【Bash百宝箱】shell内建命令之echo、printf

港控/mmm° 2022-07-15 23:45 244阅读 0赞

## 1、echo ##

在shell中，内建（builtin）命令echo，格式如下：

echo [-neE] [arg ...]

echo命令用于输出各参数arg，参数间以空格分隔，结尾是个换行符。选项“-n”禁止输出结尾的换行符。对于一些反斜线“\\”转义的特殊字符，在echo命令中默认不进行转义，选项“-e”启用转义，“-E”禁止转义。

下面是反斜线“\\”转义的特殊字符。

\a     警告（响铃）
                  \b     退格删除
                  \c     禁止继续输出
                  \e     转义字符
                  \E     转义字符
                  \f     换页
                  \n     新行
                  \r     换行
                  \t     水平制表符
                  \v     垂直制表符
                  \\     反斜线
                  \0nnn  八进制数nnn表示的八位字符
                  \xHH   十六进制数HH表示的八位字符
                  \uHHHH  一到四个十六进制数表示的Unicode字符
                  \UHHHHHHHH  一到八个十六进制数表示的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，内建（builtin）命令printf，格式如下：

printf [-v var] format [arguments]

printf命令用于把格式化的参数arguments打印到标准输出，格式由参数format控制。如果指定了选项“-v var”，结果会保存到变量var中，而非打印到标准输出。

格式format有三种形式。第一种是原始字符串，直接打印到标准输出。第二种是转义字符序列，先转义后打印到标准输出。第三种是格式控制字符串，与后面的参数arguments对应。

格式控制有以下几种形式：

\"     双引号
           \\     反斜线
           \a     警告（响铃）
           \b     退格删除
           \c     禁止继续输出
           \e     转义字符
           \f     分页
           \n     新行
           \r     换行
           \t     水平制表符
           \v     垂直制表符
           \NNN   八进制数
           \xHH   十六进制数
           \uHHHH  十六进制Unicode
           \UHHHHHHHH  十六进制Unicode
           %% 百分号
           %b 扩展printf中参数arguments的反斜线转义序列，但“\c”例外，“\'”、“\"”和“\?”中的反斜线也不会去掉，而且以“\0”开头的八进制数可能包含四个数字。
           %q 把对应参数arguments以能够重新作为shell输入的格式打印出来。
           %(datefmt)T 以格式datefmt输出日期，对应的参数argument为从1970年1月1日开始的秒数，有两个特殊的参数，-1表示当前时间，-2表示shell运行时间，默认为-1。

上面提到的日期格式如下（摘录自“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.

对于标准C中printf函数的转换字符，百分号后跟“diouxXfeEgGcs”中的任意一个字符，在printf命令中也可以使用，而且标准C中printf函数的输出样式控制标记、输出字符串宽度、数字精度等也适用于printf命令。下面以例子说明。

打印十六进制整数：

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

设置输出字符串宽度和对齐方式：

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

设置输出字符串宽度和填充方式：

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

在正数前面添加空格：

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

在正数前面添加加号：

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

设置数字输出格式为千分位：