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Read - Takes Input, '$' sign for variables.
```
read name
echo ("Welcome $name")
```

For Loops: Have two braces for Math Ops (())

for ((i = 1; i <= 100; i+=2))
do
    $i
done

While Loop Structure - do, (stuff), done
We use " | bc" for math operations.
```
echo("5+3") | bc
```

Conditionals : if, elif, else, fi

read input

if [ $input == "y" ] || [ $input == "Y" ]; then 
    echo "YES"
else 
    echo "NO"
fi

grep : Will search and print matching.

grep -iwE "the|that|then|those" 

# i - To search case-insensitive. 
# w - To ignore case. 
# E - To compare as an extended regex, to allow use of "|"

grep -v "that" 
# v - Will show invert of what you're searching.

7. sed : To replace.

sed 's/the /this /1'
#Space to avoid words like "therefore"

sed -e 's/thy/your/ig' -e 's/Thy/Your/ig' -e 's/tHy/YouR/ig'
#To replace mutliple words with one
# -e is for editing

sed -e 's/thy/{&}/gi'
#Make it highlight in curly braces. 

sed -e 's/([0-9]+) ([0-9]+) ([0-9]+) ([0-9]+)/\4 \3 \2 \1/' 
#Back-Refrencing. 
#E - for extended regular expression

awk - For comparision and parsing.

awk '{ if ($4 == "") print "Not all scores are available for "$1}'
Variable out of the "". 

awk '{ if (($2 >= 50) && ($3 >= 50) && ($4 >=50)) {print $1" : Pass"} else {print $1" : Fail"}}'


awk '{
total = ($2 + $3 + $4)/3
if (total >= 50 && total< 60)
    print $1,$2,$3,$4, ": C"
else if (total >= 60 && total < 80)
    print $1,$2,$3,$4, ": B"
else if (total >= 80)
    print $1,$2,$3,$4, ": A" 
else 
    print $1,$2,$3,$4, ": FAIL" }'


awk '
    BEGIN {count=0}

    {
        printf "%s %d %d %d", $1, $2, $3, $4
        count++;
        if (count%2 == 0)
            printf "\n"  
        else
            printf ";"
    }
'

Arrays:

while read country
do
    countries=("${countries[@]}" "$country")
done
echo "${countries[@]}"
# First one is array, second one is element being added to array. 


while read country
do 
    countries+=($country)
done
echo "${countries[@]:3:5}"
#Sliced

while read country
do 
    if [[ "$country" != *a* && "$country" != *A* ]]; then
        countries+=("$country")
    fi
done
echo "${countries[@]}"
# Filterting on the basis of letter. 

while read line
do
    elements+=(i)
done 
echo ${#elements[@]}
# counts - "#"

Cut

while read lines
do
    echo "$lines" | cut -c3
done
# Cut a specifc character. 

while read lines
do
    echo "$lines" | cut -c 2,7
done
# Cut multiple characters. 

while read lines
do
    echo "$lines" | cut -c 2-7
done
# Cut a range of charavters. 

while read lines 
do 
    echo "$lines" | cut -d $'\t' -f 1-3
done
# -d : only takes one character so use 'X'

while read lines 
do 
    echo $lines | cut -c 13-
done
# Print from X character to the end. 

while read line
do
    echo "${line}" | cut -d ' ' -f 4
done
# 4th Word, delimeter is ' '.

Head and Tail:

head -n 20 
# For first 20 lines of text. 

head -c 20 
# For first 20 characters of text. 

head -n 22 | tail -n +12
# First 22 characters && Prints from 12th to last (22nd Character)

tr and sort : tr replaces, sort sorts (lol)

tail -n 20
# Last 20 lines.

tr '()' '[]'
# Replace. 

tr -d "(a-z)"
# Delete all lower-case characters. 

tr -s ' '
# Squeezes spaces.

sort -f
# Sorts in alphabetical order, -f ignore case. 

sort -r
# Sorts in reverse alphabetical order. 

sort -n 
# Sorts in numerically ascending order. 

sort -n -r
# Sorts in numerically descending order. 

sort -r -n -k 2 -t $'\t'
# -r : For reverse order 
# -n : numerical sort 
# -k: column ordering 
# -t : tab separted indicator

Uniq:

    uniq
    # Eliminates repetitions. 

    uniq -c 
    # Counts the repitions.

Paste:

paste -d'\t' -s
# '-s' tells the command to write everything sequentially in one line. 

paste -s -d ';'
# Pastes with a delimeter specified.

Last Updated: 2023-03-23 ; Contributors: Fir121

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