The Few Differences between Echo And Printf in Bash

The aim of this page📝is to understand the difference between echo and printf commands in bash for printing into the console. I have encountered this when trying to stylize an output and print out the message with tab indentation (See the SO thread, too).

Comparing with PowerShell: the difference I utilize in posh is between write-host and out-host cmdlets, the former applying .toString() the latter not handling the formatting of an object at all. Let’s go back to bash:

• echo has different versions across shells
• these versions can treat special chars and their escaping differently
• printf is the portable command for more sophisticated formatting than echo
• printf uses format string as its first argument

~                  | `echo`                    | `printf`
-------------------|---------------------------|-------------------
newline            | automatic                 | manually add `\n`
variables          | var substition `${<var>}` | format string `%s`
formatting         | unsupported               | special syntax
output to variable | unsupported               | `-v` flag

2. newlines

2.1. echo

• prints args to stdout followed by a newline

root@fba933f1c0c4:~# echo "hello"
hello

• there are 2 options for echo:
• -n suppresses the newline
• -e allows the use of escape sequences
• using these options are generally discouraged, as they are not portable

2.2. printf

• printf does not print a newline at the end by default

root@fba933f1c0c4:~# printf "hello"
helloroot@fba933f1c0c4:~# printf "hello
"
>>> hello
root@fba933f1c0c4:~#

3. variables

3.1. echo

$ var="world"
$ echo "hello ${var}"
hello world

3.2. printf

• the special char %s denotes that you expect to read that string as another argument of the command
• note that I did not add just for the sake of repetition of the previous point

$ var="world"
$ printf "hello %s" $var
hello world$

• you can also provide a list of strings as an argument that activates a loop — note how essential the newline is

$ printf "p%st" a e i o u
patpetpitpotputpkutaj$
$ printf "p%st
" a e i o u
pat
pet
pit
pot
put

• if there are >1 %s characters, printf maps them to args

$ printf "The home folder of %s is %s
" $USER $HOME
The home folder of pkutaj is /home/pkutaj

• if you put a different count of args bash will be mapping them to the count of %s in a string

h$ printf "The home folder of %s is %s
" $USER $HOME a e i
The home folder of pkutaj is /home/pkutaj
The home folder of a is e
The home folder of i is

4. formatting

4.1. printf

• the 20 after % code means that values are printed in columns that are 20 chars wid
• in the example, it pads filenames with spaces (example has files way under 20 chars of length)

$ printf "|%20s |%20s |%20s |
" $(ls)

|           b02_01.sh |           b11_01.sh |           b13_01.sh |
|           b13_04.sh |           b13_05.sh |           b13_06.sh |
|           b16_01.sh |           b21_01.sh |             b25_01/ |
|           b25_01.sh |           b27_01.sh |           b27_02.sh |
|           b43_01.sh |       bash_board.md |            hello.sh |
|           notes.txt |   shoppingnotes.txt |               test/ |

5. output to a variable

5.1. printf

$ printf -v hello "Hello %s how are you
" $USER
$ echo $hello
Hello how are you

6. links

• Echo tab characters in bash script — Stack Overflow