Difference between revisions of "Printf bash builtin"

Latest revision as of 13:49, 9 February 2014

The printf command is one of a set of Bash Builtin Commands. It provides a method to print pre-formatted text, expanding shells script standard output over the echo command. See format and example below:

 printf <FORMAT> <ARGUMENTS...>
 printf "Last name: %s\nName: %s\n" "$SURNAME" "$LASTNAME"

printf does not automatically line feed unlike the echo command. LF is not implied, it must be stated. See two equivalents below:

 echo "Hello World"
 printf "Hello World\n"
 printf "%s\n" "Hello World" 

Use of %s formatting argument will also allow it to be applied to multiple lines. The following example will output a linefeed for each of the lines in the printf statement.

 printf "%s\n" "I have eaten" "the plums" "that were in" "the icebox"

The format is a character string which contains three types of objects: plain characters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument. In addition to the standard printf, `%b' causes printf to expand backslash escape sequences in the corresponding argument, and `%q' causes printf to output the corresponding argument in a format that can be reused as shell input. To print a literal % (percent-sign), use %% in the format string. Every format specifier expects an associated argument. If the format requires more arguments than are supplied, the extra format specifications behave as if a zero value or null string.

The following outputs 2 colums of text seperated by tabs. There is an initial tab, then text, tab, text and linefeed for each line. Column alignment is only achieved in this case due to the character length of string 1 and 3. This is not a way to commit columns.

 printf "%s\t%s\n" "cannoli" "bizcocho" "croissants" "eclair"

The next example will create rigid columns of text without regards to the string length so long as the string doesn't exceed the column cell allocation. It will also assign two formatting variables to contain all the arguments for the sake of readability on the printf statement lines. The vi editor will be used to place commands within a bash shell script. SHELL SCRIPT EXAMPLE:

 #/bin/bash
 #
 strHeadline===============================
 strHeadline=$strHeadline$strHeadline
 
 header="\n %-10s %8s %13s %7s\n"
 format=" %-10s %08d %10s %11.2f\n"
 
 width=43
 printf "$header" "ITEM NAME" "STOCK QTY" "DEPARTMENT" "PRICE"
 printf "%$width.${width}s\n" "$strHeadline"
 
 printf "$format" \
 cannolis 140005 bakery 20 \
 doughnuts 140049 bakery 65.656 \
 danish 140314 bakery .7 \
 sardines 110006 canned 1.59001

Breakdown of formatting arguments:

•  %-10s (line 6): string the - means format form left align over 10 spaces
•  %8d (line 7): signed decimal number with 8 places
•  %11.2f (line 7): floating point number to 9 places with 2 decimals

escape codes

format arguments

Additional arguments available to printf for formatting

•  %b Print the associated argument while interpreting backslash escapes in there
•  %q Print the associated argument shell-quoted, reusable as input
•  %d Print the associated argument as signed decimal number
•  %i Same as %d
•  %o Print the associated argument as unsigned octal number
•  %u Print the associated argument as unsigned decimal number
•  %x Print the associated argument as unsigned hexadecimal number with lower-case hex-digits (a-f)
•  %X Same as %x, but with upper-case hex-digits (A-F)
•  %f Interpret and print the associated argument as floating point number
•  %e Interpret the associated argument as double, and print it in <N>±e<N> format
•  %E Same as %e, but with an upper-case E in the printed format
•  %g Interprets the associated argument as double, but prints it like %f or %e
•  %G Same as %g, but print it like %E
•  %c Interprets the associated argument as char: only the first character of a given argument is printed
•  %s Interprets the associated argument literally as string
•  %n Assigns the number of characters printed so far to the variable named in the corresponding argument. Can't specify an array index. If the given name is already an array, the value is assigned to the zeroth element.
•  %a Interprets the associated argument as double, and prints it in the form of a C99 hexadecimal floating-point literal.
•  %A Same as %a, but print it like %E
•  %(FORMAT)T output the date-time string resulting from using FORMAT as a format string for strftime(3). The associated argument is the number of seconds since Epoch, or -1 (current time) or -2 (shell startup time). If no corresponding argument is supplies, the current time is used as default

modifiers

1. redirect Template:Sparse Entry