Shell Script Learning 15 Shell printf command: Format output statement

The printf command is used to format the output and is an enhanced version of the echo command. It is a finite variant of the C-language printf () library function, and is somewhat different in syntax.

Note: printf is defined by the POSIX standard, and portability is better than echo.

As with the echo command, the printf command can also output a simple string:

1. $printf "Hello, Shell\ n"
2. Hello, Shell
3. $

printf does not wrap like echo, and you must explicitly add a line break (\ n).

The syntax of the printf command:

printf format-string [arguments ...]

Format-string is the format control string and arguments is the parameter list.

printf () has been described in the C-language introductory tutorial, features and usage similar to the printf command, see: C-Format output function printf ()

This is only a description of the difference from the C-language printf () function:

• printf command without parentheses
• Format-string can be without quotation marks, but it is best to add single quotes and double quotes.
• When the parameter is more than the format control (%), format-string can be reused and all parameters can be converted.
• Arguments use spaces separated by commas.

Take a look at the following example:

1. # format-string is double quotes
2. $ printf "%d%s\ n" 1 "abc"
3. 1 ABC
4. # single quotes are the same as double quotes
5. $ printf '%d%s\ n' 1 "abc"
6. 1 ABC
7. # No quotation marks can also be output
8. $ printf %s abcdef
9. ABCdef
10. # The format specifies only one parameter, but the extra parameter is still output in that format, format-string is reused
11. $ printf %s ABC def
12. ABCdef
13. $ printf "%s\ n" abc def
14. Abc
15. Def
16. $ printf "%s%s%s\ n" A b c D e F g h i j
17. A b C
18. D E F
19. G h I
20. J
21. # If there is no arguments, then%s is replaced with NULL,%d replaces with 0
22. $ printf "%s and%d \ n"
23. and 0
24. # If the string is displayed in%d format, then there will be a warning indicating an invalid number, at which point the default is 0
25. $ printf "The first program always prints '%s,%d\ n'" Hello Shell
26. -bash: printf: Shell: Invalid number
27. The first program is always prints ' hello,0 '
28. $

Note that, according to the POSIX standard, floating-point formats%E,%E,%f,%g, and%g are "No need to be supported." This is because awk supports floating-point budgeting and has its own printf statement. In this way, a small awk program can be used to print a floating-point value in a shell program. However, the printf commands built into bash, ksh93, and zsh support floating-point formatting.

Shell Script Learning 15 Shell printf command: Format output statement