bash and Linux CLI Utilities Cheatsheet

This is NOT a first-time learning resource. Some parts are intentionally out of order and kept as.

Resources

References:

Learn X in Y minutes - bash (learnxinyminutes.com)
Learn X in Y minutes - sed (learnxinyminutes.com)

Tutorials:

bash

Basics and I/O

$ ./demo.sh foo bar baz

#!/usr/bin/env bash

set -v    # Print commands as they are run.

echo "$#"   # "3" (number of args)
echo "$@"   # "foo bar baz"

echo "$0"   # "./demo.sh"
echo "$1"   # "foo"
echo "$2"   # "bar"

# Read stdin into new variable $name
echo "What is your name?"
read name
echo "Hello, $name!"

# Read contents of a file into a variable
filecontents=$(cat myfile.txt)
echo "$filecontents"

Variables & Assignment

# Variable assignment must have no space around the `=` character.
my_var1="lmao ayy"
my_var2=$(printf "%s %d\n" "hello" 123)   # my_var3 becomes "hello 123"

# When in doubt, use double-quotes for variable expansion.

echo "$my_var1"      # "lmao ayy"
echo "${#my_var1}"   # "8" (string length)

echo "${my_var1:2:5}"   # "ao ay"
echo "${my_var1: -2}"   # "yy" (the space is required)

echo "${my_var1/ayy/dab}"   # "lmao dab"

other_var="my_var1"
echo "${!other_var}"   # "lmao ayy"

# Default value if empty/nonexistent
echo "${i_dont_exist:-"foo"}"      # "foo"
echo "${i_dont_exist:-$my_var1}"   # "lmao ayy"
echo "${my_var1:-"foo"}"           # "lmao ayy"

##################################################

my_array=(apple banana orange lemon)

echo "${my_array[@]}"        # "apple banana orange lemon"
echo "${#my_array[@]}"       # "4"

echo "${my_array[0]}"        # "apple"
echo "${my_array[1]}"        # "banana"
echo "${my_array[@]:1:2}"    # "banana orange" (same slicing as string)

##################################################

echo {1..10}     # "1 2 3 4 5 6 7 8 9 10"
echo {a..g}      # "a b c d e f g"
#echo {$x..$y}   # CAN'T USE VARIABLES

Structure & Control Flow

echo "first"; echo "second"
echo "always executes" || echo "only executes if first command fails"
echo "always executes" && echo "only executes if first command does not fail"

my_arr=(apple banana orange lemon)
for v in ${my_arr[@]}; do
    echo $v
done

str1="foo"
if [[ $str1 == "bar" ]]; then
    echo "this is true"
else
    echo "this is false"
fi

num1=12
if [[ $str1 != "bar" ]] && [[ $num1 -eq 12 ]]; then
    echo "this is true"
fi

Summary of Basic CLI Utilities

TODO: Whirlwind tour of everything including sed and awk.

sed

TODO: This

awk

TODO: This

Some Common Sysadmin Utilities

TODO: Whirlwind tour of everything including sed and awk.

TODO

TODO: jobs, fg, bg, kill