A Bash alias allows the user to launch any command or group of commands (including options and filenames) by entering a single word.

Aliases are very convenient to use for frequently used commands.

For example, here the alias c is created against clear command.

alias c='clear'

Instead of typing clear to clear the screen only the letter c is needed (and the [ENTER] key).

c

My Aliases

Create the file /etc/profile.d/bash_aliases.sh which will contain all the aliases.

/etc/profile.d/bash_aliases.sh

# Instruct bash to expand the arguments to aliases.
shopt -s expand_aliases
 
#-------------------------------------------------------------
# Protection for these commands; which will prompt before overwriting.
#-------------------------------------------------------------
# Do not delete / and prompt before deleting.
alias rm='rm -i --preserve-root'
 
alias cp='cp -i'
alias mv='mv -i'
alias ln='ln -i'
 
# Preventing changing perms on /
alias chown='chown --preserve-root'
alias chmod='chmod --preserve-root'
alias chgrp='chgrp --preserve-root'
 
alias rmdir='rm -Rf $1'
 
#-------------------------------------------------------------
# cd
#-------------------------------------------------------------
# To pick up when user forgets the space.
alias cd..='cd ..'
 
# Uses cd() function = pushd,·
# b = go backwards (popd), f = go forwards (kind of like "unpopd").
alias d='dirs'
alias b='pushd +1'         # go backwards (popd).
alias f='pushd -0'         # go forwards (kind of like "unpopd").
 
 
#-------------------------------------------------------------
# Disk
#-------------------------------------------------------------
alias du='du -kh'          # Human-readable format.
alias dutotal='du -ch 2> /dev/null |tail -1'  # Displays only the total.
alias dutop10='du -hsx * | sort -rh | head -10'  # What is using the most space.
 
alias df='\df -kTh;\df -Thl --total | grep total'  # Adds total to the df command.
 
# Shows the individual partition usages without the temporary memory values.
alias dfx='\df -kThl --exclude-type=tmpfs --exclude-type=devtmpfs'
 
#-------------------------------------------------------------
# Directories.
#-------------------------------------------------------------
alias mkdir='mkdir -p'     # Make parent directories if needed.
alias back='cd $OLDPWD'    # Return to the last directory you were in.  Same as 'cd -'.
 
#-------------------------------------------------------------
# Downloading.
#-------------------------------------------------------------
alias wget='wget -c'       # -c flag to continue download in case of problems.·
alias wgetpage='wget --html-extension --recursive --convert-links --page-requisites --no-parent $1'
 
#-------------------------------------------------------------
# Files.
#-------------------------------------------------------------
alias fcount='ls -l | wc -l' # File count.
alias fcounta='ls -la | wc -l' # File count (incl hidden files).
alias fcountr='find . -type f | wc -l' # File count recursive.
alias lastmodified='find -type f -print0 | xargs -r0 stat -c %y\ %n | sort'
alias nocomment='grep -Ev "^(#|$)"'  # Show text file without comment (#) lines; or empty lines.
 
alias bigfiles='find . -type f 2>/dev/null | xargs du -a 2>/dev/null | awk "{ if ( \$1 > 5000) print \$0 }" | sort -hr'
alias verybigfiles='find . -type f 2>/dev/null | xargs du -a 2>/dev/null | awk "{ if ( \$1 > 500000) print \$0 }" | sort -hr'
 
alias brokenlinks='\find . -xtype l -printf "%p -> %l\n"'  # Find broken symlinks.
 
# count files by type - http://www.shell-fu.org/lister.php?id=173
alias ftype="find ${*-.} -type f | xargs file | awk -F, '{print $1}' | awk '{$1=NULL;print $0}' | sort | uniq -c | sort -nr"
 
# Show diffs between files
alias fdiff='grep -F -x -v -f $1 $2'
 
#-------------------------------------------------------------
# File Permissions.
#-------------------------------------------------------------
alias fperm="find . -type f -exec chmod 0644 '{}' \;"
alias dperm="find . -type d -exec chmod 0755 '{}' \;"
 
#-------------------------------------------------------------
# Greps.
#-------------------------------------------------------------
alias grep='grep --color=auto'  #·
alias egrep='egrep --color=auto'  #
alias fgrep='fgrep --color=auto'  #
alias grepall='find . -name "*" | xargs grep --color=auto '
 
#-------------------------------------------------------------
# Logs.
#-------------------------------------------------------------
# alias syslog='sudo tail -10f /var/log/syslog'  # Follow syslog.
# alias messages='sudo tail -10f /var/log/messages'  # Follow messages.
 
# Last 10 items within every log file.
alias logs='tail -f /var/log/{dmesg,messages,*{,/*}{log,err}}'
 
#-------------------------------------------------------------
# ls.  (Assumes you use a recent GNU ls).
#-------------------------------------------------------------
alias ls='ls -h --color=auto'  # Add colors and human-readable sizes by default on 'ls'.
alias lsa='ls -A'          # Show hidden files.
alias lsd='ls -d */ >/dev/null 2>/dev/null; [ $? -eq 0 ] && ls -d */ || : ;'  # List only directories, if any exist.
alias lsdf='ls -v --group-directories-first'  # Directories first, with alphanumeric sorting.
alias lsdt='ls -h --group-directories-first --time-style=+"%d.%m.%Y %H:%M" --color=auto -F'
alias lse='ls -AF | grep \*'  # Show executables only.
alias lsh='ls -Am'         # List files horizontally, comma-separated.
alias lsm='ls -Al |more'   # Pipe through 'more'.
alias lsne='ls -AF | grep -v \*'  # Show non executables only.
alias lsnx='ls -AF | egrep -v "\.|/"'  # Show only file without an extension.
alias lsr='ls -lR'         # List files recursively.
alias lssh='ls -Ax'        # Sort by name horizontally.
alias lsss='ls -Sr'        # Sort by size, biggest last.
alias lsssh='ls -shAxSr'   # Sort by size, biggest last, horizontally.
alias lsst='ls -Atr'       # Sort by date, most recent last
alias lssta='ls -Atur'     # Sort by/show access time,most recent last.
alias lsstc='ls -Atcr'     # Sort by/show change time,most recent last.
alias lssx='ls -AXB'       # Sort by extension.
alias lsx='ls -AF | egrep "\.|/"'  # Show only file with an extension.
 
alias ll='ls -lF'          # Long listing, classify.
alias lla='ls -lAF'        # All files, long listing.
alias lld='ls -lFA | grep :*/'  # List only directories, if any exist.
alias lldf='ls -lv --group-directories-first'  # Directories first, with alphanumeric sorting.
alias lldt='ls -lh --group-directories-first --time-style=+"%d.%m.%Y %H:%M" --color=auto -F'
alias lle='ls -lFA | grep \*'  # Show executables only.
alias llm='ll |more'       # Pipe through 'more'
alias llne='ls -lFA | grep -v \*'  # Show non executables only.
alias llnx='ls -lFA | egrep -v "\.|/"'  # Show only file without an extension.
alias llr='ll -lAR'        # Recursive ls.
alias llss='ls -lSr'       # Sort by size, biggest last.
alias llst='ls -lAtrh'     # Sort by date, most recent last, and human readable
alias llsta='ls -ltur'     # Sort by/show access time,most recent last.
alias llstc='ls -ltcr'     # Sort by/show change time,most recent last.
alias llsx='ls -lXB'       # Sort by extension.
alias llx='ls -lFA | egrep "\.|/"'  # Show only file with an extension.
 
alias tree='find . | sed "s/[^/]*\//|   /g;s/| *\([^| ]\)/+--- \1/"'  # Simple tree of current dir.
 
#-------------------------------------------------------------
# Memory.
#-------------------------------------------------------------
alias mem='echo -e Memory usage: $(free -h | grep "+" | cut -c26-30)/ $(free -h | grep "Mem:" | cut -c15-18)'
 
#-------------------------------------------------------------
# Misc.
#-------------------------------------------------------------
alias mount='mount | column -t'   # Make mount command output pretty and human readable format.
alias pause='read -n 1 -p "Press any key to continue…"'
alias restart='killall -SIGUSR1'
alias utf='iconv -f ISO-8859-1 -t UTF-8'
alias which='type -a'      # Includes aliases.
 
#-------------------------------------------------------------
# Networking.
#-------------------------------------------------------------
alias connections='sudo /usr/bin/lsof -i -P'
alias openports='netstat -lntp 2>/dev/null | grep -v " - *$"'  # Shows open ports.
alias macs='ifconfig | grep HWaddr'  # Shows MAC addresses for all nics.
alias nics='ifconfig em1 | egrep "[0-9]{1,3}(\.[0-9]{1,3}){3}"'  # Shows all nics.
alias ping='ping -c 5'  # Stop after sending count ECHO_REQUEST packets.
alias fastping='sudo ping -c 5 -s.2'  # Do not wait interval 1 second, go fast.
 
# Network diagnostic.
# Usage: mtr google.com
alias trace='mtr --report-wide --curses $1'
 
#-------------------------------------------------------------
# Path.
#-------------------------------------------------------------
# Pretty-print of some PATH variables:
alias path='echo -e ${PATH//:/\\n}'
alias libpath='echo -e ${LD_LIBRARY_PATH//:/\\n}'
 
#-------------------------------------------------------------
# Processes.
#-------------------------------------------------------------
alias psc='ps h -eo pcpu,pmem,pid,comm,user,cputime | sort -nr | head'
alias psm='ps h -eo pmem,pcpu,pid,comm,user,cputime | sort -nr | head'
alias pstree='ps -e -o pid,args --forest'
alias psfull='ps -auxwww'  # ps with wide output so you can see full commands.
 
# usage: psg peter
# usage: psg ssh
alias psg='ps -Helf | grep -v $$ | grep -i -e WCHAN -e '  # ps grep.
 
# Show only my procs.
alias myps='ps -fHu $USER'     # if not $USER, try $LOGIN
 
#-------------------------------------------------------------
# Programming – C/C++/Java/PHP.
#-------------------------------------------------------------
# Count lines of php code under the current directory.
alias countphp='find . -name "*.php" -print0 | xargs -0 wc'
 
# Count lines of java code under the current directory.
alias countjava='find . -name "*.java" -print0 | xargs -0 wc'
 
# Count lines of C or C++ or Obj-C code under the current directory.
alias countc='find . \( -name "*.c" -or -name "*.cpp" -or -name "*.h" -or -name "*.m" \) -print0 | xargs -0 wc'
 
# Count lines of C or C++ or Obj-C or Java or PHP code under the current directory.
alias countcode='find . \( -name "*.c" -or -name "*.cpp" -or -name "*.h" -or -name "*.m" -or -name "*.java" -or -name "*.php" \) -print0 | xargs -0 wc'
#-------------------------------------------------------------
# Spelling typos.  Highly personal and keyboard-dependent.
#-------------------------------------------------------------
alias xs='cd'
alias vf='cd'
alias moer='more'
alias moew='more'
alias kk='ll'
 
#-------------------------------------------------------------
# Time.
#-------------------------------------------------------------
alias now='date +"%T"'
alias nowtime=now
alias nowdate='date +"%Y-%m-%d"'
 
#-------------------------------------------------------------
# Web.
#-------------------------------------------------------------
# Pass it via sudo so whoever is admin can reload it without calling you.
alias nginxreload='sudo /usr/sbin/nginx -s reload'
alias nginxtest='sudo /usr/sbin/nginx -t'

Set the file owner and permissions:

chown root:root /etc/profile.d/bash_aliases.sh
chmod 644 /etc/profile.d/bash_aliases.sh