posix-shell-pro

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Original

English

🇨🇳

Translation

Chinese

Use this skill when

何时使用此技能

Working on posix shell pro tasks or workflows
Needing guidance, best practices, or checklists for posix shell pro

处理POSIX Shell专业任务或工作流时
需要POSIX Shell领域的指导、最佳实践或检查清单时

Do not use this skill when

何时不使用此技能

The task is unrelated to posix shell pro
You need a different domain or tool outside this scope

任务与POSIX Shell无关时
需要此范围之外的其他领域或工具时

Instructions

说明

Clarify goals, constraints, and required inputs.
Apply relevant best practices and validate outcomes.
Provide actionable steps and verification.
If detailed examples are required, open
```
resources/implementation-playbook.md
```
.

明确目标、约束条件和所需输入。
应用相关最佳实践并验证结果。
提供可执行步骤和验证方法。
如果需要详细示例，请打开
```
resources/implementation-playbook.md
```
。

Focus Areas

重点领域

Strict POSIX compliance for maximum portability
Shell-agnostic scripting that works on any Unix-like system
Defensive programming with portable error handling
Safe argument parsing without bash-specific features
Portable file operations and resource management
Cross-platform compatibility (Linux, BSD, Solaris, AIX, macOS)
Testing with dash, ash, and POSIX mode validation
Static analysis with ShellCheck in POSIX mode
Minimalist approach using only POSIX-specified features
Compatibility with legacy systems and embedded environments

严格遵循POSIX标准以实现最大可移植性
与Shell无关的脚本编写，可在任何类Unix系统上运行
具备可移植错误处理的防御式编程
不依赖bash特定特性的安全参数解析
可移植的文件操作和资源管理
跨平台兼容性（Linux、BSD、Solaris、AIX、macOS）
使用dash、ash和POSIX模式验证进行测试
在POSIX模式下使用ShellCheck进行静态分析
仅使用POSIX指定特性的极简主义方法
与遗留系统和嵌入式环境的兼容性

POSIX Constraints

POSIX约束条件

No arrays (use positional parameters or delimited strings)
No
```
[[
```
conditionals (use
```
[
```
test command only)
No process substitution
```
<()
```
or
```
>()
```
No brace expansion
```
{1..10}
```
No
```
local
```
keyword (use function-scoped variables carefully)
No
```
declare
```
,
```
typeset
```
, or
```
readonly
```
for variable attributes
No
```
+=
```
operator for string concatenation
No
```
${var//pattern/replacement}
```
substitution
No associative arrays or hash tables
No
```
source
```
command (use
```
.
```
for sourcing files)

不使用数组（使用位置参数或分隔字符串）
不使用
```
[[
```
条件判断（仅使用
```
[
```
测试命令）
不使用进程替换
```
<()
```
或
```
>()
```
不使用大括号扩展
```
{1..10}
```
不使用
```
local
```
关键字（谨慎使用函数作用域变量）
不使用
```
declare
```
、
```
typeset
```
或
```
readonly
```
设置变量属性
不使用
```
+=
```
运算符进行字符串拼接
不使用
```
${var//pattern/replacement}
```
替换
不使用关联数组或哈希表
不使用
```
source
```
命令（使用
```
.
```
来加载文件）

Approach

方法

Always use
```
#!/bin/sh
```
shebang for POSIX shell
Use
```
set -eu
```
for error handling (no
```
pipefail
```
in POSIX)
Quote all variable expansions:
```
"$var"
```
never
```
$var
```
Use
```
[ ]
```
for all conditional tests, never
```
[[
```
Implement argument parsing with
```
while
```
and
```
case
```
(no
```
getopts
```
for long options)
Create temporary files safely with
```
mktemp
```
and cleanup traps
Use
```
printf
```
instead of
```
echo
```
for all output (echo behavior varies)
Use
```
. script.sh
```
instead of
```
source script.sh
```
for sourcing
Implement error handling with explicit
```
|| exit 1
```
checks
Design scripts to be idempotent and support dry-run modes
Use
```
IFS
```
manipulation carefully and restore original value
Validate inputs with
```
[ -n "$var" ]
```
and
```
[ -z "$var" ]
```
tests
End option parsing with
```
--
```
and use
```
rm -rf -- "$dir"
```
for safety
Use command substitution
```
$()
```
instead of backticks for readability
Implement structured logging with timestamps using
```
date
```
Test scripts with dash/ash to verify POSIX compliance

始终使用
```
#!/bin/sh
```
作为POSIX Shell的shebang
使用
```
set -eu
```
进行错误处理（POSIX不支持
```
pipefail
```
）
对所有变量扩展添加引号：始终使用
```
"$var"
```
而非
```
$var
```
所有条件测试使用
```
[ ]
```
，绝不使用
```
[[
```
使用
```
while
```
和
```
case
```
实现参数解析（长选项不使用
```
getopts
```
）
使用
```
mktemp
```
安全创建临时文件，并通过清理陷阱进行清理
所有输出使用
```
printf
```
而非
```
echo
```
（echo的行为因实现而异）
使用
```
. script.sh
```
而非
```
source script.sh
```
来加载脚本
使用显式的
```
|| exit 1
```
检查实现错误处理
将脚本设计为幂等性并支持空运行模式
谨慎操作
```
IFS
```
并恢复其原始值
使用
```
[ -n "$var" ]
```
和
```
[ -z "$var" ]
```
测试验证输入
使用
```
--
```
结束选项解析，并使用
```
rm -rf -- "$dir"
```
确保安全
使用命令替换
```
$()
```
而非反引号以提高可读性
使用
```
date
```
实现带时间戳的结构化日志
使用dash/ash测试脚本以验证POSIX兼容性

Compatibility & Portability

兼容性与可移植性

Use
```
#!/bin/sh
```
to invoke the system's POSIX shell
Test on multiple shells: dash (Debian/Ubuntu default), ash (Alpine/BusyBox), bash --posix
Avoid GNU-specific options; use POSIX-specified flags only
Handle platform differences:
```
uname -s
```
for OS detection
Use
```
command -v
```
instead of
```
which
```
(more portable)

Check for command availability:

command -v cmd >/dev/null 2>&1 || exit 1

Provide portable implementations for missing utilities
Use
```
[ -e "$file" ]
```
for existence checks (works on all systems)
Avoid
```
/dev/stdin
```
,
```
/dev/stdout
```
(not universally available)
Use explicit redirection instead of
```
&>
```
(bash-specific)

使用
```
#!/bin/sh
```
调用系统的POSIX Shell
在多个Shell上测试：dash（Debian/Ubuntu默认）、ash（Alpine/BusyBox）、bash --posix
避免GNU特定选项；仅使用POSIX指定的标志
处理平台差异：使用
```
uname -s
```
检测操作系统
使用
```
command -v
```
而非
```
which
```
（更具可移植性）

检查命令可用性：

command -v cmd >/dev/null 2>&1 || exit 1

为缺失的工具提供可移植的实现方案
使用
```
[ -e "$file" ]
```
进行存在性检查（适用于所有系统）
避免使用
```
/dev/stdin
```
、
```
/dev/stdout
```
（并非所有系统都支持）
使用显式重定向而非
```
&>
```
（bash特定特性）

Readability & Maintainability

可读性与可维护性

Use descriptive variable names in UPPER_CASE for exports, lower_case for locals
Add section headers with comment blocks for organization
Keep functions under 50 lines; extract complex logic
Use consistent indentation (spaces only, typically 2 or 4)
Document function purpose and parameters in comments
Use meaningful names:
```
validate_input
```
not
```
check
```
Add comments for non-obvious POSIX workarounds
Group related functions with descriptive headers
Extract repeated code into functions
Use blank lines to separate logical sections

导出变量使用大写描述性名称，局部变量使用小写
添加带注释块的节标题以组织代码
函数代码不超过50行；提取复杂逻辑
使用一致的缩进（仅使用空格，通常为2或4个）
在注释中记录函数的用途和参数
使用有意义的名称：如
```
validate_input
```
而非
```
check
```
为非显而易见的POSIX解决方案添加注释
将相关函数分组并添加描述性标题
将重复代码提取为函数
使用空行分隔逻辑部分

Safety & Security Patterns

安全与安全模式

Quote all variable expansions to prevent word splitting
Validate file permissions before operations:
```
[ -r "$file" ] || exit 1
```
Sanitize user input before using in commands
Validate numeric input:
```
case $num in *[!0-9]*) exit 1 ;; esac
```
Never use
```
eval
```
on untrusted input
Use
```
--
```
to separate options from arguments:
```
rm -- "$file"
```

Validate required variables:

[ -n "$VAR" ] || { echo "VAR required" >&2; exit 1; }

Check exit codes explicitly:
```
cmd || { echo "failed" >&2; exit 1; }
```

Use

trap

for cleanup:

trap 'rm -f "$tmpfile"' EXIT INT TERM

Set restrictive umask for sensitive files:
```
umask 077
```
Log security-relevant operations to syslog or file
Validate file paths don't contain unexpected characters
Use full paths for commands in security-critical scripts:
```
/bin/rm
```
not
```
rm
```

对所有变量扩展添加引号以防止单词拆分
操作前验证文件权限：
```
[ -r "$file" ] || exit 1
```
在命令中使用前清理用户输入
验证数值输入：
```
case $num in *[!0-9]*) exit 1 ;; esac
```
绝不使用
```
eval
```
处理不可信输入
使用
```
--
```
分隔选项和参数：
```
rm -- "$file"
```

验证必填变量：

[ -n "$VAR" ] || { echo "VAR required" >&2; exit 1; }

显式检查退出码：
```
cmd || { echo "failed" >&2; exit 1; }
```

使用

trap

进行清理：

trap 'rm -f "$tmpfile"' EXIT INT TERM

为敏感文件设置严格的umask：
```
umask 077
```
将安全相关操作记录到syslog或文件中
验证文件路径不包含意外字符
在安全关键脚本中使用命令的完整路径：如
```
/bin/rm
```
而非
```
rm
```

Performance Optimization

性能优化

Use shell built-ins over external commands when possible
Avoid spawning subshells in loops: use
```
while read
```
not
```
for i in $(cat)
```
Cache command results in variables instead of repeated execution
Use
```
case
```
for multiple string comparisons (faster than repeated
```
if
```
)
Process files line-by-line for large files
Use
```
expr
```
or
```
$(( ))
```
for arithmetic (POSIX supports
```
$(( ))
```
)
Minimize external command calls in tight loops
Use
```
grep -q
```
when you only need true/false (faster than capturing output)
Batch similar operations together
Use here-documents for multi-line strings instead of multiple echo calls

尽可能使用Shell内置命令而非外部命令
避免在循环中生成子shell：使用
```
while read
```
而非
```
for i in $(cat)
```
将命令结果缓存到变量中而非重复执行
使用
```
case
```
进行多字符串比较（比重复
```
if
```
更快）
对大文件逐行处理
使用
```
expr
```
或
```
$(( ))
```
进行算术运算（POSIX支持
```
$(( ))
```
）
在紧凑循环中尽量减少外部命令调用
仅需要真假结果时使用
```
grep -q
```
（比捕获输出更快）
将相似操作批量处理
使用here-document处理多行字符串而非多次调用echo

Documentation Standards

文档标准

Implement
```
-h
```
flag for help (avoid
```
--help
```
without proper parsing)
Include usage message showing synopsis and options
Document required vs optional arguments clearly
List exit codes: 0=success, 1=error, specific codes for specific failures
Document prerequisites and required commands
Add header comment with script purpose and author
Include examples of common usage patterns
Document environment variables used by script
Provide troubleshooting guidance for common issues
Note POSIX compliance in documentation

实现
```
-h
```
标志以提供帮助（无适当解析时避免使用
```
--help
```
）
包含显示概要和选项的使用信息
明确记录必填与可选参数
列出退出码：0=成功，1=错误，特定错误对应特定代码
记录先决条件和所需命令
添加包含脚本用途和作者的头部注释
包含常见使用模式的示例
记录脚本使用的环境变量
提供常见问题的故障排除指南
在文档中注明POSIX兼容性

Working Without Arrays

不使用数组的处理方式

Since POSIX sh lacks arrays, use these patterns:

Positional Parameters:

set -- item1 item2 item3; for arg; do echo "$arg"; done

Delimited Strings:

items="a:b:c"; IFS=:; set -- $items; IFS=' '

Newline-Separated:

items="a\nb\nc"; while IFS= read -r item; do echo "$item"; done <<EOF

Counters:

i=0; while [ $i -lt 10 ]; do i=$((i+1)); done

Field Splitting: Use
```
cut
```
,
```
awk
```
, or parameter expansion for string splitting

由于POSIX sh不支持数组，可使用以下模式：

位置参数：

set -- item1 item2 item3; for arg; do echo "$arg"; done

分隔字符串：

items="a:b:c"; IFS=:; set -- $items; IFS=' '

换行分隔：

items="a\nb\nc"; while IFS= read -r item; do echo "$item"; done <<EOF

计数器：

i=0; while [ $i -lt 10 ]; do i=$((i+1)); done

字段拆分：使用
```
cut
```
、
```
awk
```
或参数扩展进行字符串拆分

Portable Conditionals

可移植条件判断

Use

[ ]

test command with POSIX operators:

File Tests:
```
[ -e file ]
```
exists,
```
[ -f file ]
```
regular file,
```
[ -d dir ]
```
directory

String Tests:

[ -z "$str" ]

empty,

[ -n "$str" ]

not empty,

[ "$a" = "$b" ]

equal

Numeric Tests:
```
[ "$a" -eq "$b" ]
```
equal,
```
[ "$a" -lt "$b" ]
```
less than

Logical:

[ cond1 ] && [ cond2 ]

AND,

[ cond1 ] || [ cond2 ]

Negation:
```
[ ! -f file ]
```
not a file
Pattern Matching: Use
```
case
```
not
```
[[ =~ ]]
```

使用带POSIX运算符的

[ ]

测试命令：

文件测试：
```
[ -e file ]
```
存在，
```
[ -f file ]
```
普通文件，
```
[ -d dir ]
```
目录
字符串测试：
```
[ -z "$str" ]
```
为空，
```
[ -n "$str" ]
```
非空，
```
[ "$a" = "$b" ]
```
相等
数值测试：
```
[ "$a" -eq "$b" ]
```
相等，
```
[ "$a" -lt "$b" ]
```
小于

逻辑运算：

[ cond1 ] && [ cond2 ]

逻辑与，

[ cond1 ] || [ cond2 ]

逻辑或

取反：
```
[ ! -f file ]
```
不是文件
模式匹配：使用
```
case
```
而非
```
[[ =~ ]]
```

CI/CD Integration

CI/CD集成

Matrix testing: Test across dash, ash, bash --posix, yash on Linux, macOS, Alpine
Container testing: Use alpine:latest (ash), debian:stable (dash) for reproducible tests
Pre-commit hooks: Configure checkbashisms, shellcheck -s sh, shfmt -ln posix
GitHub Actions: Use shellcheck-problem-matchers with POSIX mode
Cross-platform validation: Test on Linux, macOS, FreeBSD, NetBSD
BusyBox testing: Validate on BusyBox environments for embedded systems
Automated releases: Tag versions and generate portable distribution packages
Coverage tracking: Ensure test coverage across all POSIX shells

Example workflow:

shellcheck -s sh *.sh && shfmt -ln posix -d *.sh && checkbashisms *.sh

矩阵测试：在Linux、macOS、Alpine上的dash、ash、bash --posix、yash中测试
容器测试：使用alpine:latest（ash）、debian:stable（dash）进行可重现测试
预提交钩子：配置checkbashisms、shellcheck -s sh、shfmt -ln posix
GitHub Actions：使用ShellCheck问题匹配器的POSIX模式
跨平台验证：在Linux、macOS、FreeBSD、NetBSD上测试
BusyBox测试：在嵌入式系统的BusyBox环境中验证
自动化发布：标记版本并生成可移植的发行包
覆盖率跟踪：确保所有POSIX Shell的测试覆盖率

示例工作流：

shellcheck -s sh *.sh && shfmt -ln posix -d *.sh && checkbashisms *.sh

Embedded Systems & Limited Environments

嵌入式系统与受限环境

BusyBox compatibility: Test with BusyBox's limited ash implementation
Alpine Linux: Default shell is BusyBox ash, not bash
Resource constraints: Minimize memory usage, avoid spawning excessive processes
Missing utilities: Provide fallbacks when common tools unavailable (
```
mktemp
```
,
```
seq
```
)
Read-only filesystems: Handle scenarios where
```
/tmp
```
may be restricted
No coreutils: Some environments lack GNU coreutils extensions
Signal handling: Limited signal support in minimal environments
Startup scripts: Init scripts must be POSIX for maximum compatibility

Example: Check for mktemp:

command -v mktemp >/dev/null 2>&1 || mktemp() { ... }

BusyBox兼容性：使用BusyBox受限的ash实现进行测试
Alpine Linux：默认Shell是BusyBox ash而非bash
资源约束：最小化内存使用，避免生成过多进程
缺失工具：当常用工具不可用时提供回退方案（
```
mktemp
```
、
```
seq
```
）
只读文件系统：处理
```
/tmp
```
可能受限制的场景
无coreutils：某些环境缺少GNU coreutils扩展
信号处理：受限环境中的信号支持有限
启动脚本：初始化脚本必须遵循POSIX标准以实现最大兼容性

示例：检查mktemp是否存在：

command -v mktemp >/dev/null 2>&1 || mktemp() { ... }

Migration from Bash to POSIX sh

从Bash迁移到POSIX sh

Assessment: Run
```
checkbashisms
```
to identify bash-specific constructs
Array elimination: Convert arrays to delimited strings or positional parameters
Conditional updates: Replace
```
[[
```
with
```
[
```
and adjust regex to
```
case
```
patterns
Local variables: Remove
```
local
```
keyword, use function prefixes instead
Process substitution: Replace
```
<()
```
with temporary files or pipes
Parameter expansion: Use
```
sed
```
/
```
awk
```
for complex string manipulation
Testing strategy: Incremental conversion with continuous validation
Documentation: Note any POSIX limitations or workarounds
Gradual migration: Convert one function at a time, test thoroughly
Fallback support: Maintain dual implementations during transition if needed

评估：运行
```
checkbashisms
```
识别bash特定结构
移除数组：将数组转换为分隔字符串或位置参数
更新条件判断：将
```
[[
```
替换为
```
[
```
，并将正则表达式调整为
```
case
```
模式
局部变量：移除
```
local
```
关键字，改用函数前缀
进程替换：将
```
<()
```
替换为临时文件或管道
参数扩展：使用
```
sed
```
/
```
awk
```
进行复杂字符串操作
测试策略：逐步转换并持续验证
文档：记录任何POSIX限制或解决方案
逐步迁移：一次转换一个函数，彻底测试
回退支持：过渡期间如需维护双重实现

Quality Checklist

质量检查清单

Scripts pass ShellCheck with
```
-s sh
```
flag (POSIX mode)
Code is formatted consistently with shfmt using
```
-ln posix
```
Test on multiple shells: dash, ash, bash --posix, yash
All variable expansions are properly quoted
No bash-specific features used (arrays,
```
[[
```
,
```
local
```
, etc.)
Error handling covers all failure modes
Temporary resources cleaned up with EXIT trap
Scripts provide clear usage information
Input validation prevents injection attacks
Scripts portable across Unix-like systems (Linux, BSD, Solaris, macOS, Alpine)
BusyBox compatibility validated for embedded use cases
No GNU-specific extensions or flags used

脚本通过
```
-s sh
```
标志的ShellCheck检查（POSIX模式）
代码使用shfmt的
```
-ln posix
```
选项进行一致格式化
在多个Shell上测试：dash、ash、bash --posix、yash
所有变量扩展都正确添加了引号
未使用bash特定特性（数组、
```
[[
```
、
```
local
```
等）
错误处理覆盖所有失败模式
临时资源通过EXIT陷阱清理
脚本提供清晰的使用信息
输入验证防止注入攻击
脚本可在类Unix系统（Linux、BSD、Solaris、macOS、Alpine）间移植
针对嵌入式用例验证了BusyBox兼容性
未使用GNU特定扩展或标志

Output

输出成果

POSIX-compliant shell scripts maximizing portability
Test suites using shellspec or bats-core validating across dash, ash, yash
CI/CD configurations for multi-shell matrix testing
Portable implementations of common patterns with fallbacks
Documentation on POSIX limitations and workarounds with examples
Migration guides for converting bash scripts to POSIX sh incrementally
Cross-platform compatibility matrices (Linux, BSD, macOS, Solaris, Alpine)
Performance benchmarks comparing different POSIX shells
Fallback implementations for missing utilities (mktemp, seq, timeout)
BusyBox-compatible scripts for embedded and container environments
Package distributions for various platforms without bash dependency

遵循POSIX标准的Shell脚本，实现最大可移植性
使用shellspec或bats-core的测试套件，在dash、ash、yash中验证
用于多Shell矩阵测试的CI/CD配置
带回退方案的通用模式可移植实现
含示例的POSIX限制与解决方案文档
逐步将Bash脚本转换为POSIX sh的迁移指南
跨平台兼容性矩阵（Linux、BSD、macOS、Solaris、Alpine）
不同POSIX Shell的性能基准测试
缺失工具的回退实现（mktemp、seq、timeout）
适用于嵌入式和容器环境的BusyBox兼容脚本
不依赖bash的多平台发行包

Essential Tools

必备工具

Static Analysis & Formatting

静态分析与格式化

ShellCheck: Static analyzer with
```
-s sh
```
for POSIX mode validation
shfmt: Shell formatter with
```
-ln posix
```
option for POSIX syntax
checkbashisms: Detects bash-specific constructs in scripts (from devscripts)
Semgrep: SAST with POSIX-specific security rules
CodeQL: Security scanning for shell scripts

ShellCheck：静态分析器，使用
```
-s sh
```
进行POSIX模式验证
shfmt：Shell格式化工具，支持
```
-ln posix
```
选项的POSIX语法
checkbashisms：检测脚本中的bash特定结构（来自devscripts）
Semgrep：SAST工具，含POSIX特定安全规则
CodeQL：Shell脚本安全扫描工具

POSIX Shell Implementations for Testing

用于测试的POSIX Shell实现

dash: Debian Almquist Shell - lightweight, strict POSIX compliance (primary test target)
ash: Almquist Shell - BusyBox default, embedded systems
yash: Yet Another Shell - strict POSIX conformance validation
posh: Policy-compliant Ordinary Shell - Debian policy compliance
osh: Oil Shell - modern POSIX-compatible shell with better error messages
bash --posix: GNU Bash in POSIX mode for compatibility testing

dash：Debian Almquist Shell - 轻量级，严格遵循POSIX标准（主要测试目标）
ash：Almquist Shell - BusyBox默认Shell，适用于嵌入式系统
yash：Yet Another Shell - 严格的POSIX合规性验证
posh：Policy-compliant Ordinary Shell - 符合Debian策略
osh：Oil Shell - 现代POSIX兼容Shell，提供更友好的错误信息
bash --posix：GNU Bash的POSIX模式，用于兼容性测试

Testing Frameworks

测试框架

bats-core: Bash testing framework (works with POSIX sh)
shellspec: BDD-style testing that supports POSIX sh
shunit2: xUnit-style framework with POSIX sh support
sharness: Test framework used by Git (POSIX-compatible)

bats-core：Bash测试框架（可用于POSIX sh）
shellspec：支持POSIX sh的BDD风格测试框架
shunit2：支持POSIX sh的xUnit风格框架
sharness：Git使用的测试框架（兼容POSIX）

Common Pitfalls to Avoid

常见陷阱与规避方法

Using
```
[[
```
instead of
```
[
```
(bash-specific)
Using arrays (not in POSIX sh)
Using
```
local
```
keyword (bash/ksh extension)
Using
```
echo
```
without
```
printf
```
(behavior varies across implementations)
Using
```
source
```
instead of
```
.
```
for sourcing scripts
Using bash-specific parameter expansion:
```
${var//pattern/replacement}
```
Using process substitution
```
<()
```
or
```
>()
```
Using
```
function
```
keyword (ksh/bash syntax)
Using
```
$RANDOM
```
variable (not in POSIX)
Using
```
read -a
```
for arrays (bash-specific)
Using
```
set -o pipefail
```
(bash-specific)
Using
```
&>
```
for redirection (use
```
>file 2>&1
```
)

使用
```
[[
```
而非
```
[
```
（bash特定）
使用数组（POSIX sh不支持）
使用
```
local
```
关键字（bash/ksh扩展）
使用
```
echo
```
而非
```
printf
```
（不同实现行为不同）
使用
```
source
```
而非
```
.
```
加载脚本
使用bash特定参数扩展：
```
${var//pattern/replacement}
```
使用进程替换
```
<()
```
或
```
>()
```
使用
```
function
```
关键字（ksh/bash语法）
使用
```
$RANDOM
```
变量（POSIX不支持）
使用
```
read -a
```
处理数组（bash特定）
使用
```
set -o pipefail
```
（bash特定）
使用
```
&>
```
进行重定向（应使用
```
>file 2>&1
```
）

Advanced Techniques

高级技巧

Error Trapping:

trap 'echo "Error at line $LINENO" >&2; exit 1' EXIT; trap - EXIT

on success

Safe Temp Files:

tmpfile=$(mktemp) || exit 1; trap 'rm -f "$tmpfile"' EXIT INT TERM

Simulating Arrays:

set -- item1 item2 item3; for arg; do process "$arg"; done

Field Parsing:

IFS=:; while read -r user pass uid gid; do ...; done < /etc/passwd

String Replacement:
```
echo "$str" | sed 's/old/new/g'
```
or use parameter expansion
```
${str%suffix}
```
Default Values:
```
value=${var:-default}
```
assigns default if var unset or null
Portable Functions: Avoid
```
function
```
keyword, use
```
func_name() { ... }
```
Subshell Isolation:
```
(cd dir && cmd)
```
changes directory without affecting parent
Here-documents:
```
cat <<'EOF'
```
with quotes prevents variable expansion

Command Existence:

command -v cmd >/dev/null 2>&1 && echo "found" || echo "missing"

错误捕获：

trap 'echo "Error at line $LINENO" >&2; exit 1' EXIT; trap - EXIT

（成功时移除陷阱）

安全临时文件：

tmpfile=$(mktemp) || exit 1; trap 'rm -f "$tmpfile"' EXIT INT TERM

模拟数组：

set -- item1 item2 item3; for arg; do process "$arg"; done

字段解析：

IFS=:; while read -r user pass uid gid; do ...; done < /etc/passwd

字符串替换：

echo "$str" | sed 's/old/new/g'

或使用参数扩展

${str%suffix}

默认值：
```
value=${var:-default}
```
（当var未设置或为空时分配默认值）
可移植函数：避免使用
```
function
```
关键字，使用
```
func_name() { ... }
```
子shell隔离：
```
(cd dir && cmd)
```
（更改目录而不影响父shell）
Here-document：
```
cat <<'EOF'
```
（带引号可防止变量扩展）

命令存在性检查：

command -v cmd >/dev/null 2>&1 && echo "found" || echo "missing"

POSIX-Specific Best Practices

POSIX特定最佳实践

Always quote variable expansions:
```
"$var"
```
not
```
$var
```
Use
```
[ ]
```
with proper spacing:
```
[ "$a" = "$b" ]
```
not
```
["$a"="$b"]
```
Use
```
=
```
for string comparison, not
```
==
```
(bash extension)
Use
```
.
```
for sourcing, not
```
source
```
Use
```
printf
```
for all output, avoid
```
echo -e
```
or
```
echo -n
```
Use
```
$(( ))
```
for arithmetic, not
```
let
```
or
```
declare -i
```
Use
```
case
```
for pattern matching, not
```
[[ =~ ]]
```
Test scripts with
```
sh -n script.sh
```
to check syntax
Use
```
command -v
```
not
```
type
```
or
```
which
```
for portability
Explicitly handle all error conditions with
```
|| exit 1
```

始终对变量扩展添加引号：使用
```
"$var"
```
而非
```
$var
```
使用
```
[ ]
```
时保持适当空格：
```
[ "$a" = "$b" ]
```
而非
```
["$a"="$b"]
```
字符串比较使用
```
=
```
而非
```
==
```
（bash扩展）
加载文件使用
```
.
```
而非
```
source
```
所有输出使用
```
printf
```
，避免
```
echo -e
```
或
```
echo -n
```
算术运算使用
```
$(( ))
```
而非
```
let
```
或
```
declare -i
```
模式匹配使用
```
case
```
而非
```
[[ =~ ]]
```
使用
```
sh -n script.sh
```
检查脚本语法
可移植性检查使用
```
command -v
```
而非
```
type
```
或
```
which
```
使用
```
|| exit 1
```
显式处理所有错误情况

References & Further Reading

参考资料与进一步阅读

POSIX Standards & Specifications

POSIX标准与规范

POSIX Shell Command Language - Official POSIX.1-2024 specification
POSIX Utilities - Complete list of POSIX-mandated utilities
Autoconf Portable Shell Programming - Comprehensive portability guide from GNU

POSIX Shell Command Language - 官方POSIX.1-2024规范
POSIX Utilities - POSIX规定的完整工具列表
Autoconf Portable Shell Programming - GNU提供的全面可移植性指南

Portability & Best Practices

可移植性与最佳实践

Rich's sh (POSIX shell) tricks - Advanced POSIX shell techniques
Suckless Shell Style Guide - Minimalist POSIX sh patterns
FreeBSD Porter's Handbook - Shell - BSD portability considerations

Rich's sh (POSIX shell) tricks - 高级POSIX Shell技巧
Suckless Shell Style Guide - 极简主义POSIX sh模式
FreeBSD Porter's Handbook - Shell - BSD可移植性注意事项

Tools & Testing

工具与测试

checkbashisms - Detect bash-specific constructs

checkbashisms - 检测脚本中的bash特定结构