gistfile1.eclass

#!/bin/bash

################################################## Basic

# this is comment

########### variable (quoting a variable preserves whitequotes)

# USERNAME='lzyy'
# 
# echo ${USERNAME}
# echo ${USERNAME=`whoami`}

########### separator

# echo 'hello'; echo 'world';

########### clear & append to file

# > /tmp/nothing 
# >> /tmp/append
# < /input/file

########### {}

# cat {file1,file2,file3} > file
# cp file11.{txt,backup}

########### []

# if [ -z "$1" ];then
# fi

# if [ "$exp1" -a "$exp2" ];then
# 	...
# fi
# 
# if [ "$exp1" -o "$exp2" ];then
# 	...
# fi

# arr[1] = 'ifeng'
# echo ${arr[1]}

########### xargs and {}

# ls . | xargs -I file cp -r file ../




################################################## Variable

########### undefined variable

# if [ -z "$var" ];then
# 	echo "\$var is NULL"
# fi

########### variable assignment

# a=`echo hello`

########### magic ${...}

# a=5566
# b=${a/55/ss}
# echo $b

# ${#string} # string length

# ${string:position:length}
# ${string:-default} # '-' means default, if you want right index, put brace around
# ${string:(-4)}

# ${string#substring} # deletes shortest match of $substring from front of $string
# ${string##substring} # deletes longest match of $substring from front of $string
# ${string%substring} # backend shortest
# ${string%%substring} # backend longest

# ${string/substring/replacement} # first
# ${string//substring//replacement} # all

########### Arguments passed to the script

# $0, $1, $2 # $0 is script file name
# $# # param num

# if [ -z "$1" ];then
# 	echo "\$1 is empty"
# fi




################################################## Condition && loop

########### if elif else

# if [ ... ]; then
# 	...
# elif
# 	...
# else
# 	...
# fi

########### file test

# -e # file exists
# -f # is a regular file

########### int test

# -eq # equal to
# -ne # not equal
# -gt # greater than
# -lt # less than

########### string test

# = # equal to
# != # not equal to
# < # less than (ascii order)
# > # less than (ascii order)
# -z # string is null
# -n # string is not null

########### while & for loop

# while [ ... ]; do # while read line; do
# 	...
# done
# 
# for item in $var; do # $var is separator by ' '
# 	...
# done




################################################## Function

# func ()
# {
#   local var # if not declare as 'local', it is defined as a global var (like js)
# 	...$1 $2
# }
# 
# func param1 param2 # function call is like bash call

# var="a
# b
# c"
# 
# echo ${#var}

## if you want return val, echo to std

# func()
# {
# 	echo 'hello world';
# }
# 
# return_val=$(func)
# 
# echo ${return_val}




################################################## Date

# date +%j # + start format
# date "+%Y-%m-%d %H:%M:%S"




################################################## Array

# area[11]=15
# area[13]=36
# area[20]='hello'
# 
# area=(hello 1 3)

# echo ${area[11]}
# echo ${area[@]}
# echo ${area[@]:position:length}




################################################## Utils

## internal variables
# export # makes a variable available to all child processes
# wait # Suspend script execution until all jobs running in background have terminated

## useful cmd
# find
# date
# uniq
# head
# tail
# grep
# sort
# sed (sed -i '' -e's/search/replace/g' file)
# awk (awk -F: '{print $2}')
# wc (wc -l / -c)
# tar/gzip/zip
# which/whereis
# diff/patch (patch -p0 xxx.patch)
# basename/dirname
# mktemp
# wget
# rsync (rsync -avz source dest)
# top
# pgrep/pkill
# ps (ps ax)
# watch




################################################## Advanced

########### heredoc

# >test.txt <<EOT
# what
# a
# wonderful
# world
# EOT

########### subshell

# outer='hello outer'
# 
# (
# echo ${outer}
# )