bash-basics

Crash course on bash

man

Manual for any command

man find

cd

Change directory

cd folder/

ls

List of available folders and files

ls

flags

• -l More detailed list

ls -l
# -rw-r--r-- 1 nino8 197609     0 Jul 29 11:52 file.txt

First character is shows us if it is directory (d) or file (-), other flags are permissions. Then we see user, group and created or modified date.

• -a To see hidden files and folder

ls -a
# . .. Some_folder file.txt

. and .. are special folder, they mean current directory and parent directory. So to go up one level you can write cd ..

cat

For checking file content

cat file.txt
# Hello world

cat

For checking file content

cat file.txt
# Hello world

less

Similar like cat, but better tool for file checking. First you only see file content and not previous command, secondly you can navigate more easily (g - beginning of file, shift g - end of file), you can search text with /search_term. Btw, q is for quitting less program.

less file.txt

.

Open current directory. It can be useful for hidden files like .git . .git

. somefile.js - will open with default program for that extension. We can select program to open it with . somefile.js TextEdit. Can be useful for files without ext or without default one.

touch

To create a file

touche file.txt

echo

Something like print or console.log for bash

echo "Hello world"

We could use it to put text in a file echo 'Some sentence I want to save' > file.txt. If we do it multiple times, it will override previous text, so to append we use >> ```echo 'New sentence' >> file.txt``

mkdir

Make new directory

mkdir my_folder

To create folder and new folder in it, add -p flag

mkdir -p outter_dir/inner_dir

rm

Remove folder or file

rm file.txt

To delete folder and its content add recursive flag

rm -r folder/

If you don't want conformation message and error warning if file doesn't exist add -f flag

rm -rf folder/

mv

Move files and folders, but it also can be used for renames

mv target.txt desination_folder/target.txt

Rename while moving

mv target.txt desination_folder/renamed_target.txt

Just rename

mv file.txt renamed_file.txt

cp

Copy, as with move we could also rename while copying

cp file.txt folder/file.txt

To copy whole folder

cp -R src/* dest/

find

To find files and folders a) To find all txt files in my_folder, we would write

find my_folder/ -name "*.txt" # btw, this is not regex

b) For case insensitive search use -iname flag

find my_folder/ -iname "*.txt"

c) To find all folders in current directory

find . -type d

d) We can combine b) and c) to find all folder named text

find . type d -iname "text"

d) We could combine it with delete flag to delete what we found

find . type d -iname "text" -delete

e) To run some operation on found files, like run imaginary encrypt on each txt file in my_important_folder

find my_important_folder/ -iname "*.txt" -exec encrypt

grep

Find search term in files, every outputed line will be one search match a) Find version in lodash package

grep "version" node_modules/lodash/package.json

b) We can search multiple files

grep "version" node_modules/**/*.json

c) To colorize match, --color flag

grep --color "version" node_modules/**/*.json

d) To output two lines before and after found search term, we have context flag -C

grep -C 2 "term" file.txt

e) Use regex with -e

grep -e "[0-9]" file.tx

curl

Output http response

curl www.google.com

a) To include headers use -i flag

curl -i www.google.com

b) By default curl won't follow redirect, if we want that we use L flag

curl -L www.google.com

c) To include headers -H flag

curl -H "Authorization: Bearer 34151534" localhost:8000/api/auth

d) To change http verb -X flag

curl -X POST -H "Content-Type: application/json" -d '{"name": "John"}' http://example.com/api/user
# d is for body

e) To output to a file -o flag

curl -il www.example.com/ -o file.txt

f) To parse json output we could pipe it to some program, like globally installed node package jsome

curl www.site.com | jsome

Scripting

a) To init JS project

touch init-js.sh
echo "Initializing JS project at $(pwd)" # pwd - is current working directory
git init
npm init -y # create package.json with all defaults
mkdir src
touch src/index.js
code . # to open in VS Code

Save file and then run with .init-js.sh If you get persmission denied, with ls -l check first four flags -rw- 1. flag is file or director, then user permission, 2. read, 3. write and 4. execute. if 4th flag is - you don't have execute permission. This are default permissions settings. To change that write chmod u+x script.sh to add to the user execute permission. Now flags should be -rwx

If we want to execute this script from anywhere we must use $PATH variable. Type echo $PATH to see all folders where shell is looking for executables. To see from where node executable is rantype which node To put our file in PATH cp init-js.sh /use/local/bin/init-js Test it with which init-js

Variables

my_var=12345 # Don't use spaces
echo $my_var

Variables are scoped per script.

To export my_var to be accessible outside of script

export my_var

To unset variable

unset my_var

To see all bash global variables

env

Common global var is USER, to reference it echo $USER

Script to clone a local branch from to temp folder

touch clone-to-temp.sh

temp=$(mktemp -d)
git clone --branch $1 $PWD $temp
echo "branch $1 was cloned to $temp folder"
# we can now run some test or task here...

chmod u+x clone-to-temp.sh

#test it with .clone-to-temp.sh new-temp-branch

Functions

greet() {
  echo "Hello world"
}

greet # invoking the function

Passing a var to function is like a script

greet() {
  echo "Hello $1"
}

greet "John"

We can save output

greet() {
  echo "Hello $1"
}

saved_greeting = $(greet "John") # saved_greeting will be variable with "Hello John" value
# if we had more than one echo command, both would be saved in var

We have global and local vars

global_var = 123

greeting() {
  local_var = 456 # accessible only inside this function
}

Conditionals

E.g. Print USER if it John, else print false

if [[ $USER = 'John' ]]; then # not equal sign !=
  echo $USER
else
  echo "false"
fi

We can use && and ||

[[ $USER = 'John' ]] && echo $USER || echo "false

Piping

To see all chrome running processes in less program

ps ax | grep Chrome | less # ps ax to see all running processes

Gzip file.txt and show bytes

gzip -9 | wc -c # 9 is max compression, wc without c flag is for word count

This is outputed in memory, so new file is not created.

To output to file

ls > ls.txt # >> to append

Other

Check exit status

echo $?

Pause of 5 seconds

sleep 5 # we can add m, h, d for minutes, hours or days