bash memo

I made a script for updating IPv4 of MyDNS.JP with a shell script (MyDNS.jp-v4-Update.sh). , Note the findings at that time

Variable assignment

Substitute without opening a space

hoge="hoge"

NG example

If you open a space and substitute as shown below, you will get angry with not found or command not found.

hoge = "hoge"

Get string length

It seems that it can be taken as a numerical value

${#hoge}

String variable expansion

Put a dollar on your head

echo $hoge

String concatenation

ʻEcho" Moji $ {hoge} Moji "`

Command expansion

Part 1

Enclose in backticks

hoge=`echo "hoge"`

Part 2

Enclose in $ (). Easy to write when nesting

hoge=$(echo "hoge")

Nest sample connecting 1 and 2

For example, the content of ip_res will be something like " 127.0.0.1 200 "

`ip_res=`echo """$(curl inet-ip.info/ip -s -m 10 -w ' %{http_code}')"""



## Get date

`` hoge_date=`date "+%Y/%m/%d %H:%M:%S"` ``  

## if statement

```sh
hoge="hoge"
if [ ${hoge} = "hoge" ]; then
  #Honyara
elif [ 1 -eq 1 ]; then
  #Are comparison operators different for numbers and strings?
else
  #Funyara
fi

function

There seems to be no concept of scope unless explicitly specified


fuga() {
  #Fugarara
}

fuga

Escape sequence with echo

Add the -e option

echo -e "\n"

Reference article

-Operators used in if and while statements in shell scripts (bash) -Note on Bash variable scope

[LINUX] Bash script memo