WebSys Notes.md

Bash

Printing

# concatinate
cat file.txt

# head
head -n[no of lines] file.txt

# tail
tail -n[no of lines] file.txt

Counting

wc file.txt

# w/o filename
cat file.txt | wc

Listing

• -a - all files
• -l - file permissions
• -t - order by modification time descending
• -S - order by size descending
• -r - reverse order

Grep/Regex

• \s - Whitespace
• \d - digit
• \x - hex digit
• \o - octal
• \h - head of word character ([A-Za-z_])
• \p - printable character
• \w - word character
• \a - alphabetic
• \l - lowercase
• \u - uppercase
• ^ - start of string/line
• $ - end of string/line

Columns

cut -f[field number] -d[delimiter]

awk -F[delimiter] '{print $1 $2 $3 "you can join strings in here too!" }'

If/Else

if [[ "$aaa" = bbb ]]; then
  ...
elif [[ "$aaa" = ccc ]]; then
  ...
else
  ...
fi

Math

# definition
stringed_number=$(( 1 + 4 ))

# if statements
if [ $(( $a % 4 )) -eq 0 ]; then                                
  ...
fi

Commands

# store output into var
output=$(echo  "hi")

Arguments

# number of arguments
$#

# array of arguments
#@

# string of all arguments concatinated
#*

Permissions

whoami

# all groups
id -g

# my groups
id -G

# my group names

id -Gn

• u - user
• g - group
• o - others
• r - read
• w - write
• x - execute

Redirection

• 1 - stdout
• 2 - stderr

# redirection

1>&2

2>&1

# etc..

Loops

while [[ true ]]; do
  ...
done

# you can also use ((i=1;i<=5;i++))
for i in 1 2 3 4; do
    ...
done

Vim

Substitution

# global
:s/foo/bar/g

# on every line globally
:%s/foo/bar/g

Goto Line

:[line number]

# EOF
:$

Insert

• I - BOL
• i - left of cursor
• A - EOL
• a - right of cursor

Delete

• x - at cursor
• D - cursor to EOL
• dd - line
• d[n]d - n lines
• dw - word
• d[n]w - n words
• dG - cursor to EOF
• d[n]G - cursor to line n

Marking

m[letter]
'[letter]