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:

2. # format-string is double quotes
4. $ printf "%d%s\ n" 1 "abc"
6. 1 ABC
8. # single quotes are the same as double quotes
10. $ printf '%d%s\ n' 1 "abc"
12. 1 ABC
14. # No quotation marks can also be output
16. $ printf %s abcdef
18. ABCdef
20. # The format specifies only one parameter, but the extra parameter is still output in that format, format-string is reused
22. $ printf %s ABC def
24. ABCdef
26. $ printf "%s\ n" abc def
28. Abc
30. Def
32. $ printf "%s%s%s\ n" A b c D e F g h i j
34. A b C
36. D E F
38. G h I
40. J
42. # If there is no arguments, then%s is replaced with NULL,%d replaces with 0
44. $ printf "%s and%d \ n"
46. and 0
48. # 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
50. $ printf "The first program always prints '%s,%d\ n'" Hello Shell
52. -bash: printf: Shell: Invalid number
54. The first program is always prints ' hello,0 '
56. $

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 in bash, ksh93, and zsh support floating-point format

Shell printf Command: Format output statement