Printf – store formatted string output in a variable

bashprintfvariablevariable substitution

Instead of the following

printf '%s\t%s\t%s\t%s\n' 'index' 'podcast' 'website' 'YouTube'

I want to store the printf output in a Results variable, how can I do this?

Best Answer

Bash (since 3.1), zsh (since 5.3) and ksh93 (since v- and u+m 2021-11-28) have an "assignment to variable option" for printf:

$ Row='%s\t%s\t%s\t%s\n'
$ printf -v Result -- "${Row}" 'index' 'podcast' 'website' 'YouTube'
$ echo "${Result}"
index   podcast website YouTube

$

Notice I get two newlines -- one from the printf format, the other from the echo.

You could also control the column widths using something like $-10s for each field, instead of tabbing.

The advantage of this over the $( ... ) or `back-quote` syntax, in addition to preserving trailing newlines is that it does not need to run a subshell for the assignment which in shells other than ksh93¹ is relatively costly.

^{¹ It's less costly in ksh93 where it doesn't involve a fork but can be made even less so there with the ${ printf...; } form of substitution. That one will be supported in the next version of bash after 5.2.x as well as the next version of zsh after 5.9.x as well as the ${|...} variant from mksh}

Related Solutions

Bash – Using Dashes in Printf

The -- is used to tell the program that whatever follows should not be interpreted as a command line option to printf.

Thus the printf "--" you tried basically ended up as "printf with no arguments" and therefore failed.

Bash prevent printf from interrupting another printf

In fact you need a mutex :

Each sub-shell will access concurrently to the same /dev/stdout of the parent shell, so you can not ensure the order even inside the same function. To ensure it you need a lock which enforce the mutual exclusion i.e. : all other processes won't start to write in /dev/stdout until the lock is released.

#!/bin/bash

function foo {
lockdir=/tmp/myscript.lock
 mkdir "$lockdir" 2>/dev/null
while [ $? -ne 0 ]; do mkdir "$lockdir" 2>/dev/null; done
printf "Test line break: $1\nafter line break: $1\n\n"
rm -rf $lockdir
}

for VARIABLE in {1..30}
do
  foo $VARIABLE &
done
wait

This will give this as a result :

$ bash plop1 2>/dev/null
Test line break: 5
after line break: 5

Test line break: 3
after line break: 3

Test line break: 11
after line break: 11

Test line break: 23
after line break: 23

Test line break: 14
after line break: 14

Test line break: 17
after line break: 17

Test line break: 24
after line break: 24

Test line break: 21
after line break: 21

Test line break: 27
after line break: 27

Test line break: 6
after line break: 6

Test line break: 2
after line break: 2

Test line break: 9
after line break: 9

Test line break: 26
after line break: 26

Test line break: 29
after line break: 29

Test line break: 20
after line break: 20

Test line break: 1
after line break: 1

Test line break: 12
after line break: 12

Test line break: 4
after line break: 4

Test line break: 13
after line break: 13

Test line break: 10
after line break: 10

Test line break: 15
after line break: 15

Test line break: 28
after line break: 28

Test line break: 25
after line break: 25

Test line break: 19
after line break: 19

Test line break: 18
after line break: 18

Test line break: 8
after line break: 8

Test line break: 7
after line break: 7

Test line break: 16
after line break: 16

Test line break: 22
after line break: 22

Test line break: 30
after line break: 30

Best Answer

Related Solutions

Bash – Using Dashes in Printf

Bash prevent printf from interrupting another printf

Related Question