Formatted shell script output

Question

How can I fix the output width using printf?

This is an example script:

#!/bin/bash
OK=$(printf '\t%+50s\n' OK)
FAIL=$(printf '\t%+50s\n' FAIL)
for i in a aa aaa aaaa aaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaa; do
        echo "$i $OK"
done

Output:

a                                                       OK
aa                                                      OK
aaa                                                     OK
aaaa                                                    OK
aaaaaa                                                  OK
aaaaaaaaaaaaaaaaa                                                  OK
aaaaaaaaaaaaaaaaaaaaaaaaaa                                               OK

I want something like:

a                                                       OK
aa                                                      OK
aaa                                                     OK
aaaa                                                    OK
aaaaaa                                                  OK
aaaaaaaaaaaaaaaaa                                       OK
aaaaaaaaaaaaaaaaaaaaaaaaaa                              OK

Answer 1

Use the following printf approach to get the needed output:

#!/bin/bash
for i in a aa aaa aaaa aaaaaa aaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaa; do
    printf '%-50sOK\n' $i 
done

Script output:

a                                                 OK
aa                                                OK
aaa                                               OK
aaaa                                              OK
aaaaaa                                            OK
aaaaaaaaaaaaaaaaa                                 OK
aaaaaaaaaaaaaaaaaaaaaaaaaa                        OK

---

• OK - as static string is moved to the FORMAT (printf FORMAT [ARGUMENT])

• $i - considered as printf argument

Answer 2

An easy way:

pipe your script to column -t

$ script.sh | column -t
a                           OK
aa                          OK
aaa                         OK
aaaa                        OK
aaaaaa                      OK
aaaaaaaaaaaaaaaaa           OK
aaaaaaaaaaaaaaaaaaaaaaaaaa  OK

Answer 3

You didn't use a tool that formats output and, as $i gets wider, your output fails to align.

Replace

echo "$i $OK"

with

printf "%-50s %s\n" "$i" "$OK"

(replace "foo" by actual string).

where

• 50s is a fixed width 50 char string,
• - (minus) left-justify the string.
• see man 3 printf for details about the format string.