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update(linux-bash): string expansion and array
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issue #104
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@sabertazimi
sabertazimi committed Nov 20, 2018
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245 changes: 235 additions & 10 deletions programming/linux/linuxBasicNotes.md
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Original file line number Diff line number Diff line change
Expand Up @@ -138,7 +138,8 @@
- [case语句](#case语句)
- [for语句](#for语句)
- [while语句与until语句](#while语句与until语句)
- [函数](#函数)
- [Bash Array](#bash-array)
- [Bash Function](#bash-function)
- [Bash IO](#bash-io)
- [信号](#信号)
- [Bash Debugging](#bash-debugging)
Expand Down Expand Up @@ -960,6 +961,46 @@ if [ "$?" -ne "0" ];then
fi
```

每次 shift 命令执行的时候，变量 $2 的值会移动到变量 $1 中，变量 $3 的值会移动到变量 $2 中.
变量 $# 的值也会相应的减1

```bash
#!/bin/bash
# posit-param2: script to display all arguments
count=1
while [[ $# -gt 0 ]]; do
echo "Argument $count = $1"
count=$((count + 1))
shift
done
```

```bash
usage () {
echo "$PROGNAME: usage: $PROGNAME [-f file | -i]"
return
}
# process command line options
interactive=
filename=
while [[ -n $1 ]]; do
case $1 in
-f | --file) shift
filename=$1
;;
-i | --interactive) interactive=1
;;
-h | --help) usage
exit
;;
*) usage >&2
exit 1
;;
esac
shift
done
```

#### 环境变量

- /etc/profile.d/*.sh
Expand All @@ -983,9 +1024,9 @@ fi

### Bash Expansions

- $(()) or $[]: arithmetic expansion
- `$(())` or `$[]`: arithmetic expansion

一般地, 将数值运算用 (()) [[]] 或 $(()) 括起, 可以确保变量不会被识别为 string
一般地, 将数值运算用 `(())` `[[]]` 或 `$(())` 括起, 可以确保变量不会被识别为 string

```bash
read x
Expand All @@ -1010,8 +1051,8 @@ then
fi
```

- [[ xxx ]]: condition
- (( xxx )): arithemetic condition
- `[[ xxx ]]`: condition
- `(( xxx ))`: arithemetic condition

|operator|function|
|:-----------|:-----------|
Expand Down Expand Up @@ -1042,6 +1083,55 @@ echo a{A{1,2},B{3,4}}b
aA1b aA2b aB3b aB4b
```

- `${}`: string expansion
- `${parameter:-word}`: 若 parameter 没有设置（例如，不存在）或者为空，展开结果是 word 的值。
若 parameter 不为空，则展开结果是 parameter 的值
- `${parameter:+word}`: 若 parameter 没有设置或为空，展开结果为空。
若 parameter 不为空， 展开结果是 word 的值会替换掉 parameter 的值
- `${parameter:=word}`: 若 parameter 没有设置或为空，展开结果是 word 的值。
另外，word 的值会赋值给 parameter。
若 parameter 不为空，展开结果是 parameter 的值
- `${parameter:?word}`: 若 parameter 没有设置或为空，这种展开导致脚本带有错误退出，
并且 word 的内容会发送到标准错误。
若 parameter 不为空， 展开结果是 parameter 的值
- `${!prefix*}` `${!prefix@}`: 这种展开会返回以 prefix 开头的已有变量名
- `${#parameter}`: 展开成由 parameter 所包含的字符串的长度
- `${parameter:offset}` `${parameter:offset:length}`: 提取一部分字符
- `${parameter,,}` 把 parameter 的值全部展开成小写字母
- `${parameter,}` 仅仅把 parameter 的第一个字符展开成小写字母
- `${parameter^^}` 把 parameter 的值全部转换成大写字母
- `${parameter^}` 仅仅把 parameter 的第一个字符转换成大写字母
- `${parameter#pattern}` `${parameter##pattern}`,
`${parameter%pattern}` `${parameter%%pattern}`: 从 paramter 所包含的字符串中清除开头/末尾一部分文本
- `${parameter/pattern/string}`, `${parameter//pattern/string}`,
`${parameter/#pattern/string}`, `${parameter/%pattern/string}`: replace

```bash
foo=file.txt.zip
echo ${foo#*.}
txt.zip
echo ${foo##*.}
zip

foo=file.txt.zip
echo ${foo%.*}
file.txt
echo ${foo%%.*}
file
```

```bash
foo=JPG.JPG
echo ${foo/JPG/jpg}
jpg.JPG
echo ${foo//JPG/jpg}
jpg.jpg
echo ${foo/#JPG/jpg}
jpg.JPG
echo ${foo/%JPG/jpg}
JPG.jpg
```

- $(): command result
- "": allow expansions string
- '': disallow expansions string
Expand Down Expand Up @@ -1089,6 +1179,105 @@ case $变量名 in
esac
```

|case pattern|function|
|:-----|:-----------------------------------------|
|`a)`|Matches if word equals "a"|
|`[[:alpha:]])`|Matches if word is a single alphabetic character|
|`???)`|Matches if word is exactly three characters long|
|`*.txt)|Matches if word ends with the characters “.txt”|
|`*)`|Matches any value of word|

```bash
#!/bin/bash
# case-menu: a menu driven system information program
clear
echo "
Please Select:
1. Display System Information
2. Display Disk Space
3. Display Home Space Utilization
0. Quit
"
read -p "Enter selection [0-3] > "
case $REPLY in
0) echo "Program terminated."
exit
;;
1) echo "Hostname: $HOSTNAME"
uptime
;;
2) df -h
;;
3) if [[ $(id -u) -eq 0 ]]; then
echo "Home Space Utilization (All Users)"
du -sh /home/*
else
echo "Home Space Utilization ($USER)"
du -sh $HOME
fi
;;
*) echo "Invalid entry" >&2
exit 1
;;
esac
```

or case pattern

```bash
#!/bin/bash
# case-menu: a menu driven system information program
clear
echo "
Please Select:
A. Display System Information
B. Display Disk Space
C. Display Home Space Utilization
Q. Quit
"
read -p "Enter selection [A, B, C or Q] > "
case $REPLY in
q|Q) echo "Program terminated."
exit
;;
a|A) echo "Hostname: $HOSTNAME"
uptime
;;
b|B) df -h
;;
c|C) if [[ $(id -u) -eq 0 ]]; then
echo "Home Space Utilization (All Users)"
du -sh /home/*
else
echo "Home Space Utilization ($USER)"
du -sh $HOME
fi
;;
*) echo "Invalid entry" >&2
exit 1
;;
esac
```

fall through case pattern (`;;&`)

```bash
#!/bin/bash
# case4-2: test a character
read -n 1 -p "Type a character > "
echo
case $REPLY in
[[:upper:]]) echo "'$REPLY' is upper case." ;;&
[[:lower:]]) echo "'$REPLY' is lower case." ;;&
[[:alpha:]]) echo "'$REPLY' is alphabetic." ;;&
[[:digit:]]) echo "'$REPLY' is a digit." ;;&
[[:graph:]]) echo "'$REPLY' is a visible character." ;;&
[[:punct:]]) echo "'$REPLY' is a punctuation symbol." ;;&
[[:space:]]) echo "'$REPLY' is a whitespace character." ;;&
[[:xdigit:]]) echo "'$REPLY' is a hexadecimal digit." ;;&
esac
```
#### for语句
```bash
Expand All @@ -1101,10 +1290,9 @@ for 变量 in 值1 值2 值3 …… 值n
{1..50} # 1 2 ... 50
{0..10..2} # 0 2 4 6 8 10

for (( 初始值;循环控制条件;变量变化 ))
do
程序
done
for (( 初始值;循环控制条件;变量变化 )); do
程序
done
```
#### while语句与until语句
Expand All @@ -1121,6 +1309,14 @@ until [[ 条件判断式 ]]
done
```
```bash
(( expression1 ))
while (( expression2 )); do
commands
(( expression3 ))
done
```
```bash
#!/bin/bash
# while-menu: a menu driven system information program
Expand Down Expand Up @@ -1174,7 +1370,11 @@ while read distro version release; do
done < distros.txt
```
### 函数
### Bash Array
- [Array Reference](http://billie66.github.io/TLCL/book/chap36.html)
### Bash Function
- 函数局部变量 local + 变量名
- 函数参数 : $ + #/？/@/n
Expand Down Expand Up @@ -1263,6 +1463,31 @@ else
fi
```
```bash
# interactive mode
if [[ -n $interactive ]]; then
while true; do
read -p "Enter name of output file: " filename
if [[ -e $filename ]]; then
read -p "'$filename' exists. Overwrite? [y/n/q] > "
case $REPLY in
Y|y) break
;;
Q|q) echo "Program terminated."
exit
;;
*) continue
;;
esac
elif [[ -z $filename ]]; then
continue
else
break
fi
done
fi
```
### 信号
- man 7 signal —— 传递信号给进程
Expand Down

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