Crash course on bash
Manual for any command
man find
Change directory
cd folder/
List of available folders and files
ls
- -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 ..
For checking file content
cat file.txt
# Hello world
For checking file content
cat file.txt
# Hello world
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.
To create a file
touche file.txt
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``
Make new directory
mkdir my_folder
To create folder and new folder in it, add -p flag
mkdir -p outter_dir/inner_dir
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/
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
Copy, as with move we could also rename while copying
cp file.txt folder/file.txt
To copy whole folder
cp -R src/* dest/
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
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
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
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
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
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
}
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
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
Check exit status
echo $?
Pause of 5 seconds
sleep 5 # we can add m, h, d for minutes, hours or days