原文地址：http://blog.csdn.net/iEearth/article/details/52640972

1、echo

在shell中，內建（builtin）命令echo，格式如下：

echo [-neE] [arg ...]

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echo命令用于輸出各參數arg，參數間以空格分隔，結尾是個換行符。選項“-n”禁止輸出結尾的換行符。對于一些反斜線“\”轉義的特殊字符，在echo命令中默認不進行轉義，選項“-e”啟用轉義，“-E”禁止轉義。

下面是反斜線“\”轉義的特殊字符。

\a 警告（響鈴）\b 退格刪除\c 禁止繼續輸出\e 轉義字符\E 轉義字符\f 換頁\n 新行\r 換行\t 水平制表符\v 垂直制表符\\ 反斜線\0nnn 八進制數nnn表示的八位字符\xHH 十六進制數HH表示的八位字符\uHHHH 一到四個十六進制數表示的Unicode字符\UHHHHHHHH 一到八個十六進制數表示的Unicode字符

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例子如下：

$ echo "a\tb" a\tb $ echo -e "a\tb" a b $ echo -E "a\tb" a\tb

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2、printf

在shell中，內建（builtin）命令printf，格式如下：

printf [-v var] format [arguments]

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printf命令用于把格式化的參數arguments打印到標準輸出，格式由參數format控制。如果指定了選項“-v var”，結果會保存到變量var中，而非打印到標準輸出。

格式format有三種形式。第一種是原始字符串，直接打印到標準輸出。第二種是轉義字符序列，先轉義后打印到標準輸出。第三種是格式控制字符串，與后面的參數arguments對應。

格式控制有以下幾種形式：

\" 雙引號\\ 反斜線\a 警告（響鈴）\b 退格刪除\c 禁止繼續輸出\e 轉義字符\f 分頁\n 新行\r 換行\t 水平制表符\v 垂直制表符\NNN 八進制數\xHH 十六進制數\uHHHH 十六進制Unicode\UHHHHHHHH 十六進制Unicode%% 百分號%b 擴展printf中參數arguments的反斜線轉義序列，但“\c”例外，“\'”、“\"”和“\?”中的反斜線也不會去掉，而且以“\0”開頭的八進制數可能包含四個數字。%q 把對應參數arguments以能夠重新作為shell輸入的格式打印出來。%(datefmt)T 以格式datefmt輸出日期，對應的參數argument為從1970年1月1日開始的秒數，有兩個特殊的參數，-1表示當前時間，-2表示shell運行時間，默認為-1。

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上面提到的日期格式如下（摘錄自“man 3 strftime”）：

%a The abbreviated name of the day of the week according to the current locale.%A The full name of the day of the week according to the current locale.%b The abbreviated month name according to the current locale.%B The full month name according to the current locale.%c The preferred date and time representation for the current locale.%C The century number (year/100) as a 2-digit integer. (SU)%d The day of the month as a decimal number (range 01 to 31).%D Equivalent to %m/%d/%y. (Yecch—for Americans only. Americans should note that in other countries %d/%m/%y is rather common. This means that in international context this format isambiguous and should not be used.) (SU)%e Like %d, the day of the month as a decimal number, but a leading zero is replaced by a space. (SU)%E Modifier: use alternative format, see below. (SU)%F Equivalent to %Y-%m-%d (the ISO 8601 date format). (C99)%G The ISO 8601 week-based year (see NOTES) with century as a decimal number. The 4-digit year corresponding to the ISO week number (see %V). This has the same format and value as %Y,except that if the ISO week number belongs to the previous or next year, that year is used instead. (TZ)%g Like %G, but without century, that is, with a 2-digit year (00-99). (TZ)%h Equivalent to %b. (SU)%H The hour as a decimal number using a 24-hour clock (range 00 to 23).%I The hour as a decimal number using a 12-hour clock (range 01 to 12).%j The day of the year as a decimal number (range 001 to 366).%k The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank. (See also %H.) (TZ)%l The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a blank. (See also %I.) (TZ)%m The month as a decimal number (range 01 to 12).%M The minute as a decimal number (range 00 to 59).%n A newline character. (SU)%O Modifier: use alternative format, see below. (SU)%p Either "AM" or "PM" according to the given time value, or the corresponding strings for the current locale. Noon is treated as "PM" and midnight as "AM".%P Like %p but in lowercase: "am" or "pm" or a corresponding string for the current locale. (GNU)%r The time in a.m. or p.m. notation. In the POSIX locale this is equivalent to %I:%M:%S %p. (SU)%R The time in 24-hour notation (%H:%M). (SU) For a version including the seconds, see %T below.%s The number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC). (TZ)%S The second as a decimal number (range 00 to 60). (The range is up to 60 to allow for occasional leap seconds.)%t A tab character. (SU)%T The time in 24-hour notation (%H:%M:%S). (SU)%u The day of the week as a decimal, range 1 to 7, Monday being 1. See also %w. (SU)%U The week number of the current year as a decimal number, range 00 to 53, starting with the first Sunday as the first day of week 01. See also %V and %W.%V The ISO 8601 week number (see NOTES) of the current year as a decimal number, range 01 to 53, where week 1 is the first week that has at least 4 days in the new year. See also %U and%W. (SU)%w The day of the week as a decimal, range 0 to 6, Sunday being 0. See also %u.%W The week number of the current year as a decimal number, range 00 to 53, starting with the first Monday as the first day of week 01.%x The preferred date representation for the current locale without the time.%X The preferred time representation for the current locale without the date.%y The year as a decimal number without a century (range 00 to 99).%Y The year as a decimal number including the century.%z The +hhmm or -hhmm numeric timezone (that is, the hour and minute offset from UTC). (SU)%Z The timezone name or abbreviation.%+ The date and time in date(1) format. (TZ) (Not supported in glibc2.)%% A literal '%' character.

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對于標準C中printf函數的轉換字符，百分號后跟“diouxXfeEgGcs”中的任意一個字符，在printf命令中也可以使用，而且標準C中printf函數的輸出樣式控制標記、輸出字符串寬度、數字精度等也適用于printf命令。下面以例子說明。

打印十六進制整數：

$ printf "%x\n" 17 11 $ printf "%X\n" 17 11 $ printf "%#x\n" 17 0x11 $ printf "%#X\n" 17 0X11

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設置輸出字符串寬度和對齊方式：

$ printf "%d\n" 123 123 $ printf "%6d\n" 123123 $ printf "%-6d\n" 123 123

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設置輸出字符串寬度和填充方式：

$ printf "%d\n" 123 123 $ printf "%6d\n" 123123 $ printf "%06d\n" 123 000123

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在正數前面添加空格：

$ printf "%d\n" 123 123 $ printf "% d\n" 123123 $ printf "%d\n" -123 -123 $ printf "% d\n" -123 -123

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在正數前面添加加號：

$ printf "%d\n" 123 123 $ printf "%+d\n" 123 +123 $ printf "%d\n" -123 -123 $ printf "%+d\n" -123 -123

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設置數字輸出格式為千分位：

$ printf "%d\n" 123456789 123456789 $ printf "%'d\n" 123456789 123,456,789

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設置浮點數精度：

$ printf "%f\n" 123 123.000000 $ printf "%.f\n" 123 123 $ printf "%.1f\n" 123 123.0 $ printf "%.3f\n" 123 123.000

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