printf (將參數插入用戶定義的文本字符串中，從而創建格式化的輸出)

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命令行 Unix&Linux命令 printf

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在類似Unix的操作系統上，printf命令將參數插入用戶定義的文本字符串中，從而創建格式化的輸出。

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1 printf 運行系統環境

2 printf 描述

3 printf 語法

4 printf 例子

printf 運行系統環境

Linux

printf 描述

printf將格式化的字符串打印到標準輸出。它的根源是C編程語言，它使用具有相同名稱的函數。這是從數字或文本參數產生精確格式輸出的一種便捷方法。

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printf 語法

printf FORMAT [ARGUMENT]...

printf OPTION

選件

FORMAT	FORMAT控制輸出，并定義將在輸出中表達ARGUMENT的方式。請參閱下面的“FORMA”部分。
ARGUMENT	根據FORMAT的定義，每個ARGUMENT都將插入到格式化輸出中。
- help	顯示幫助消息，然后退出。
- version	顯示版本信息，然后退出。

格式

該格式字符串包含三種類型的對象：

普通字符，將原樣復制到輸出中。
解釋的字符序列，使用反斜杠（“ \ ”）進行轉義。
轉換規范，用于定義將ARGUMENT表示為輸出一部分的方式。

這是一個使用這三種對象的快速示例：

" printf" My name is\"％s \".\ nIt's a pleasure to meet you." "John"

此命令產生輸出：

My name is "John". 
It's a pleasure to meet you.

在這里，FORMAT用雙引號（“）括起來。有一個轉換規范：％s，它將參數” John“解釋為字符串并將其插入輸出中。有三個轉義的字符序列：兩次出現\ “和\ n出現一次。序列\“轉換為文字雙引號；以反斜杠轉義，以便printf知道將其視為文字字符而不是FORMAT字符串的結尾。\ n是換行符的序列，并告訴printf 開始新的一行并從那里繼續輸出。

的功率的printf就在于，對于任何給定的格式字符串，則ARGUMENT s時，可以改變影響輸出。例如，可以僅通過更改參數“ John”來更改以上示例中命令的輸出。如果在腳本中使用，則此參數可以設置為變量。例如，命令

printf "Hi, I'm %s. \s. \n" $ LOGNAME

...將插入環境變量 $ LOGNAME的值，該值是運行命令的人的用戶名。

轉換規格

每個轉換規范都以％開頭，以轉換字符結尾。在％和轉換字符之間可能有以下順序：

-	減號。這告訴printf向左調整參數的轉換。
number	一個整數，它指定字段的寬度；printf將在至少數字字符寬的字段中打印ARGUMENT的轉換。如有必要，將在左側填充（或在需要進行左調整的情況下在右側填充）以填充字段寬度。
.	一個周期，它將字段寬度與精度分開。
number	整數，精度，它指定要從字符串中打印的最大字符數，或者浮點值的小數點后的位數，或者整數的最小位數。
h or l	它們分別區分短整數和長整數，通常僅在計算機編程時才需要。

轉換字符本身（告訴printf需要什么樣的參數）如下：

轉換字符	參數類型
d，i	整數，表示為十進制數。
o	整數，表示為無符號八進制數。
x，X	整數，表示為無符號十六進制數
u	整數，表示為無符號十進制數。
c	整數，表示為字符。整數對應于字符的ASCII碼。
s	一個字符串。
F	浮點數，默認精度為6。
e，E	以科學計數法表示的浮點數，默認精度為6。
p	內存地址指針。
％	沒有轉換；而是打印文字百分號（“ ％ ”）。

寬度或精度可以用星號（“ * ”）表示；如果是這樣，星號將讀取一個必須為整數的參數，并使用該值。例如，

printf "%.* s" 5 "abcdefg"

...產生以下輸出：

abcde

下表說明了printf使用各種FORMAT字符串輸出其ARGUMENT（“ computerhope ”）的方式。每個字符串都用引號引起來，以便更輕松地查看每個字符串的確切范圍：

格式字符串	參數字符串	輸出字符串
“％s”	“computerhope”	“computerhope”
“％8s”	“computerhope”	“computerhope”
“％.8s”	“computerhope”	“computer”
“％-8s”	“computerhope”	“computerhope”
“％-15s”	“computerhope”	“computerhope”
“％15.8s”	“computerhope”	“computer”
“％-15.8”	“computerhope”	“computer”
“％-15.2”	“computerhope”	“ co”

請注意，printf要求轉換字符串的數量與ARGUMENT的數量相匹配。它一對一地映射它們，并期望為每個轉換字符串找到一個準確的ARGUMENT。唯一的例外是使用星號的轉換字符串。這樣的字符串每個都需要兩個參數。

轉換字符串始終從左向右解釋。例如，以下printf命令：

“ printf”％d puls ％5f％s％。* f。5 5.05“equals” 3 10.05

...產生以下輸出：

5 plus 5.050000 equals 10.050。

解釋的轉義字符序列

以下字符序列由printf解釋為特殊字符：

\“	打印雙引號（“）
\\	打印反斜杠（\）
\a	發出警報（按鈴）
\b	打印退格鍵
\c	指示printf不產生進一步的輸出
\e	打印轉義字符（ASCII代碼27）
\f	打印換頁
\n	打印換行符
\r	打印回車
\t	打印水平標簽
\v	打印垂直標簽
\NNN	打印八進制值NNN（1到3位數字）的字節
\xHH	打印一個十六進制值HH（1到2位數字）的字節
\uHHHH	打印具有十六進制值HHHH（4位）的Unicode字符
\UHHHHHHHH	打印具有十六進制值HHHHHHHH（8位）的Unicode字符
％b	將ARGUMENT打印為帶有“ \ ”轉義符的字符串，其解釋如上所列，但八進制轉義符的格式為\ 0或\ 0 NN

殼牌行情

注意您的外殼解釋帶引號的字符串的方式。如果您的外殼無法正確解釋帶引號的字符串，請嘗試使用單引號而不是雙引號。

printf FORMAT [ARGUMENT]...

printf OPTION

Options

FORMAT	FORMAT controls the output, and defines the way that the ARGUMENTs will be expressed in the output. See the Format section, below.
ARGUMENT	Each ARGUMENT will be inserted into the formatted output according to the definition of FORMAT.
--help	Display a help message, and exit.
--version	Display version information, and exit.

Format

The FORMAT string contains three types of objects:

ordinary characters, which are copied verbatim to the output.
interpreted character sequences, which are escaped with a backslash ("\").
conversion specifications, which define the way in which ARGUMENTs will be expressed as part of the output.

Here is a quick example which uses these three types of objects:

printf "My name is \"%s\".\nIt's a pleasure to meet you." "John"

This command produces the output:

My name is "John".
It's a pleasure to meet you.

Here, FORMAT is enclosed in double-quotes ("). There is one conversion specification: %s, which interprets the argument "John" as a string and inserts it into the output. There are three escaped character sequences: two occurrences of \" and one occurrence of \n. The sequence \" translates as a literal double-quote; it is escaped with a backslash so that printf knows to treat it as a literal character, and not as the end of the FORMAT string. \n is the sequence for a newline character, and tells printf to begin a new line and continue the output from there.

The power of printf lies in the fact that for any given FORMAT string, the ARGUMENTs can be changed to affect the output. For example, the output of the command in the above example can be altered just by changing the argument, "John". If used in a script, this argument can be set to a variable. For instance, the command

printf "Hi, I'm %s.\n" $LOGNAME

...will insert the value of the environment variable $LOGNAME, which is the username of whoever ran the command.

Conversion Specifications

Each conversion specification begins with a % and ends with a conversion character. Between the % and the conversion character there may be, in order:

-	A minus sign. This tells printf to left-adjust the conversion of the argument.
number	An integer that specifies field width; printf will print a conversion of ARGUMENT in a field at least number characters wide. If necessary it will be padded on the left (or right, if left-adjustment is called for) to make up the field width.
.	A period, which separates the field width from the precision.
number	An integer, the precision, which specifies the maximum number of characters to be printed from a string, or the number of digits after the decimal point of a floating-point value, or the minimum number of digits for an integer.
h or l	These differentiate between a short and a long integer, respectively, and are generally only needed for computer programming.

The conversion characters themselves, which tell printf what kind of argument to expect, are as follows:

conversion character	argument type
d, i	An integer, expressed as a decimal number.
o	An integer, expressed as an unsigned octal number.
x, X	An integer, expressed as an unsigned hexadecimal number
u	An integer, expressed as an unsigned decimal number.
c	An integer, expressed as a character. The integer corresponds to the character's ASCII code.
s	A string.
f	A floating-point number, with a default precision of 6.
e, E	A floating-point number expressed in scientific notation, with a default precision of 6.
p	A memory address pointer.
%	No conversion; a literal percent sign ("%") is printed instead.

A width or precision may be represented with an asterisk ("*"); if so, the asterisk reads in an argument, which must be an integer, and uses that value. For example,

printf "%.*s" 5 "abcdefg"

...produces the following output:

abcde

The following table represents the way that printf would output its ARGUMENT, "computerhope", using various FORMAT strings. Each string is enclosed in quotes so that it's easier to see the exact extent of each:

FORMAT string	ARGUMENT string	output string
"%s"	"computerhope"	"computerhope"
"%8s"	"computerhope"	"computerhope"
"%.8s"	"computerhope"	"computer"
"%-8s"	"computerhope"	"computerhope"
"%-15s"	"computerhope"	"computerhope"
"%15.8s"	"computerhope"	"computer"
"%-15.8"	"computerhope"	"computer"
"%-15.2"	"computerhope"	"co "

Please note that printf requires the number of conversion strings to match the number of ARGUMENTs; it maps them one-to-one, and expects to find exactly one ARGUMENT for each conversion string. The only exception is a conversion string which uses an asterisk; such strings require two arguments each.

Conversion strings are always interpreted from left to right. For example, the following printf command:

printf "%d plus %5f %s %.*f." 5 5.05 "equals" 3 10.05

...produces the following output:

5 plus 5.050000 equals 10.050.

Interpreted Escaped Character Sequences

The following character sequences are interpreted as special characters by printf:

\"	prints a double-quote (")
\\	prints a backslash (\)
\a	issues an alert (plays a bell)
\b	prints a backspace
\c	instructs printf to produce no further output
\e	prints an escape character (ASCII code 27)
\f	prints a form feed
\n	prints a newline
\r	prints a carriage return
\t	prints a horizontal tab
\v	prints a vertical tab
\NNN	prints a byte with octal value NNN (1 to 3 digits)
\xHH	prints a byte with hexadecimal value HH (1 to 2 digits)
\uHHHH	prints the unicode character with hexadecimal value HHHH (4 digits)
\UHHHHHHHH	prints the unicode character with hexadecimal value HHHHHHHH (8 digits)
%b	prints ARGUMENT as a string with "\" escapes interpreted as listed above, with the exception that octal escapes take the form \0 or \0NN

Quoting In The Shell

Be careful with the way your shell interprets quoted strings. If your shell is not interpreting your quoted string correctly, try using single-quotes rather than double-quotes.

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printf 例子

printf 'hello\nworld\n!'

打印以下輸出：

hello 
world 
!

printf "%b" 'hello\nworld\n!'

打印與上述示例相同的輸出。

printf "Your home folder is %s.\n" $HOME

打印一個字符串，告訴您主目錄的位置。

printf 'hello\nworld\n!'

Prints the following output:

hello 
world 
!

printf "%b" 'hello\nworld\n!'

Prints the same output as the above example.

printf "Your home folder is %s.\n" $HOME

Prints a string telling you the location of your home directory.

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其他命令行

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