Padding characters in printf

Question

I am writing a bash shell script to display if a process is running or not.

So far, I got this:

printf \"%-50s %s\\n\" $PROC_NAME [UP]

Answer 1

Bash + seq to allow parameter expansion

Similar to @Dennis Williamson answer, but if seq is available, the length of the pad string need not be hardcoded. The following code allows for passing a variable to the script as a positional parameter:

COLUMNS="${COLUMNS:=80}"
padlength="${1:-$COLUMNS}"
pad=$(printf '\x2D%.0s' $(seq "$padlength") )

string2='bbbbbbb'
for string1 in a aa aaaa aaaaaaaa
do
     printf '%s' "$string1"
     printf '%*.*s' 0 $(("$padlength" - "${#string1}" - "${#string2}" )) "$pad"
     printf '%s\n' "$string2"
     string2=${string2:1}
done

The ASCII code "2D" is used instead of the character "-" to avoid the shell interpreting it as a command flag. Another option is "3D" to use "=".

In absence of any padlength passed as an argument, the code above defaults to the 80 character standard terminal width.

To take advantage of the the bash shell variable COLUMNS (i.e., the width of the current terminal), the environment variable would need to be available to the script. One way is to source all the environment variables by executing the script preceded by . ("dot" command), like this:

. /path/to/script

or (better) explicitly pass the COLUMNS variable when executing, like this:

/path/to/script $COLUMNS