Shell Overview
===
###### tags: `OS / Ubuntu / shell script`
###### tags: `OS`, `Ubuntu`, `linux`, `command`, `shell script`, `sh`, `bash`, `shebang`, `hashband`, `string`, `if-else`, `for-loop`, `makefile`, `指令串接`

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[TOC]

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# Linux: Shell script

## 術語
### bash
[bash (Bourne-Again Shell) ](https://www.796t.com/content/1546346172.html)

### dash
[dash (Debian Almquist Shell)](https://www.796t.com/content/1546346172.html)

### sheband (hashband)
- `#`: hash
- `!`: bang [ʃəˋbæŋ]
- https://tw.dictionary.search.yahoo.com/search?p=bang
- int. 砰！
- vi. 發出砰的一聲；砰砰作響；
- vt. 砰地敲（或推，扔）；猛擊，猛撞；
- shebang 是什麼？
[ChatGPT] shebang（也稱為 hashbang）是一種在腳本文件的第一行使用的特殊註釋語法，用於指定解釋器的路徑。它的格式是以井號（#）開頭，後面跟著一個嘆號（!），然後是解釋器的路徑。在執行腳本時，操作系統會讀取 shebang 行，並使用指定的解釋器來解釋執行該腳本。例如，一個使用 shebang 的 Python 腳本可能會在第一行寫上 #!/usr/bin/python，以指定使用 Python 解釋器來運行該腳本。這樣就可以直接執行腳本文件而無需顯式地調用解釋器。
- 範例1

    #! /bin/bash

- 範例2: `echo_test.sh`

    #! /bin/bash
    echo -e 'a\nb\nc'

    $ sh echo_test.sh
    $ bash echo_test.sh
    $ cdmod +x echo_test.sh; ./echo_test.sh

- 範例3: `echo_test.sh`

    #! /bin/sh
    echo -e 'a\nb\nc'

    $ sh echo_test.sh
    $ bash echo_test.sh
    $ cdmod +x echo_test.sh; ./echo_test.sh

- 參考資料
- [Shell Scripting for Beginners – How to Write Bash Scripts in Linux](https://www.freecodecamp.org/news/shell-scripting-crash-course-how-to-write-bash-scripts-in-linux/)
- [Python 文件頂部的 #!/user/bin/env python 是什麼意思](https://ithelp.ithome.com.tw/articles/10309816)

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<hr>

<br>

## 模式

### 登入 Shell vs. 非登入 Shell
- ### 登入 Shell：
由登入系統時啟動（例如，透過 SSH 或控制台）。
會讀取 `/etc/profile`、`~/.bash_profile`、`~/.bash_login`、`~/.profile` 等配置文件。
- ### 非登入 Shell：
由登入 Shell 或其他程序啟動（例如，您在登入 Shell 中執行 `bash`）。
會讀取 `~/.bashrc` 配置文件。
- ### status 差異
- **登入 Shell：**

        $ shopt
        ...
        login_shell     on
        ...

- **非登入 Shell：**

        $ shopt
        ...
        login_shell     off
        ...

- ### cmd 差異
- **登入 Shell：**

        $ echo $0
        -bash
        $ ps -p $$ -o args=
        -bash

        $ p() { basename "$(pwd)"; }
        -bash: syntax error near unexpected token `('

- **非登入 Shell：**

        $ bash
        $ echo $0
        bash
        $ ps -p $$ -o args=
        bash

        $ p() { basename "$(pwd)"; }
        $ p

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<hr>

<br>

## 入門
- [Shell Scripting for Beginners – How to Write Bash Scripts in Linux](https://www.freecodecamp.org/news/shell-scripting-crash-course-how-to-write-bash-scripts-in-linux/)

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<hr>

<br>

## 特殊變數
### 教學資料
- ### [Shell特殊变量：Shell $0, $#, $*, $@, $?, $$和命令行参数](http://c.biancheng.net/cpp/view/2739.html)
| 变量 | 含义 |
|----|----|
| `$0` | 当前脚本的文件名 |
| `$n` | 传递给脚本或函数的参数。n 是一个数字，表示第几个参数。例如，第一个参数是$1，第二个参数是$2。 |
| `$#` | 传递给脚本或函数的参数个数。 |
| `$*` | 传递给脚本或函数的所有参数。 |
| `$@` | 传递给脚本或函数的所有参数。被双引号(" ")包含时，与 $* 稍有不同，下面将会讲到。 |
| `$?` | 上个命令的退出状态，或函数的返回值。 |
| `$$` | 当前Shell进程ID。对于 Shell 脚本，就是这些脚本所在的进程ID。 |

- :warning: **`$*` 和 `$@` 的区别**
- `$*` 把所有的參數，打包成 1 個，可以說是 all-in-one

- ### [Bash wait Command with Examples](https://phoenixnap.com/kb/bash-wait-command)
| 变量 | 含义 |
|----|----|
| `&` | ampersand sign (and 符號), indicats a background job |
| `$!` | 最後背景程序的 PID |
| `$?` | 最後程序的離開狀態 |

- 比較 `$$` 和 `$!`
- `$$` 是當前 SHELL 程序的 PID
- `$!` 是最後一個背景程序的 PID
- ### [操作 `${@}`](https://stackoverflow.com/questions/1537673)
1. open new file and edit it: vim r.sh:

        echo "params only 2    : ${@:2:1}"
        echo "params 2 and 3   : ${@:2:2}"
        echo "params all from 2: ${@:2:99}"
        echo "params all from 2: ${@:2}"

2. run it:

        $ chmod u+x r.sh
        $ ./r.sh 1 2 3 4 5 6 7 8 9 10

3. the result is:

        params only 2    : 2
        params 2 and 3   : 2 3
        params all from 2: 2 3 4 5 6 7 8 9 10
        params all from 2: 2 3 4 5 6 7 8 9 1

### 實作範例
- `myshell.sh`

    echo "Hello, myshell!"
    echo '----------------------'
    echo "\$@: $@"
    echo "\$*: $*"
    echo "\$#: $#"
    echo "\$0: $0"
    echo "\$1: $1"
    echo "\$2: $2"
    echo "\$3: $3"
    echo "\$4: $4"
    echo "\$5: $5"
    echo "\$?: $?"
    echo "\$$: $$"

    echo '----------------------'
    echo "\${1}: ${1}"
    echo '${1:+"$@"}:' ${1:+"$@"}
    echo '${1:+"$*"}:' ${1:+"$*"}
    echo '${1:+"$#"}:' ${1:+"$#"}

    echo '----------------------'
    echo 'for var in $@'
    for var in $@
    do
      echo "$var"
    done

    echo

    echo 'for var in '"'"'$@'"'"''
    for var in '$@'
    do
      echo "$var"
    done

    echo

    echo 'for var in "$@"'
    for var in "$@"
    do
      echo "$var"
    done

    echo '----------------------'
    echo 'for var in $*'
    for var in $*
    do
      echo "$var"
    done

    echo 

    echo 'for var in '"'"'$*'"'"''
    for var in '$*'
    do
      echo "$var"
    done

    echo 

    echo 'for var in "$*"'
    for var in "$*"
    do
      echo "$var"
    done

- ### 測試1：`sh myshell.sh aa 'bb \" cc' "dd \" ee" ff`

    Hello, myshell!
    ----------------------
    $@: aa bb \" cc dd " ee ff
    $*: aa bb \" cc dd " ee ff
    $#: 4
    $0: myshell.sh
    $1: aa
    $2: bb \" cc
    $3: dd " ee
    $4: ff
    $5: 
    $?: 0
    $$: 3374206
    ----------------------
    ${1}: aa
    ${1:+"$@"}: aa bb \" cc dd " ee ff
    ${1:+"$*"}: aa bb \" cc dd " ee ff
    ${1:+"$#"}: 4
    ----------------------
    for var in $@ <--- 展開不正確
    aa
    bb
    \"
    cc
    dd
    "
    ee
    ff

    for var in '$@'
    $@

    for var in "$@"
    aa
    bb \" cc
    dd " ee
    ff
    ----------------------
    for var in $* <--- 展開不正確
    aa
    bb
    \"
    cc
    dd
    "
    ee
    ff

    for var in '$*'
    $*

    for var in "$*"
    aa bb \" cc dd " ee ff

- :warning: `'$@'` `'$*'` 是純字串
- :warning: `$@` `$*` 正確用法應該是要加雙引號
- :warning: `"$*"` 用途不明
- :warning: 底下有沒有加 `: (colon)`，目前測起來沒有差別

        echo '${1+"$@"}:' ${1+"$@"}
        echo '${1+"$*"}:' ${1+"$*"}
        echo '${1+"$#"}:' ${1+"$#"}

- ### 測試2：`sh myshell.sh`

    Hello, myshell!
    ----------------------
    $@: 
    $*: 
    $#: 0
    $0: myshell.sh
    $1: 
    $2: 
    $3: 
    $4: 
    $5: 
    $?: 0
    $$: 3374612
    ----------------------
    ${1}: 
    ${1:+"$@"}:
    ${1:+"$*"}:
    ${1:+"$#"}:
    ----------------------
    for var in $@

    for var in '$@'
    $@

    for var in "$@"
    ----------------------
    for var in $*

    for var in '$*'
    $*

    for var in "$*"

- ### 測試3：透過 `bash -c ...` 測試 `$@` 和 `$*` 之間的差異
[](https://i.imgur.com/rC7S76P.png)

[](https://i.imgur.com/Upwppe3.png)

- ### 參考資料
- [How to escape single quotes within single quoted strings](https://stackoverflow.com/questions/1250079)
- [${1:+"$@"} in /bin/sh](https://stackoverflow.com/questions/154625/)
- If `$1` exists and is not an empty string, then substitute the quoted list of arguments.
如果 `$1` 存在且不是空字串，則替換成引用的參數清單
- [How to iterate over arguments in a Bash script](https://stackoverflow.com/questions/255898)
- [Add arguments to 'bash -c'](https://unix.stackexchange.com/questions/144514/)

<br>

<hr>

<br>

## 重導參數研究 (forward parameters)
> #dockerfile, forward parameters, forward arguments,

### 實作1
- ### `Dockerfile`

    FROM ubuntu:18.04

    COPY preshell.sh /usr/local/bin/preshell
    RUN chmod +x /usr/local/bin/preshell
    ENTRYPOINT ["preshell"]

    COPY myshell.sh /usr/local/bin/myshell
    RUN chmod +x /usr/local/bin/myshell
    CMD ["bash"]

- ### `preshell.sh`

    #!/bin/bash

    echo 'raw info:'
    echo '---------------------------------'
    echo "command: $@"
    echo "\$0: $0"
    echo "\$1: $1"
    echo "\$2: $2"
    echo "\$3: $3"
    echo "\$4: $4"
    echo "\$5: $5"
    echo "(more, total=$#)"
    echo

    # get the user's script name
    script=$1

    # skip the script name, then get the remaining arguments
    # i.e. preshell.sh echo a b c
    #   => preshell.sh a b c      (where echo is dropped)
    shift

    # escape chars for \ and "  (where \ goes first)
    args=""
    for arg in "$@"
    do
      # replace all occurrences, use ${parameter//pattern/string}:
      arg=${arg//\\/\\\\}
      arg=${arg//\"/\\\"}
      args="$args \"$arg\""
    done

    # pattern: 
    #     sh -c '$0 "$@"' $script $arg1 $arg2 $arg3 ...
    # e.g. 
    #     sh -c '$0 "$@"' echo aa 'bb' "cc" 'dd ee' "ff gg" 'hh'"'"'"ii' "jj'\"kk"
    #     sh -c '$0 "$@"' echo -e "WX\bYZ\tZ\nA"
    # where:
    #  - ' in 'hh'"ii' string needs to be escaped as '""'
    #  - skip_arg0 does nothing
    #  - if you use $0 as script name, you will get preshell.sh instead of $script
    #
    cmd="sh -c '$script "'"$@"'"' skip_arg0 $args"

    echo "\$script: $script"
    echo "\$args: $args"
    echo "\$cmd: $cmd"
    echo ">>>>>>>>>>>"

    echo "\$cmd: $cmd"
    eval $cmd

    echo "<<<<<<<<<<<"
    echo "exiting"
    exit

- `$@` 就是指 args (argument list)，不包含 $0
- ### `myshell.sh`

    #!/bin/sh

    echo "Hello, myshell!"
    echo '----------------------'
    echo "\$@: $@"
    echo "\$*: $*"
    echo "\$#: $#"
    echo "\$0: $0"
    echo "\$1: $1"
    echo "\$2: $2"
    echo "\$3: $3"
    echo "\$4: $4"
    echo "\$5: $5 (more)"
    echo "\$#: $#"
    echo "\$?: $?"
    echo "\$$: $$"

    echo '----------------------'
    echo "\${1}: ${1}"
    echo '${1:+"$@"}:' ${1:+"$@"}
    echo '${1:+"$*"}:' ${1:+"$*"}
    echo '${1:+"$#"}:' ${1:+"$#"}
    echo '${1+"$@"}:' ${1+"$@"}
    echo '${1+"$*"}:' ${1+"$*"}
    echo '${1+"$#"}:' ${1+"$#"}

    echo '----------------------'

    echo 'for var in "$@"'
    for var in "$@"
    do
      echo "$var"
    done

    echo '----------------------'

    echo 'for var in "$*"'
    for var in "$*"
    do
      echo "$var"
    done

- ### 操作流程

    $ docker build -t ubuntu-test:18.04 ./

    $ docker run --rm -it ubuntu-test:18.04 ls -ls

    $ docker run --rm -it ubuntu-test:18.04 myshell aa 'bb' "cc" 'dd ee' "ff gg" 'hh'" ' "' " ii' "jj ' \" kk"

- ### debug 專用
`tmp.sh`

    #!/bin/bash

    script=echo
    echo $@

    args=""
    for arg in "$@"
    do
      # replace all occurrences, use ${parameter//pattern/string}:
      arg=${arg//\\/\\\\}
      arg=${arg//\"/\\\"}
      args="$args \"$arg\""
    done
    echo $args

    cmd="sh -c '$script "'"$@"'"' bash $args"
    echo $cmd
    eval $cmd

執行方式：`$ bash tmp.sh a b c`
只能使用 bash，因為有使用到 find-replace 用法 (sh 無提供)

### 參考資料
- [Add arguments to 'bash -c'](https://unix.stackexchange.com/questions/144514/) :+1: :+1: :100:

    /bin/bash -c 'echo "$0" "$1"' foo bar
    /bin/bash -c 'echo "$@"' bash foo bar
    /usr/bin/env -- "ls" "-l"

執行結果

    foo bar
    foo bar
    (ls -l 略)

若加入 `shift` 指令，則：

    /bin/bash -c 'shift; echo "$0" "$1"' foo bar
    /bin/bash -c 'shift; echo "$@"' bash foo bar

執行結果

    foo
    bar

- [Joining bash arguments into single string with spaces](https://unix.stackexchange.com/questions/197792)

### 實作2 (更簡單)
- [[官方][Docker] ENTRYPOINT](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#entrypoint)

    #!/bin/bash
    set -e

    if [ "$1" = 'postgres' ]; then
        chown -R postgres "$PGDATA"

        if [ -z "$(ls -A "$PGDATA")" ]; then
            gosu postgres initdb
        fi

        exec gosu postgres "$@"
    fi

    exec "$@"

<br>

<hr>

<br>

## 變數範圍
- [Set a parent shell's variable from a subshell](https://stackoverflow.com/questions/15541321/set-a-parent-shells-variable-from-a-subshell)

    a=3
    (a=4)
    echo $a #=3

    a=3
    { a=4;}
    echo $a #=4

- [how to export VARs from a subshell to a parent shell?](https://serverfault.com/questions/37796/how-to-export-vars-from-a-subshell-to-a-parent-shell)

<br>

<hr>

<br>

## 方法參數

### file exist or not exist

if [ -e filename  ]; then echo 'exist'; else echo 'not exist'; fi
# 等效於
if test -e filename; then echo 'exist'; else echo 'not exist'; fi

if [ -f azure-parabricks-test_key.pem ]; then
  echo 'exist'
else
  echo 'NOT exist'
fi

if [ -z azure-parabricks-test_key.pem ]; then
  echo 'NOT exist'
else
  echo 'exist'
fi

- [How to Check if a File or Directory Exists in Bash](https://linuxize.com/post/bash-check-if-file-exists/) :+1: :100:
- [What does "if [ -e $name ]" mean? Where $name is a path to a directory](https://unix.stackexchange.com/questions/127743/)

<br>

### variable exist or not exist
- unset, set (empty, non-rmpty)?
- `${var+x}`: 當 `var` 有任何指派(=)動作，就會有 `x`(字串)
- `${var:+x}`: 當 `var` 有任何指派(=)動作 & 長度大於0，就會有 `x`(字串)
- `[ -z $var ]`: 當 `var` 有任何指派(=)動作 & trim()後長度大於0，就會是 false，其餘為 true
`[ -z ${var} ] && echo echo unset_or_empty || echo not_empty`
- `$ if __condition__; then echo "unset [${p}][${p+HOME}][${p:+HOME}]"; else echo "set [$p][${p+HOME}][${p:+HOME}]"; fi`
- 條件測試：`-z ${p}`

| condition | -z -> true | -z -> false |
| --------- | ---------------- | ----------- |
| unset p | unset [][][] | |
| p= | unset [][HOME][] | |
| p='' | unset [][HOME][] | |
| p="" | unset [][HOME][] | |
| p=' ' | unset [ ][HOME][HOME] | |
| p=" " | unset [ ][HOME][HOME] | |
| p="param" | | set [param][HOME][HOME] |
- 條件測試：`-z ${p+x}`
| condition | -z -> true | -z -> false |
| --------- | ---------------- | ----------- |
| unset p | unset [][][] | |
| p= | | set [][HOME][] |
| p='' | | set [][HOME][] |
| p="" | | set [][HOME][] |
| p=' ' | | set [ ][HOME][HOME] |
| p=" " | | set [ ][HOME][HOME] |
| p="param" | | set [param][HOME][HOME] |
- 條件測試：`-z ${p:+x}`
| condition | -z -> true | -z -> false |
| --------- | ---------------- | ----------- |
| unset p | unset [][][] | |
| p= | unset [][HOME][] | |
| p='' | unset [][HOME][] | |
| p="" | unset [][HOME][] | |
| p=' ' | | set [ ][HOME][HOME] |
| p=" " | | set [ ][HOME][HOME] |
| p="param" | | set [param][HOME][HOME] |

- [How to check if a variable is set in Bash](https://stackoverflow.com/questions/3601515)
正確方式

    if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi

錯誤方式

    if [ -z "$var" ]; then echo "var is blank"; else echo "var is set to '$var'"; fi

- "$var" 無法區分：[1]變數未被設定 [2]變數是空值
> it doesn't distinguish between a variable that is unset and a variable that is set to the empty string.
- [2.6.2 Parameter Expansion](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02)
- [How To Bash Shell Find Out If a Variable Is Empty Or Not](https://www.cyberciti.biz/faq/unix-linux-bash-script-check-if-variable-is-empty/)
> #if-else, 三元運算子

    [[ ! -z "$var" ]] && echo "Not empty" || echo "Empty"

- [Linux Shell指令碼攻略：shell中各種括號()、(())、[]、[[]]、{}的作用](https://codertw.com/%E7%A8%8B%E5%BC%8F%E8%AA%9E%E8%A8%80/544464/)
- 特殊替換
`${var:-string},${var: string},${var:=string},${var:?string}`
- 模式匹配替換
`${var%pattern},${var%%pattern},${var#pattern},${var##pattern}`
- 字串提取和替換
`${var:num},${var:num1:num2},${var/pattern/pattern},${var//pattern/pattern}`

### 教學
- ### [linux 下shell中if的“-e，-d，-f”是什么意思](https://blog.csdn.net/superbfly/article/details/49274889)
文件表达式
`-e filename` 如果 filename存在，则为真
`-d filename` 如果 filename为目录，则为真
`-f filename` 如果 filename为常规文件，则为真
`-L filename` 如果 filename为符号链接，则为真
`-r filename` 如果 filename可读，则为真
`-w filename` 如果 filename可写，则为真
`-x filename` 如果 filename可执行，则为真
`-s filename` 如果文件长度不为0，则为真
`-h filename` 如果文件是软链接，则为真
`filename1 -nt filename2` 如果 filename1比 filename2新，则为真。
`filename1 -ot filename2` 如果 filename1比 filename2旧，则为真。

<br>

<hr>

<br>

## 語法

### if-then-else-fi

h=/home/tj
if [ $h = "/home/tj" ]; then
  echo 'exist'
else
  echo 'not exist'
fi

- 如果沒有 ';' 會有 error
`tmp.sh: 5: tmp.sh: Syntax error: "else" unexpected (expecting "then")`
亦可改成：`then` 切到下一行

    h=/home/tj
    if [ $h = "/home/tj" ]
    then
      echo 'exist'
    else
      echo 'not exist'
    fi

    h=/home/tj
    if [ $h = "/home/tj" ];
    then
      echo 'exist'
    else
      echo 'not exist'
    fi

- [Shell test命令（Shell []）详解，附带所有选项及说明](http://c.biancheng.net/view/2742.html)

<br>

### if-statement
| 條件 | 說明 | 範例結果 |
|--------------------|----|---------|
| `-n "$VAR"` | 判斷 `$VAR` 是否「非空」 | `"abc"` → ✅；`""` → ❌ |
| `-z "$VAR"` | 判斷 `$VAR` 是否「為空」 | `""` → ✅；`"abc"` → ❌ |
| `"$VAR" = "value"` | 判斷是否等於特定值 | `"abc" = "abc"` → ✅ |

| 符號 | 含義 | 推測來源 |
|------|-----------------------|------------------------|
| `-n` | **non-zero length** | `n` = nonempty 或 non-null |
| `-z` | **zero length** | `z` = zero-length |

# 判斷是否有傳 CMD 參數
if [ -n "$(CMD)" ]; then
    echo "你有傳 CMD=$(CMD)"
else
    echo "你沒有傳 CMD"
fi

<br>

<br>

<hr>

<br>

### bash vs sh
- [运行shell脚本时报错"\[\[ : not found"解决方法](https://www.cnblogs.com/han-1034683568/p/7211392.html)
- bash与sh是有区别的，两者是不同的命令，且bash是sh的增强版，而"[[]]"是bash脚本中的命令，因此在执行时，使用sh命令会报错，将sh替换为bash命令即可：

<br>

<hr>

<br>

## 特殊語法

### 槽狀用法 `'basename $(pwd)'`

alias dirname='basename `pwd`'   # case1
alias dirname='basename $(pwd)'  # case2
alias dirname="basename `pwd`"   # case3
alias dirname="basename $(pwd)"  # case4

# case5
dirname() {
    basename $(pwd)
}

- **雙引號**：命令替換在**定義別名時**發生。
- **單引號**：命令替換*不會**在定義或執行別名時發生。
- **建議**：使用函數比別名更靈活，特別是當涉及到命令替換和參數時。

<br>

### 數值計算
- 操作範例

    # 透過 $((運算式))
    $ echo $(((1+2)*3))
    9
    $ echo $((5/3))
    1

    $ s=1
    $ e=12
    $ echo $(( e - s ))
    11
    $ echo $(( ( e - s ) / 10 ))
    1
    $ echo $(( ( e - s ) / 5 ))
    2

- 時間戳記 timestamp

    date && start_time=`date +%s` && echo "start_time:" $start_time
    sleep 12 # do something
    date && end_time=`date +%s` && echo "end_time:" $end_time

    total=$((end_time - start_time))
    time_h=$((total/3600))
    time_m=$(( (total - time_h*3600) / 60 ))
    time_s=$(( total - time_h*3600 - time_m*60 ))
    echo "Total time: ${time_h}h ${time_m}m ${time_s}s"

<br>

<hr>

<br>

## 回傳值
### Unix 訊號
- [[wiki] Unix訊號](https://zh.wikipedia.org/wiki/Unix%E4%BF%A1%E5%8F%B7)

### exited with code ###
- [Question: My batch job exited with code ###. What does that mean?](http://www.bu.edu/tech/files/text/batchcode.txt) :+1:
> 資料來源：[C 語言為什麼是 int main() { ... }](https://blog.moli.rocks/2016/12/15/why-should-main-return-in-c/)
- the system sets the exit code to 128 + \<signal number\>
- 137: 128 + SIGKILL(9)
- [[FreeBSD] preferable exit codes for programs](https://www.freebsd.org/cgi/man.cgi?query=sysexits&apropos=0&sektion=0&manpath=FreeBSD+4.3-RELEASE&format=html)

<br>

### 11 (SIGSEGV)
- Parabricks / pbrun germline: Received signal: 11

<br>

### 137
- **[Docker-compose exit code is 137 when there is no OOM exception](https://stackoverflow.com/questions/59296801/)**
- According to this post, the exit code of 137 can be due to two main issues.
- The container received a docker stop and the app is not gracefully handling SIGTERM
- The container has run out of memory (OOM).
- **[What causes a container to exit with code 137?](https://janetpanic.com/what-causes-a-container-to-exit-with-code-137/)**
- What causes error 137 in Docker
> Error 137 in Docker denotes that the container was ‘KILL’ed by ‘oom-killer’ (Out of Memory). This happens when there isn’t enough memory in the container for running the process.

- How to resolve error 137 in Docker
> So the first option is to identify the cause of this memory usage.
- **[Process finished with exit code 137 in PyCharm](https://stackoverflow.com/questions/43268156)**
- Exit code 137 means that your process was killed by (signal 9) `SIGKILL`

<br>

<hr>

<br>

## 指令串接
## 指令串接/討論
## `;` 與 `&&` 的差異與使用時機
- ### gpt-4o (2025/04/16)
在 Makefile 或 shell 腳本中，`;` 與 `&&` 都可用來串接多個指令，但它們的行為略有不同。

---

### 🧠 差異比較

| 比較項目 | `;` (semicolon) | `&&` (and operator) |
|----------|------------------|----------------------|
| 執行順序 | 逐行執行，不管前面成功或失敗 | **僅在前一行成功時才執行下一行** |
| 錯誤處理 | 不管 exit code，後面仍執行 | 若前一行失敗（exit code ≠ 0），**中止** |
| 常見用途 | 簡單串接，不關心錯誤 | 嚴謹控制流程、防止錯誤後續執行 |

---

### 🔍 範例比較

**使用 `;`（不管前一行成敗）**

    echo hello; false; echo world

輸出：

    hello
    world

即使 `false` 會回傳錯誤（exit code 1），`echo world` 還是執行了。

---

**使用 `&&`（前一行成功才繼續）**

    echo hello && false && echo world

輸出：

    hello

這裡 `false` 失敗了，導致 `echo world` 不會執行。

---

### ✅ 在 Makefile 中的應用

你原本的程式碼如下：

    run-app:
        export RUN_MODE=$(RUN_MODE); \
        export SERVER_URL=$(SERVER_URL); \
        export SHOW_SWAGGER=$(SHOW_SWAGGER); \
        export SERVER_PORT=$(SERVER_PORT); \
        $(IMAGE_DIR)/entrypoint.sh

因為你只是要「設定一連串環境變數後，執行一個腳本」，用 `;` 是可以接受的，也比較常見。
但如果你希望當某個 `export` 失敗就中止，那可以改用 `&&`：

    run-app:
        export RUN_MODE=$(RUN_MODE) && \
        export SERVER_URL=$(SERVER_URL) && \
        export SHOW_SWAGGER=$(SHOW_SWAGGER) && \
        export SERVER_PORT=$(SERVER_PORT) && \
        $(IMAGE_DIR)/entrypoint.sh

不過實際上 `export` 幾乎不會失敗（除非語法錯），所以 `;` 就夠用了。

---

### ✅ 若想更嚴謹控制流程（可選）

可以改用 `&&`，讓任一 export 失敗時就終止流程：

    run-app:
        export RUN_MODE=$(RUN_MODE) && \
        export SERVER_URL=$(SERVER_URL) && \
        export SHOW_SWAGGER=$(SHOW_SWAGGER) && \
        export SERVER_PORT=$(SERVER_PORT) && \
        $(IMAGE_DIR)/entrypoint.sh

---

### ✅ 更簡潔寫法（推薦）

直接將變數寫在同一行執行：

    run-app:
        RUN_MODE=$(RUN_MODE) SERVER_URL=$(SERVER_URL) \
        SHOW_SWAGGER=$(SHOW_SWAGGER) SERVER_PORT=$(SERVER_PORT) \
        $(IMAGE_DIR)/entrypoint.sh

這樣會在 **同一個 shell 環境中執行**，不需逐行 export，簡潔有效。

<br>

<hr>

<br>

## 特殊操作
### eval
使用 **單引號** 或 **雙引號** 皆可

cmd='echo pid=$$'
eval $cmd

cmd="echo pid=$$"
eval $cmd

執行結果

pid=862639

- [Run a string as a command within a Bash script](https://stackoverflow.com/questions/2355148/)

<br>

### shift
- [How do I forward parameters to other command in bash script?](https://stackoverflow.com/a/1537687/4359712)
`shifttest.sh`:

    #!/bin/bash
    echo $1
    shift
    echo $1 $2

`shifttest.sh 1 2 3` produces

    1
    2 3

- If you forward the arguments as `$1` without quoting them as `"$1"`, then the shell will perform word splitting, so e.g. `foo bar` will be forwarded as `foo` and `bar` separately.

- [shell: "can't shift that many" error](https://superuser.com/questions/897148/)
> 因為沒有多餘的參數可以讓你 shift

    #tmp.sh
    echo '$@: '"$@"
    echo "\$#: $#"
    shift
    echo '$@: '"$@"

執行結果：

    $ sh tmp.sh 
    $@: 
    $#: 0
    tmp.sh: 3: shift: can't shift that many

    $ sh tmp.sh 1
    $@: 1
    $#: 1
    $@: 

    $ sh tmp.sh 1 2 3
    $@: 1 2 3
    $#: 3
    $@: 2 3

解決辦法：

    echo '$@: '"$@"
    echo "\$#: $#"
    if [ $# -gt 0 ]; then
      echo "do shift"
      shift
    fi
    echo '$@: '"$@"

<br>

### 字串 string
- ### [Replace one substring for another string in shell script](https://stackoverflow.com/questions/13210880)
- ### 字串串接

    x=123
    y=abc
    z=$x$y  # z=${x}y, z=$x${y}, z=${x}${y}
    echo $z

- [How to concatenate string variables in Bash](https://stackoverflow.com/questions/4181703)
- ### 子字串
> `${變數:起始索引:長度}`

    x=0123456789
    echo '${x:0:3}: '${x:0:3}      # 012
    echo '${x:7:3}: '${x:7:3}      # 789
    echo '${x:5:100}: '${x:5:100}  # 56789

去頭
> `#$%` 的 `#`
> 語法：`${x` + `#` + `*`(萬用字元) + `尋找字元` + `}`

    x=0123456789
    echo ${x#*3}  # 砍掉 0123，只留 456789
    
    x=0011223344
    echo ${x#*3}  # 砍掉 0011223 (not greedy)，只留  344
    echo ${x##*3} # 砍掉 00112233 (greedy)，只留 44

去尾
> `#$%` 的 `%`
> 語法：`${x` + `%` + `*`(萬用字元) + `尋找字元` + `}`

    x=0123456789
    echo ${x%3*}  # 砍掉 3456789，只留 012
    
    x=0011223344
    echo ${x%3*}  # 砍掉 344 (not greedy)，只留 0011223

- [Extract substring in Bash](https://stackoverflow.com/questions/428109)

- ### 格式化

    x=123
    printf "%06d\n" $x
    printf "%6d\n" $x
    printf "%-6d\n" $x


    x=0123456789
    printf "%.0s\n" $x
    printf "%.2s\n" $x  # 01
    printf "%.5s\n" $x  # 01234

- [Linux printf command](https://www.computerhope.com/unix/uprintf.htm)

- ### 路徑處理
> 見「子字串」處理

- 取出檔案名稱：`${X##*/}`
- `#` 表示從前面開始找
- `#` 第二個`#`表示貪婪
- `*` 表示從前面開始吃掉任意字元，直到 `/` (最後一個，後面已經沒有 `/`)
- 取出當前路徑：`${X%/*}`
- `%` 表示從後面開始找
- `*` 表示從後面開始吃掉任意字元，直到 `/` (後面數來第一個，不貪婪)
- 完整範例

        X=/home/tj/Downloads/docker/Dockerfile
        echo "檔案名稱：${X##*/}"
        echo "當前路徑：${X%/*}"
        echo "當前路徑：${0}"

執行結果：

        檔案名稱：Dockerfile
        當前路徑：/home/tj/Downloads/docker
        當前路徑：bash

- 參考資料
- [bash - how to find current shell command](https://stackoverflow.com/a/5077898/4359712)
- ### 字串比較

    if [ $h = "/home/tj" ]; then
      echo "case1:$h"
    else
      echo "case2"
    fi

- 會有 error
`tmp.sh: 3: [: =: unexpected operator`
- 解決方法：要加雙引號

        if [ "$h" = "/home/tj" ]; then
          echo "case1:$h"
        else
          echo "case2"
        fi

- [shell腳本報錯："[: =: unary operator expected"](https://www.796t.com/content/1507882933.html)
- 究其原因，是因為如果變量STATUS值為空，那麽就成了 [ = "OK"] ，顯然 [ 和 "OK" 不相等並且缺少了 [ 符號，所以報了這樣的錯誤。
- 其他參考資料
- [Compare a string using sh shell]()

<br>

<hr>

<br>

## 注意事項
### 傳遞環境變數
傳遞環境變數，需以雙引號傳遞，不能用單引號

$ python test.py --PATH='$HOME'    <--- 失敗
['test.py', '--PATH=$HOME']

$ python test.py --PATH='${HOME}'  <--- 失敗
['test.py', '--PATH=${HOME}']

$ python test.py --PATH="$HOME"
['test.py', '--PATH=/home/tj']

$ python test.py --PATH="${HOME}"
['test.py', '--PATH=/home/tj']

<br>

<hr>

<br>

## 完整教學
- [[ITREAD] Shell 教程](https://www.itread01.com/study/linux-shell.html)
- [[鳥哥] 第十二章、學習 Shell Scripts](https://linux.vbird.org/linux_basic/centos7/0340bashshell-scripts.php)

<br>

<hr>

<br>

# Linux: Makefile
## 變數範圍
- [Makefile 語法簡介](https://sites.google.com/site/mymakefile/makefile-yu-fa-jian-jie) :+1: :100:
- [How to abort makefile if variable not set?](https://stackoverflow.com/questions/10858261/)

## API
- [Append date and time to an environment variable in linux makefile](https://stackoverflow.com/questions/1859113)

    $(shell operation)

    LOGPATH = logs
    LOGFILE = $(LOGPATH)/$(shell date --iso=seconds)

    test_logfile:
        echo $(LOGFILE)
        sleep 2s
        echo $(LOGFILE)

<br>

{%hackmd vaaMgNRPS4KGJDSFG0ZE0w %}