frequently used

I hate bash.

I don’t use it frequently enough to have all the stuffs printed in my brain. And everytime I do, I need to google the very basic things.

So fuck it, I’ll learn this once and for all.

# variables

assign values with default

FOO="${VARIABLE:-default}"
# FOO will be assigned 'default' value if VARIABLE not set or null.
# The value of VARIABLE remains untouched.

FOO="${VARIABLE:=default}"
# If VARIABLE not set or null, set its value to 'default'. 
# Then that value will be assigned to FOO

https://stackoverflow.com/questions/2013547/assigning-default-values-to-shell-variables-with-a-single-command-in-bash

# control flows

# functions

# snippets

test if file / directory (doesn’t) exsits

if test -f "$FILE"; then
if [! -f "$FILE"]; then

if test -d "$DIR"; then
if [! -d "$DIR"]; then

# MISC

https://linuxize.com/post/bash-check-if-file-exists/

file test operators

-b FILE - True if the FILE exists and is a special block file.
-c FILE - True if the FILE exists and is a special character file.
-d FILE - True if the FILE exists and is a directory.
-e FILE - True if the FILE exists and is a file, regardless of type (node,
          directory, socket, etc.).
-f FILE - True if the FILE exists and is a regular file (not a directory or
          device).
-G FILE - True if the FILE exists and has the same group as the user running the
          command.
-h FILE - True if the FILE exists and is a symbolic link.
-g FILE - True if the FILE exists and has set-group-id (sgid) flag set.
-k FILE - True if the FILE exists and has a sticky bit flag set.
-L FILE - True if the FILE exists and is a symbolic link.
-O FILE - True if the FILE exists and is owned by the user running the command.
-p FILE - True if the FILE exists and is a pipe.
-r FILE - True if the FILE exists and is readable.
-S FILE - True if the FILE exists and is a socket.
-s FILE - True if the FILE exists and has nonzero size.
-u FILE - True if the FILE exists and set-user-id (suid) flag is set.
-w FILE - True if the FILE exists and is writable.
-x FILE - True if the FILE exists and is executable.