Shell Programming and Scripting

Code:

n=10 ; echo "ABCD" | sed 's/^/'$(printf "%${n}s" "")'/'

Hello dae,

Could you please try following too.

Code:

echo "abcd" | awk '{while(i<10){Q=Q? Q OFS:OFS;i++};print Q $0}'

Output will be as follows.

Code:

          abcd

Thanks,
R. Singh

Rdrtx1's proposal is exactly what I was looking for ... but I am absolutely unable to understand it !

if one of you has an idea ?

Thanks again,

This...

Code:

sed 's/^/          /g'

and that...

Code:

n=10
sed 's/^/'$(printf "%${n}s")'/'

are basically the same. The only difference is that the second one creates the 10 spaces in a (bash) subshell. The command printf "%10s" creates exactly 10 spaces. I omitted the arg "". Syntactically not correct, but it works too.

Thanks stomp for explanation. Just wanted to add a bit here. It creates 10 spaces in subshell by (printf) and substituted the starting of line by doing sed 's/^/' with those 10 spaces.

Thanks,
R. Singh

When I try the command:

Code:

n=10 ; echo "ABCD" | sed 's/^/'$(printf "%${n}s" "")'/'

on OS X El Capitan Version 10.11.6 using ksh version 93u+ 2012-08-01 and with bash version 3.2.57(1)-release (x86_64-apple-darwin15) I get a syntax error similar to:

Code:

sed: 1: "s/^/": unterminated substitute in regular expression

which I believe is what is required by the standards since the output of the command substitution is not quoted.

And, while it is true that some shells will manufacture an empty string argument or a zero numeric argument to match printf format specifiers, that behavior is not required by the standards and will result in syntax errors in some shells with a built-in printf utility and in some stand-alone implementations of the printf utility.

Either of the following should work with any standards conforming shell, sed, and printf utilities:

Code:

n=10 ; echo "ABCD" | sed 's/^/'"$(printf "%${n}s" "")"'/'

or:

Code:

n=10 ; echo "ABCD" | sed 's/^/'"$(printf '%$*s' "$n" "")"'/'

or, if the string you want to print is in a variable instead of being read from standard input:

Code:

n=10; string="ABCD"; printf "%$ns%s" "" "$string"

or:

Code:

n=10; string="ABCD"; printf '%*s%s' "$n" "" "$string"

In all of these cases, as already explained, the commands:

Code:

printf '%Ns" "string"
printf '%*s" N "string"

where N is a non-negative integer will print the string specified by the last operand right justified in a field that is N characters wide with leading space fill. If the string specified by the last operand is more than N characters, it will not be truncated. If you wanted a field of exactly 6 characters no matter how long the given string is, you can specify both a minimum and a maximum field width. And, you can also specify left justified text instead of right justified text. The following code:

Code:

printf 'X%6.6sX\n' "ABCD"
printf 'X%-6.6sX\n' "ABCD"
printf 'X%6.6sX\n' "abcdefgh"

producing the output:

Code:

X  ABCDX
XABCD  X
XabcdefX

What a "big jump" in my knowledge thanks to all your contributions ... Don, I got the same error for myself but I decided to do not bother all of you more with my problem !

Thanks again for your help and the time spent !