLOR1}[Exit ${COLOR2}${status} ${signal}${COLOR1}]${NO_COLOR}" 1>&2 ${COLOR2}${signal}${COLOR1}]${NO_COLOR} " 1>&2
    fi
  return 0
}

PROMPT_COMMAND=checkExitStatus

Scripts

Here are a couple of other scripts that are handy:

Listing processes: This script is a shortcut to ps -ef | grep foo. Save in in your path as p and make it executable. For usage instructions, type p --help.

#!/bin/bash
#
# Shortcut to ps -ef | grep foo

GREP="|grep"
CMD="ps -ef"
CMD2=
finalStr=
commandStr="/bin/bash $0"

printHelp() {
    echo -e "Shortcut to \"ps -ef | grep foo\"\n"
    echo "Usage: $(basename "$0") [-i] [-v] pattern1 [pattern2 [pattern3 [...]]]"
    echo "-i: case-insensitive grep"
    echo "-v: inverse grep: return lines that do NOT match the pattern"
    exit
}

for i in "$@"; do commandStr="$commandStr $i"; done

for i in "$@"; do
    getopts ivh option
    if   [ $option == i ]; then GREP="${GREP} -i"
    elif [ $option == v ]; then GREP="${GREP} -v"
    elif [ $option == h -o "$i" == "--help" ]; then printHelp; fi
done

for i in "$@"; do
    if [ "$i" == "-i" -o "$i" == "-v" -o "$i" == "-vi" -o "$i" == "-iv" ]; then shift
    else break; fi
done

for i in "$@"; do CMD2="${CMD2}${GREP} \"$i\""; done

finalStr="${CMD}${CMD2} | grep -v 'ps -ef' | grep -v ' grep ' | grep -v '/grep ' | grep -v '$commandStr'"

eval $finalStr

Recursive Shredding: The shred command securely erases files. Great. But it doesn't work recursively (you can't give it a directory, for example). This script does. Save in in your path and make it executable. Do name_you_called_it --help for instructions.

#!/bin/bash

EXIT_VAL=0
progName="$(basename "$0")"
verStr="Recursive Shredder 0.1"

FILE_COLOR="\033[4;34m"
ERROR_COLOR="\033[0;31m"
DONE_COLOR="\033[0;32m"
NO_COLOR="\033[0m" #Transparent - don't change

licTxt() {
    echo "Copyright (c) 2006 by Scott Severance"
    echo "Licensed under the terms of the GNU General Public License"
    echo
    echo "This software is provided \"AS-IS\" and carries NO WARRANTY. Use it at your own risk."
}

shredThis() {
    #echo "press any key"
    #read -sn 1
    if [ -d "$1" -a "$1" != "." -a "$1" != ".." ]; then
        local oldDir="$(pwd)"
        builtin cd "$1"
        echo -e "Entering directory: ${FILE_COLOR}$(pwd)${NO_COLOR}"
        #pwd
        for i in * .*; do
            if [ "$i" != "." -a "$i" != ".." -a "$i" != "*" ]; then
                shredThis "$i"
            fi
            done
        builtin cd "$oldDir"
        echo -e "Removing directory: ${FILE_COLOR}${1}${NO_COLOR}"
        echo -ne $ERROR_COLOR
        rmdir "$1"
        echo -ne $NO_COLOR
        #echo -n "Returning to "
        #pwd
    

    elif [ -L "$1" -o -p "$1" -o -S "$1" ]; then # test for symlinks, fifos, and sockets
        echo -ne "Deleting special file ${FILE_COLOR}${1}${NO_COLOR}... "
        echo -ne $ERROR_COLOR
        rm "$1"
        echo -ne $NO_COLOR
        local rslt="$?"
        if [ "$rslt" -ne "0" ]; then
            echo -e "${ERROR_COLOR}### ERROR deleting ${FILE_COLOR}${1}${ERROR_COLOR}: rm exited with status ${rslt}. Aborting. ###${NO_COLOR}" > /dev/stderr
            exit 127
        fi
        echo -e "${DONE_COLOR}Done${NO_COLOR}"

     elif [ -f "$1" ]; then
        echo -ne "Shredding ${FILE_COLOR}${1}${NO_COLOR}... "
        echo -ne $ERROR_COLOR
        shred --zero --remove "$1"
        echo -ne $NO_COLOR
        local rslt="$?"
        if [ "$rslt" -ne "0" ]; then
            echo -e "${ERROR_COLOR}### ERROR shredding ${FILE_COLOR}${1}{$ERROR_COLOR}: shred exited with status ${rslt}. Aborting. ###${NO_COLOR}" > /dev/stderr
            exit 127
        fi
        echo -e "${DONE_COLOR}Done${NO_COLOR}"

    else
        echo -e "${ERROR_COLOR}### NOTICE: The file ${FILE_COLOR}${1}${ERROR_COLOR} is not a regular file. Skipping. ###${NO_COLOR}" > /dev/stderr
        EXIT_VAL=3
    fi
}

if [ "$1" = "--no-color" ]; then
    FILE_COLOR=""
    ERROR_COLOR=""
    DONE_COLOR=""
    NO_COLOR=""
    shift
fi

if [ "$#" = "0" -o "$1" = "--help" ]; then
    echo -e "${DONE_COLOR}${verStr}${NO_COLOR}" > /dev/stderr
    echo > /dev/stderr
    echo "Usage: $progName [--no-color] file-or-directory-1 file-or-directory-2 ..." > /dev/stderr
    echo "       $progName --help" > /dev/stderr
    echo "       $progName --version" > /dev/stderr
    EXIT_VAL=1

elif [ "$1" = "--version" ]; then
    echo -e "${DONE_COLOR}${verStr}${NO_COLOR}"
    echo
    licTxt
    EXIT_VAL=2

else
    for i in "$@"; do
        if [ "$i" = "." ]; then i="$(pwd)"; fi
        shredThis "$i"
    done
fi

exit $EXIT_VAL

Other Tips

If you have any other aliases, etc. that might be useful to others, please add them here.