【Bash百宝箱】shell内建命令之echo、printf
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【Bash百宝箱】shell内建命令之echo、printf
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原文地址：http://blog.csdn.net/iEearth/article/details/52640972
1、echo
在shell中，內(nèi)建（builtin）命令echo，格式如下：
echo [-neE] [arg ...]- 1
echo命令用于輸出各參數(shù)arg，參數(shù)間以空格分隔，結(jié)尾是個(gè)換行符。選項(xiàng)“-n”禁止輸出結(jié)尾的換行符。對(duì)于一些反斜線“\”轉(zhuǎn)義的特殊字符，在echo命令中默認(rèn)不進(jìn)行轉(zhuǎn)義，選項(xiàng)“-e”啟用轉(zhuǎn)義，“-E”禁止轉(zhuǎn)義。
下面是反斜線“\”轉(zhuǎn)義的特殊字符。
\a 警告（響鈴）\b 退格刪除\c 禁止繼續(xù)輸出\e 轉(zhuǎn)義字符\E 轉(zhuǎn)義字符\f 換頁(yè)\n 新行\r 換行\t 水平制表符\v 垂直制表符\\ 反斜線\0nnn 八進(jìn)制數(shù)nnn表示的八位字符\xHH 十六進(jìn)制數(shù)HH表示的八位字符\uHHHH 一到四個(gè)十六進(jìn)制數(shù)表示的Unicode字符\UHHHHHHHH 一到八個(gè)十六進(jìn)制數(shù)表示的Unicode字符- 1
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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- 1
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2、printf
在shell中，內(nèi)建（builtin）命令printf，格式如下：
printf [-v var] format [arguments]- 1
printf命令用于把格式化的參數(shù)arguments打印到標(biāo)準(zhǔn)輸出，格式由參數(shù)format控制。如果指定了選項(xiàng)“-v var”，結(jié)果會(huì)保存到變量var中，而非打印到標(biāo)準(zhǔn)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(biāo)準(zhǔn)輸出。第二種是轉(zhuǎn)義字符序列，先轉(zhuǎn)義后打印到標(biāo)準(zhǔn)輸出。第三種是格式控制字符串，與后面的參數(shù)arguments對(duì)應(yīng)。
格式控制有以下幾種形式：
\" 雙引號(hào)\\ 反斜線\a 警告（響鈴）\b 退格刪除\c 禁止繼續(xù)輸出\e 轉(zhuǎn)義字符\f 分頁(yè)\n 新行\r 換行\t 水平制表符\v 垂直制表符\NNN 八進(jìn)制數(shù)\xHH 十六進(jìn)制數(shù)\uHHHH 十六進(jìn)制Unicode\UHHHHHHHH 十六進(jìn)制Unicode%% 百分號(hào)%b 擴(kuò)展printf中參數(shù)arguments的反斜線轉(zhuǎn)義序列，但“\c”例外，“\'”、“\"”和“\?”中的反斜線也不會(huì)去掉，而且以“\0”開(kāi)頭的八進(jìn)制數(shù)可能包含四個(gè)數(shù)字。%q 把對(duì)應(yīng)參數(shù)arguments以能夠重新作為shell輸入的格式打印出來(lái)。%(datefmt)T 以格式datefmt輸出日期，對(duì)應(yīng)的參數(shù)argument為從1970年1月1日開(kāi)始的秒數(shù)，有兩個(gè)特殊的參數(shù)，-1表示當(dāng)前時(shí)間，-2表示shell運(yùn)行時(shí)間，默認(rèn)為-1。- 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.- 1
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對(duì)于標(biāo)準(zhǔn)C中printf函數(shù)的轉(zhuǎn)換字符，百分號(hào)后跟“diouxXfeEgGcs”中的任意一個(gè)字符，在printf命令中也可以使用，而且標(biāo)準(zhǔn)C中printf函數(shù)的輸出樣式控制標(biāo)記、輸出字符串寬度、數(shù)字精度等也適用于printf命令。下面以例子說(shuō)明。
打印十六進(jìn)制整數(shù)：
$ printf "%x\n" 17 11 $ printf "%X\n" 17 11 $ printf "%#x\n" 17 0x11 $ printf "%#X\n" 17 0X11- 1
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設(shè)置輸出字符串寬度和對(duì)齊方式：
$ printf "%d\n" 123 123 $ printf "%6d\n" 123123 $ printf "%-6d\n" 123 123- 1
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設(shè)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- 1
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在正數(shù)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- 1
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在正數(shù)前面添加加號(hào)：
$ printf "%d\n" 123 123 $ printf "%+d\n" 123 +123 $ printf "%d\n" -123 -123 $ printf "%+d\n" -123 -123- 1
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設(shè)置數(shù)字輸出格式為千分位：
$ printf "%d\n" 123456789 123456789 $ printf "%'d\n" 123456789 123,456,789- 1
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設(shè)置浮點(diǎn)數(shù)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總結(jié)
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