demo.bash

#!/bin/bash

echo "Welcome to part two of the bash series. This presentation assums you have a basic understanding of what the shell is, and how it interacts with the operating system."
echo 
echo "We are going to cover creating, reading, searching, and destroying files. Mastering file operations is the first step twords command line proficiency."
echo "This script works by showing you an explaining sentence, pressing enter will then show you the associated command, and pressing enter again will run that command."
echo
echo "It's bashing time!"

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echo "Let's make a file."
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echo "% touch new_file.txt"
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touch new_file.txt

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echo "Now we need to set access on the file to 'writeable'"
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echo "% chmod +w new_file.txt"
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chmod +w new_file.txt

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echo "Let's see what is in this new file."
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echo "% cat new_file.txt"
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cat new_file.txt

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echo "Nothing yet, so I'll add some random text to it."
echo "For extra credit, come back to this part of the script and try to figure out what it is doing."
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# declairing a variable in bash
cool_thing_to_say="Neutra Odd Future High Life, you probably haven't heard of them art party selvage narwhal street art chillwave paleo yr pour-over Intelligentsia umami wayfarers. Truffaut drinking vinegar Etsy, forage lo-fi leggings locavore ennui plaid vinyl stumptown 8-bit cardigan. Wes Anderson dreamcatcher chia next level, tousled fingerstache hella umami photo booth quinoa Tumblr kitsch vinyl. Portland quinoa banjo readymade. Sustainable selfies hashtag leggings fap. Godard Neutra DIY whatever gastropub. Mlkshk banh mi DIY, Neutra +1 Godard Helvetica Blue Bottle."
a=($cool_thing_to_say)  # create an array 
num_words=${#a[*]}      # Count the number of words in the array

# loop from 1 to 300 and randomly echo a set of 3 random words from our array into the new file
for i in {1..300}
do
  echo "${a[$((RANDOM%num_words))]} ${a[$((RANDOM%num_words))]} ${a[$((RANDOM%num_words))]}" >> new_file.txt
done

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echo "And now we can view that file a few different ways"

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echo "The whole file at once"
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echo "% cat new_file.txt"
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cat new_file.txt

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echo "The whole file, including hidden end of line chars"
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echo "% cat -v new_file.txt"
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cat -v new_file.txt

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echo "How about just the first 5 lines?"
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echo "% head -5 new_file.txt"
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head -5 new_file.txt

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echo "Last 5 lines"
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echo "% tail -5 new_file.txt"
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tail -5 new_file.txt

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echo "Here is how you 'follow' a file, very usefull for watching log files"
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echo "% tail -f new_file.txt"


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echo "Lets open up the file in most popular document reader"
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echo "% less new_file.txt"
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less new_file.txt

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echo "Less is cool, to learn more about it we should read it's manual. But how?"
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echo "% man man, man"
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man man

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echo "Now for the less manual"
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echo "% man less"
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man less

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echo "From the less man page, we learned commands for search up: ?, search down: /, next value: n, and quit: q"
echo "In summary, you can search files by opening them in less but this a slow manual process."

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echo "What do you do if you need to search multiple files for certain text?, grep is how we do this automated searching"
echo "For example, to Search for the word 'Life',  we use: grep [pattern] path"
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echo "% grep Life new_file.txt"
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grep Life new_file.txt

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echo "Now, what if we need to search for the word 'life', but we don't care about the case. -i will ignore case"
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echo "% grep -i life new_file.txt"
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grep -i life new_file.txt

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echo "Want to know how many times the world life occurs in this file?, use count: '-c'"
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echo "% grep -c [pattern] path"
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echo "% grep -c  Life new_file.txt"
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grep -c  Life new_file.txt

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echo "Here is where it gets a little harder."
echo "What if you wanted to know every line of the file that starts with 'Life', in that case we need to learn what the 're' means in grep"
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echo "grep means: globally search a regular expression and print"

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echo "Here are the the minimum aspects of regular expressions you should learn"
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echo ". means any single character"
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echo "* Matches the preceding element zero or more times."
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echo "^ Matches the start of the line."
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echo "$ Matches the end of the line."
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echo "[ ] Matches a single character that is contained within the brackets."
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echo "[^ ] Matches a single character that is not contained within the brackets."

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echo "Examples"

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echo "Lines that start with the word Life"
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echo "% grep ^Life new_file.txt"
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grep ^Life new_file.txt

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echo "Lines that end with the word Life"
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echo "% grep Life$ new_file.txt"
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grep Life$ new_file.txt

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echo "Lines that have ' life '  "
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echo '% grep " life " new_file.txt'
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grep " life " new_file.txt

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echo "lines that containe words that start with 'l'"
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echo '% grep ' l.*' new_file.txt'
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grep ' l.*' new_file.txt

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echo "lines that contain words that that contain a z or a"
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echo '% grep [za] new_file.txt'
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grep [za] new_file.txt

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echo "lines that don't contain a z or an a"
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echo '% grep [^za] new_file.txt'
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grep [^za] new_file.txt

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echo "now lets search a bunch of files, use a file glob instead of a file name. "
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echo "use ? for matching single characters, and * for matching anything"
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echo '% cp new_file.txt another.txt'
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echo '% cp new_file.txt and_another.txt'
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echo '% grep [^za] *.?xt'
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echo 'for more: http://rubular.com/'
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cp new_file.txt another.txt
cp new_file.txt and_another.txt
grep [^za] *.?xt

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echo "we can also use file globbing to just find files"
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echo 'find . -type f -name "*.?xt" 2>/dev/null'
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echo '  ^   that means current directory, it is NOT a regular expression or a file glob in this context.'
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echo '           ^     only return files'
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echo '                     ^ files that start with anything, have a period, then any single letter, then end with xt'
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echo '                             ^  redirect all the errors to null'
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find . -type f -name "*.?xt" 2>/dev/null
#    ^   that means current directory, it is NOT a regular expression or a file glob in this context.
#           ^     only return files
#                      ^ files that start with anything, have a period, then any single letter, then end with xt
#                             ^  redirect all the errors to null

#
# 
# secret bonus material on the find command
#---------------------------------------------
#
# find . -name "*.orig" -exec rm {}\;
#
# and an easier way: find . -name "*.orig" -delete
#
# Use at your Own risk
#
#

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echo "what if you want to search the whole home drectory for tha file?, instead of '.' just just '~' for the root directory "
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echo "this will search all of home directory, return only files that end it .(any single letter)xt"
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echo '% find ~ -type f -name "*.?xt" 2>/dev/null'
find ~ -type f -name "*.?xt" 2>/dev/null
echo "Big search over"

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echo "The whole computer, pass it root:  'find / -type f -name "*.?xt" 2>/dev/null | wc -l'"

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echo "Empty our file, also called clobbering"
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echo '% echo "" > new_file.txt'
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echo "" > new_file.txt

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echo "How man lines are left in the file?"
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echo '% cat new_file.txt | wc -l'
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cat new_file.txt | wc -l

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echo "Clean up our files"
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echo '% rm  new_file.txt'
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echo '% rm  another.txt'
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echo '% rm  and_another.txt'
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rm  new_file.txt
rm  another.txt
rm  and_another.txt

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echo "Thats all folks!"
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echo "And now a Mission Immpossible reference"
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say "I will self destruct in 5 seconds"; for (( i = 5; i > 0; i-- )); do  say $i ; done