Shell printf 命令

基本格式

Bash

printf "hello %s\n" "world"
printf "%d + %d = %d\n" 2 3 5
printf "%.2f\n" 3.14159
printf "%x %X\n" 255 255

Output

hello world
2 + 3 = 5
3.14
ff FF

Bash

printf "%-10s|%10s|\n" "name" "score"
printf "%-10s|%10d|\n" "alice" 90
printf "%-10s|%10d|\n" "bob" 8

Output

name      |     score|
alice     |        90|
bob       |         8|

- left-aligns, the number is the minimum width, padded with spaces. Far more reliable than padding with echo.

Bash

printf "%s\n" one two three
printf "[%s] " a b c; echo

Output

one
two
three
[a] [b] [c]

Bash

printf "%05d\n" 42
printf "%+d %+d\n" 5 -5
printf "%.1f%%\n" 99.55

Output

00042
+5 -5
99.6%

% is special in the format string; write %% for a literal percent. Forgetting it garbles generated nginx or cron files.

Bash

printf "hello %s\n" "world"
printf "%d + %d = %d\n" 2 3 5
printf "%.2f\n" 3.14159
printf "%x %X\n" 255 255

Output

hello world
2 + 3 = 5
3.14
ff FF

Bash

printf "%-10s|%10s|\n" "name" "score"
printf "%-10s|%10d|\n" "alice" 90
printf "%-10s|%10d|\n" "bob" 8

Output

name      |     score|
alice     |        90|
bob       |         8|

- 表示左对齐，数字表示最小宽度，不够补空格。做表格对齐时比 echo + 手动空格可靠得多。

Bash

printf "%s\n" one two three
printf "[%s] " a b c; echo

Output

one
two
three
[a] [b] [c]

Bash

printf "%05d\n" 42
printf "%+d %+d\n" 5 -5
printf "%.1f%%\n" 99.55

Output

00042
+5 -5
99.6%

printf 的格式串里 % 是特殊字符，要输出百分号必须写 %%。写 nginx 配置或 cron 时忘了这点，输出会错位。