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Today, the editor will share with you the relevant knowledge points about how to use the printf command of Linux. The content is detailed and the logic is clear. I believe most people still know too much about this knowledge, so share this article for your reference. I hope you can get something after reading this article. Let's take a look.

The common Linux command printf command imitates the printf () function in C language. The main function is to output text, according to the format we specify.

Printf formats and outputs the results.

Directory bash built-in command

Commands in GNU coreutils

Built-in command summary printf [- v var] format [arguments] main purpose formatting parameters and output.

Option-v var: output the result to the variable var instead of to standard output. Parameter format: output format.

Arguments: one or more parameters.

Escape sequences: in addition to supporting printf (1) and printf (3) escape sequences, the built-in printf also supports the following escape sequences: backslash escape characters in the% b expansion parameter. % Q expands the parameter to use as shell input. % (fmt) T outputs a date-time string based on the escape characters in strftime (3). The return status is successful unless an illegal option, write error, or assignment error is given.

Example #%-5s format is left-aligned and width 5 string instead ('- 'means left-aligned), if not used, right-aligned by default. The #%-4.2f format has a left-aligned width of 4, retaining two decimal places. Printf "%-5s%-10s%-4s\ n" NO Name Mark printf "%-5s%-10s%-4.2f\ n" 01 Tom 90.3456 printf "%-5s%-10s%-4.2f\ n" 02 Jack 89.2345 printf "%-5s%-10s%-4.2f\ n" 03 Jeff 98.4323 # output NO Name Mark 01 Tom 90.35 02 Jack 89.23 03 Jeff 98.43 #% b% Q% (fmt) T example # see it again with a newline. Printf "% s\ n" 'hello world' # expands the newline character, as shown above. Printf "% b" 'hello world\ n' printf'% Q\ n' a b c'# output a\ b\ c #% z is the time zone and% n is the newline character. Printf "% (% F% T% z% n) T" # output 2019-09-10 01:48:07 + 0000 Note this command is a bash built-in command, please see the help command for help.

External command summary printf FORMAT [ARGUMENT]. The main purpose of printf OPTION is to format parameters and output.

Option-help displays help and exits. -- version displays version information and exits. Parameter format: output format.

Arguments: one or more parameters.

Omitted here (% b% Q), if the version of coreutils you installed supports them, please refer to the example above. Supported escape sequence:\ "double quotation marks\\ backslash\ a bell\ b backspace\ c truncated output\ e exit\ f page flip\ nnewline\ r return\ t horizontal tab\ v Vertical tabs\ NNN octal numbers (1 to 3 digits)\ xHH hexadecimal numbers (1 to 2 digits)\ uHHHH Unicode characters with 4 hexadecimal digits\ UHHHHHHHH Unicode characters with 8 hexadecimal digits%% sign and C format specification for an ending in 'diouxXfeEgGcs' Will be converted to the correct type and handle variable width. Example # use / usr/bin/printf to ensure that you are not calling a built-in command. # of course, if you close the built-in printf and confirm that there is no printf function in the current environment, you can use printf directly, as shown in the link "Note" at the end. # print the subscripts and values of arrays and associative arrays by row. # declare an array without adding 'declare-a' or 'local-a' (local variables declared within the function). Arr= ('line1'' line2') / usr/bin/printf "% s\ n" ${! arr [@]} # output subscript 0 1 / usr/bin/printf "% s\ n" ${arr [@]} # output value line1 line2 # declares that associative arrays (that is, dictionaries) must add 'declare-A' or 'local-A' (local variables declared in the function). Declare-An assoc_arr= (['key1'] =' value1' ['key2'] =' value2') / usr/bin/printf "% s\ n" ${! assoc_arr [@]} # output key. Key2 key1 / usr/bin/printf "% s\ n" ${assoc_arr [@]} # output value. The return status of value2 value1 is successful unless an illegal option is given.

Note that this command is a command in the GNU coreutils package. For help, please see man-s 1 printf or info coreutils' pwd invocation'.

To start or close the built-in command, please see the enable command, and for the priority of the same name, see the discussion in the examples section of the builtin command.

Through my communication with bug-bash@gnu.org, I got an explanation of these format specifiers% b% Q% (fmt) T:

The% b format specifier in printf (1) is an additional POSIX feature in addition to the formats supported by printf (3).

The% Q and% T specifiers are non-standard and are not supported by all independently implemented printf.

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