My Notes

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|  _ \ / _` / __| '_ \ 
| |_) | (_| \__ \ | | |
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Handling Named Arguments

A neat trick is to use the boolean variables to make a certain part of the script print or not print. Or even better a particular command to execute or not, can we extend it even more? ofcourse!

Example Script:

#!/bin/bash
deploy=false
uglify=false

while (( $# > 1 )); do case $1 in
    --deploy) deploy="$2";;
    --uglify) uglify="$2";;
    *) break;
esac;
shift 2
done

$deploy && echo "will deploy .... deploy = $deploy"
$uglify && echo "will uglify .... uglify = $uglify"

The best part is when udlify is false, the entire statement wont be printed!

What we learn: 1) using while loop (._.) I am embarassed to accept but i didnt knew this is how you create a while loop in bash. 2) $# is for arguments, which was known to me. 3) I still dont know whats shift 2 in bash, will check

[akuma@shiro ~]$ help shift
    shift: shift [n]
    Shift positional parameters.
    
    Rename the positional parameters $N+1,$N+2 ... to $1,$2 ...  If N is
    not given, it is assumed to be 1.
    
    Exit Status:
    Returns success unless N is negative or greater than $#.

So basically thanks to shift 2 we were able to use that to accep uglify as a sysarg variable too 4) Curious use of && :P

List files without using “ls”

This is new stuff!!

# files and directories
printf "%s\n" *
# only directories
printf "%s\n" */
# only particular type of files
printf "%s\n" *.{gif,png,jpg}

To capture a list of files into a variable
```
files = ( * )
for i in "${files[@]}";do
  echo "$file"
done
```
this is better than using ls in for loop which can be dangerous and very heavy.
Using heredoc

If you dont have a file editor, you might not need it :P

─❯ cat <<__X >file
heredoc> pewpew
heredoc> I am using a here doc to write this
heredoc> watashi wa sugoy desu!
heredoc> pewpew 
heredoc> __X

─❯ cat file
   1   │ pewpew
   2   │ I am using a here doc to write this
   3   │ watashi wa sugoy desu!
   4   │ pewpew 

Catting gziped file to one larger file

echo "hi" > hello
echo "bye" > bye
gzip hello
gzip bye
cat hello.gz bye.gz > greetings,gz

# This is ofc inefficient 

Playing with daemon files

#!/bin/bash
if [[ ! -e /tmp/test.py.pid ]]; then   # Check if the file already exists
 python test.py &                   #+and if so do not run another process.
 echo $! > /tmp/test.py.pid
else
 echo -n "ERROR: The process is already running with pid "
 cat /tmp/test.py.pid
 echo
fi

This will be a great help with kunst and ncmpcpp albumart

Mkfifo alright so basically most of the time using
```
cat pew.tmp | grep "lmao"
```
works, and its alright, we can also do
```
curl pewpew.go > tempFile && cat tempFile | grep -v "kek" > lol
```
this works perfectly but it has a problem, the problem of beign deleted. What if someone who doesnt understands whats going on deletes the tempfile, it will simply break lol which is not good. hence we have this:
```
mkfifo mypipe 
echo "hi" > mypipe
cat < mypipe
```
Redirection to network address bash treats /dev/{udp|tcp}/host/port as special file, which allows network communications.
```
execv 3</dev/tcp/www.google.com/80
printf 'GET / HTTP/1.0\r\n\r\n' >&3
cat <&3
```
Control structures for bash

File Operators            Details
-e "$file"                Returns true if the file exists.
-d "$file"                Returns true if the file exists and is a directory
-f "$file"                Returns true if the file exists and is a regular file
-h "$file"                Returns true if the file exists and is a symbolic link

String Comparators        Details
-z "$str"                 True if length of string is zero
-n "$str                  True if length of string is non-zero
"$str" = "$str2"          True if string $str is equal to string $str2. Not best for integers. It may work but will be inconsitent.
"$str" != "$str2"         True if the strings are not equal

Integer Comparators       Details
"$int1" -eq "$int2"       True if the integers are equal
"$int1" -ne "$int2"       True if the integers are not equals
"$int1" -gt "$int2"       True if int1 is greater than int 2
"$int1" -ge "$int2"       True if int1 is greater than or equal to int2
"$int1" -lt "$int2"       True if int1 is less than int 2
"$int1" -le "$int2"       True if int1 is less than or equal to int2