119 lines
1.9 KiB
Markdown
119 lines
1.9 KiB
Markdown
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---
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title: "Some basic bash-script code block"
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time: "2022-11-29"
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tags: ["linux"]
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summary: "Some basic bash-script code example. It might be help if writing some temporary work-scripts."
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---
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### Assignment and Substitution
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```bash
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a=375
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hello=$a
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```
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### Variables
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1. Built-in Variables
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For example `$HOME $PWD ...`, for more info, see [environ(7)](https://man7.org/linux/man-pages/man7/environ.7.html)
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2. Positional Parameters
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**echo** $para1 $para2 $para3 $para4 $0 $1 $2 $3 $4 $@
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3. Special Parameters
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$? # exit status of a command, function, or the script itself
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### Branches
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```bash
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if [ condition1 ];then
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command_series1
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elif [ condition2 ];then
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command_series2
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else
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default_command_series3
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fi
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```
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### Loops
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### range for
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```bash
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for arg in `seq 10`; do
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echo $arg
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done
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```
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### for in C-like syntax
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```bash
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LIMIT=10
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for ((a=1; a<=LIMIT; a++)); do
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echo "$a "
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done
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```
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### **while**
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```bash
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LIMIT=10
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a=1
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while ((a<=LIMIT)); do
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echo "$a "
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((a += 1))
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done
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```
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### IO
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```bash
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command < input-file > output-file # rewrite
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command >> output-file # appending
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```
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### Function
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```bash
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# define a function
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function fun_name(){
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command...
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}
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## or
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fun_name(){ # arg1 arg2 arg3
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command...
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}
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# apply a function
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fun_name $arg1 $arg2 $arg3
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# dereference
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fun_name(){ # arg1
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eval "$1=hello"
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}
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fun_name arg1
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## the above code block is equivalent to
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arg1=hello
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```
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### Debugging
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1. take good use of sh(1)
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for example:
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sh -n script: checks for syntax
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sh -v script: echo each command before executing it
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sh -x script: echo the result of each command in an abbreviated manner
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2. use echo
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3. use trap
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### Parallel
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use GNU parallel
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### Script with Style
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1. Comment your code
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2. Avoid using magic number
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3. Use exit codes in a systematic and meaningful way
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4. Use standardized parameter flags for script invocation
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