Go 命令行工具:管道数据
unix 因倡导命令应该做一件事并做好它的理念而闻名。
复杂的数据处理和转换操作通常可以使用 shell 管道运算符将命令链接在一起来执行,以便一个命令的输出成为另一个命令的输入,操作和转换数据以实现所需的结果。
例如:
# sort file names. | |
ls | sort | |
# count files. | |
ls -l | count -l | |
# print out unique file extensions. | |
# 1. list all files that have extensions | |
# 2. transform the data (discard everything but extensions) | |
# 3. sort the list (data must be sorted to identify duplicates) | |
# 4. filter out duplicates | |
# 5. browse the results | |
ls *.* | sed 's/.*\.//' | sort | uniq | less |
使用 go,程序员可以创建高效且高性能的命令来处理数据。我们将通过以下片段来讨论这个问题。
添加行号到输出
可用于管道操作的命令的本质是从 stdin 读取并写入 stdout。
add-line-numbers.go
package main | |
import ( | |
"bufio" | |
"fmt" | |
"os" | |
) | |
func main() { | |
// buffered input that splits input on lines. | |
input := bufio.newscanner(os.stdin) | |
// buffered output. | |
output := bufio.newwriter(os.stdout) | |
lineno := 0 | |
// scan until eof (no more input). | |
for input.scan() { | |
text := input.text() | |
lineno++ | |
s := fmt.sprintf("%03d %s\n", lineno, text) | |
// it would be simpler to just use fmt.println, | |
// but want to emphasize piping stdin to stdout | |
// explicitly. | |
// intentionally ignoring return values. | |
_, _ = output.writestring(s) | |
} | |
// always explicitly flush remaining buffered output. | |
_ = output.flush() | |
} |
此示例从 stdin 一次读取一行,并将其写回到 stdout,每行都以行号为前缀。在这里,我们使用程序文件本身作为输入来生成编号的输出。
$ cat add-line-numbers.go | go run add-line-numbers.go | |
001 package main | |
002 | |
003 import ( | |
004 "bufio" | |
005 "fmt" | |
006 "os" | |
007 ) | |
008 | |
009 func main() { | |
010 | |
011 // buffered input that splits input on lines. | |
012 input := bufio.newscanner(os.stdin) | |
013 | |
014 // buffered output. | |
015 output := bufio.newwriter(os.stdout) | |
016 | |
017 lineno := 0 | |
018 | |
019 // scan until eof (no more input). | |
020 for input.scan() { | |
021 text := input.text() | |
022 lineno++ | |
023 s := fmt.sprintf("%03d %s\n", lineno, text) | |
024 | |
025 // it would be simpler to just use fmt.println, | |
026 // but want to emphasize piping stdin to stdout | |
027 // explicitly. | |
028 // intentionally ignoring return values. | |
029 _, _ = output.writestring(s) | |
030 | |
031 } | |
032 | |
033 // always explicitly flush remaining buffered output. | |
034 _ = output.flush() | |
035 | |
036 } |
base64编码输入
此示例从 stdin 一次读取一行,base64 对其进行编码,然后将其写回到 stdout。
package main | |
import ( | |
"bufio" | |
"encoding/base64" | |
"os" | |
) | |
func main() { | |
// buffered input that splits input on lines. | |
input := bufio.newscanner(os.stdin) | |
// base64 encoder/writer. | |
encoder := base64.newencoder( | |
base64.stdencoding, | |
os.stdout) | |
// scan until eof (no more input). | |
for input.scan() { | |
bytes := input.bytes() | |
_, _ = encoder.write(bytes) | |
_, _ = encoder.write([]byte{'\n'}) | |
} | |
// close the encoder and ensure it flushes remaining output | |
_ = encoder.close() | |
} |
由于扫描器会分割换行符 (n) 而不返回它们,因此有必要在写入每一行后显式写入换行符。
$ cat base64-encode.go | go run base64-encode.go | |
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 |
您可以通过将编码结果传输到系统 base64 命令(linux 和 macos)进行解码来确认文本是否正确编码:
$ cat base64-encode.go | go run base64-encode.go | base64 -D | |
package main | |
import ( | |
"bufio" | |
"encoding/base64" | |
"os" | |
) | |
func main() { | |
// Buffered input that splits input on lines. | |
input := bufio.NewScanner(os.Stdin) | |
// Base64 Encoder/writer. | |
encoder := base64.NewEncoder( | |
base64.StdEncoding, | |
os.Stdout) | |
// Scan until EOF (no more input). | |
for input.Scan() { | |
bytes := input.Bytes() | |
_, _ = encoder.Write(bytes) | |
_, _ = encoder.Write([]byte{'\n'}) | |
} | |
// Close the encoder and ensure it flushes remaining output | |
_ = encoder.Close() | |
} |
这篇文章摘录自我编写的关于 go 标准库功能的简短介绍性指南,这些功能对于创建命令行工具非常有用:go for cli 应用程序和工具。
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