文章出處
1、echo
在shell中，內建（builtin）命令echo，格式如下：
echo [-neE] [arg ...]
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
例子如下：
$ echo "a\tb"a\tb$ echo -e "a\tb"a b$ echo -E "a\tb"a\tb
2、printf
在shell中，內建（builtin）命令printf，格式如下：
printf [-v var] format [arguments]
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。
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 is ambiguous 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.
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" 1711$ printf "%X\n" 1711$ printf "%#x\n" 170x11$ printf "%#X\n" 170X11
設置輸出字符串寬度和對齊方式：
$ printf "%d\n" 123123$ printf "%6d\n" 123 123$ printf "%-6d\n" 123123
設置輸出字符串寬度和填充方式：
$ printf "%d\n" 123123$ printf "%6d\n" 123 123$ printf "%06d\n" 123000123
在正數前面添加空格：
$ printf "%d\n" 123123$ printf "% d\n" 123 123$ printf "%d\n" -123-123$ printf "% d\n" -123-123
在正數前面添加加號：
$ printf "%d\n" 123123$ printf "%+d\n" 123+123$ printf "%d\n" -123-123$ printf "%+d\n" -123-123
設置數字輸出格式為千分位：
$ printf "%d\n" 123456789123456789$ printf "%'d\n" 123456789123,456,789
設置浮點數精度：
$ printf "%f\n" 123123.000000$ printf "%.f\n" 123123$ printf "%.1f\n" 123123.0$ printf "%.3f\n" 123123.000
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