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