Shell Programming - Printf
Unix
In this tutorial we will learn about printf command in Shell Programming.
About printf
The printf command is used to print pre-formatted output. And it is similar to the printf() function of C programming language.
We can say that printf is a successor of echo command.
printf syntax
printf <format> <arguments>
Where, format is the format string used on the arguments.
format is optional and can be omitted.
Example #01
In the following example we will print name and score entered by the user.
#!/bin/sh
# take user name
printf "Enter name: "
read name
# take user score
printf "Enter score: "
read score
# display result
echo "---Result---"
printf "Name: %s\n" "$name"
printf "Score: %d\n" "$score"
Output:
$ sh example01.sh
Enter name: Yusuf Shakeel
Enter score: 8
---Result---
Name: Yusuf Shakeel
Score: 8
Where, \n prints the new line i.e., take cursor to the next line.
%s is a format for string. %d is a format for integer.
Format
Following are the format we can use for the arguments in printf command.
| Format | Description |
|---|---|
%d | For signed decimal numbers |
%i | For signed decimal numbers |
%u | For unsigned decimal numbers |
%o | For unsigned octal numbers |
%x | For unsigned hexadecimal numbers with lower case letters (a-f) |
%X | For unsigned hexadecimal numbers with upper case letters (A-F) |
%f | For floating point numbers |
%s | For string |
%% | For percent % symbol |
Modifiers
We use modifiers with format to modify output.
| Format | Description |
|---|---|
N | This specifies the width of the field for output. |
* | This is the placeholder for the width. |
- | To left align output in the field. (Default: Right align) |
0 | Pad result with leading 0s. |
+ | To put + sign before positive numbers and - sign for negative numbers. |
Example #02
In the following example we will print 100 in decimal, octal and hexadecimal form.
#!/bin/sh
num=100
# output in decimal, octal, hex form
printf "Decimal: %d\n" "$num"
printf "Octal: %o\n" "$num"
printf "Hex: %X\n" "$num"
Output:
$ sh example02.sh
Decimal: 100
Octal: 144
Hex: 64
If we want to add leading 0 for octal numbers and 0x for hex then we will add # as shown below.
#!/bin/sh
num=100
# output in decimal, octal, hex form
printf "Decimal: %d\n" "$num"
printf "Octal: %#o\n" "$num"
printf "Hex: %#X\n" "$num"
Output:
$ sh example02-1.sh
Decimal: 100
Octal: 0144
Hex: 0X64
Example #03
In the following example we will take two integer numbers from the user and divide them and show 5 decimal place.
#!/bin/sh
# get the first number
printf "Enter first integer number: "
read a
# get the second number
printf "Enter second integer number: "
read b
# if b is 0
if [ $b == 0 ]
then
printf "Division by 0 not allowed.\n"
exit # exit the script
fi
# perform division
result=`expr "$a / $b" | bc -l`
printf "%d / %d = %.5f\n" "$a" "$b" "$result"
Output:
$ sh example03.sh
Enter first integer number: 5
Enter second integer number: 2
5 / 2 = 2.50000
$ sh example03.sh
Enter first integer number: 5
Enter second integer number: 0
Division by 0 not allowed.
In the above code we are first take value of a and b from user.
Then, we are checking value of b. If b is 0 then we are printing an error message and quitting the script using exit command. And we are performing this check using the if statement.
Then, we are dividing a by b and using bc command with -l option to get decimal values and storing the result in result variable.
And then we are printing the result using the printf command.
The format is "%d / %d = %.5f\n" where, the first %d if for a, the second %d is for b.
And %.5f is for the result. Note! .5 meaning we want 5 decimal place in the result.
Example #04
In the following example we will divide a by b and we will let the user decide the number of decimal places for the result.
#!/bin/sh
# get the first number
printf "Enter first integer number: "
read a
# get the second number
printf "Enter second integer number: "
read b
# get the decimal place
printf "Enter decimal place for the result: "
read d
# if b is 0
if [ $b == 0 ]
then
printf "Division by 0 not allowed.\n"
exit # exit the script
fi
# perform division
result=`expr "$a / $b" | bc -l`
printf "%d / %d = %.*f\n" "$a" "$b" "$d" "$result"
Output:
$ sh example04.sh
Enter first integer number: 5
Enter second integer number: 2
Enter decimal place for the result: 1
5 / 2 = 2.5
$ sh example04.sh
Enter first integer number: 5
Enter second integer number: 2
Enter decimal place for the result: 3
5 / 2 = 2.500
$ sh example04.sh
Enter first integer number: 5
Enter second integer number: 2
Enter decimal place for the result: 0
5 / 2 = 2
In the above script we have %.*f in the format string. The * is replaced by the $d which tell us about the number of decimal place in the final result.
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