#!/usr/bin/env bash
    
    #Copy file contents into Clipboard ("ctrl+c")
    xclip -sel c < file
    
    
    ### Buffers and redirect ###
    
    #buffers 0=STDIN, 1=STDOUT, 2=STDERR, then 3 up to 9 are available for use
    
    #exec without command argument will redirect IO for current program e.g.
    #send stdout to /dev/null via file descriptor 9
    exec 9>/dev/null 1>&9
    #restore stdout so we can see it
    exec &>/dev/tty
    
    # example of redirect, get use to this //Gustav
    cat < my_file.txt > my_new_file.txt
    
    ### Man pages ###
    
    man #regular man pages
    help #for help bash
    apropos #search man pages (man)
    
    ### Symlinks and inodes ###
    
    readlink #shows symlink info, also see f flag
    
    #hardlink points to underlying inode so multiple can exist, and as long as any do exist the inode cannot be overwritten
    #hardlink cannot point to folder as this would create loops
    #however, symbolic (soft) links can point to folders since `readlink` shows the real path.
    
    
    #use `stat` to see amount of (hard) links to a file, and other such info
    stat
    readlink
    ln a b
    ln -s a b
    
    ### Bash shortcuts ###
    
    #0th argument of last command
    echo !:0
    
    #return from last command ("error code") for C errors see errno
    echo $?
    
    
    ### grep, sed, awk
    
    #the tools grep, sed, and awk are usually available on a Linux system and can be used for different purposes,
        # although it's often a matter of taste.
    # These tools all use regular expressions (regex),
        # awk  - extended regex
        # sed  - regex (-E for extended)
        # grep - regex (-E for extened)
    
    # grep together with the default programs in Linux (core utilities) can perform many basic operations
        # grep, cut, wc, head, tail, strings, ...
        # These can also be used together with sed, awk, or other tools
    # sed is good for a lot of things, especially text modification e.g. search and replace stuff
        # example: find all headers (# ## ### etc) and add AS MANY # to the end of line
    # awk, can use more advanced statements as well as variables and arrays to count and sum results,
        # thereby easily maintain data over multiple lines.
        # awk also supports delimiters to further split the rows into smaller fields.
    
    
    ####### The rest of this document shows examples of text manipulation #######
    
    
    ### SED append corresponding nr of '#' ###
    
    #save starting '#' (at least 1) to group and append last to line
    #s/ for search and replace
    #\) group hits for later use as \1 and \2 ('#' and rest of text)
    #Note that spaces have a meaning for the matching
    #find rows starting with AT LEAST one '#' and save as first group,
        # the rest '.*' (all chars) to the end of row ($) save as second group.
        # Finally the text is printed as \1 \2 \1, i.e. the starting '#' are repeated at the end.
    
    sed -i "s/^\(##*\)\(.*\)$/\1\2 \1/" example_doc.txt
    
    #extended regex
    sed -i -E "s/^(#+)(.*)$/\1\2 \1/" example_doc.txt
    
    
    ### Find users with bash as shell ###
    
    #use cut to get first word before delimiter :
    grep "/bin/bash" /etc/passwd | cut -d \: -f 1
    
    #find lines ending with 'bash', each hit perform search and replace
    sed -E "/.*bash$/ { s/^(\w*).*$/\1/;p };d" < /etc/passwd
    
    #set separator ':', match regex, and print first string (before separator)
    awk -F: '/bash/{ print $1 }' < /etc/passwd
    
    
    ### Lines without word ###
    
    grep -v "daemon" /etc/group
    
    sed -E "/daemon/d" < /etc/group
    
    awk '!/daemon/' < /etc/group
    
    
    ### Count hits and show relevant lines ###
    
    #print matching lines numbers
    awk '/localhost/{print "Line " NR " matches"}' < /etc/hosts
    
    # Count nr of hits (i) and matching line numbers (NR)
    # TODO this seems broken!
    #awk '/localhost/{i=0}{i++} /localhost/{print "Line " NR " matches"} END {print i " hits"}' < /etc/hosts
    
    
    ### List files with numbers (exclude folders) ###
    
    #ls -p to list folders with / at the end
    ls -p /etc/ | grep -v ".*/$"| grep "[0-9]"
    
    ls -p /etc/ | awk "! /.*\/$/ && /[0-9]/"
    
    #delete lines ending in /, then print remaning lines which contains at least a number, delete all lines
    ls -p /etc/ | sed -E "/\/$/ d; /[0-9]/ p; d"
    
    
    ### SUM variables with awk ###
    
    #If third argument delimted by : only contains digits add it to sum
    awk -F ':' '$3 ~ /^[0-9]+$/ {sum+=$3} END {print sum}' < /etc/passwd
    
    
    ### AWK DIV ###
    
    #BEGIN {
    #    # Things to be done before you start processing rows.
    #}
    #{
    #    # Things to be done for each row.
    #}
    #END {
    #    # Things to be done after processing the last row.
    #}
    
    
    ### Div ###
    
    #simple find exact filename
    ls /usr/share/doc -R | grep "^README$"