How to use printf to print a character multiple times? - awk

Question

Using printf, one can print a character multiple times:
$ printf "%0.s-" {1..5}
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In awk I know that I can do something like:
$ awk 'BEGIN {while (i++ < 5) printf "-"}'
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But I wonder if awk's printf allows this as well.
I went through the printf modifiers page but could not find how. All in all, what the printf from Bash does is to expand {1..5} and print a - for every parameter it gets, so it is equivalent to saying
$ printf "%0.s-" hello how are you 42
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However, I lack the knowledge on how to mimic this behaviour with awk's printf, if it is possible, because this fails:
$ awk 'BEGIN {printf "%0.s-", 1 2 3 4 5}'
-

Answer 1

I do not believe this is possible with awk's printf, as there is also no way to do this just with printf in C and C++.
With awk, I think the most reasonable option is using a loop like you have. If for some reason performance is vital and awk is creating a bottleneck, the following will speed things up:
awk 'BEGIN {s=sprintf("%5s","");gsub(/ /,"-",s);print s}'
This command will run logarithmically faster[1] Though, it won't cause a noticeable difference in performance unless you're planning on printing a character many times. (Printing a character 1,000,000 times will be about 13x faster.)
Also, if you want a one-liner and are using gawk, even though it's the slowest of the bunch:
gawk 'BEGIN {print gensub(/ /,"-","g",sprintf("%5s",""));}'
[1] While the sprintf/gsub command should always be faster than using a loop, I'm not sure if all versions of awk will behave the same as mine. I also do not understand why the while-loop awk command would have a time complexity of O(n*log(n)), but it does on my system.

Answer 2

I know this is old but the width modifier can be used e.g.
l = some_value
print gensub(/ /, "-", "g", sprintf("%*s", l, ""))
will print a variable number of - depending on the value of l
This was GNU Awk 3.1.8

Answer 3

If you can assume a (modest) upper bound on how long the result should be, how about something like this:
l = 5;
print substr("---------------------", 1, l);
Besides being dead simple, this has the benefit that it works in versions of AWK that lack the "gensub()" function.

Answer 4

i know this post is old, but thought it would be worth demonstrating functionality to allow dynamic control of character string length using basic awk.
A simple example incorporating a string of length 'var' into a printf statement
$ echo "1 foo baa\n2 baa foo" | awk -v var=6 'BEGIN{for(i=1;i<=var;i++) l=l "-" }{printf "%s" l "%s" l "%s\n",$1,$2,$3}'
1------foo------baa
2------baa------foo
You can either split the format string and insert your character string as I've done above. Or you can give the string it's own format specifier
$ echo "1 foo baa\n2 baa foo" | awk -v var=6 'BEGIN{for(i=1;i<=var;i++) l=l "-" }{printf "%s%s%s%s%s\n",$1,l,$2,l,$3}'
both output the same.
A more complicated example that column justifies text. (I've actually used basic 'print' rather than 'printf' in this case, although you could use the latter, as above).
$ echo "Hi, I know this\npost is old, but thought it would be worth demonsrating\nfunctionality to allow a dynamic control of\ncharacter string lengths using basic awk." |
awk '{
line[NR]=$0 ;
w_length[NR]=length($0)-gsub(" "," ",$0) ;
max=max>length($0)?max:length($0) ;
w_count[NR]=NF
}END{
for(i=1;i<=NR;i++)
{
string="" ;
for (j=1;j<=int((max-w_length[i])/(w_count[i]-1));j++)
string=string "-" ;
gsub(" ",string,line[i]) ;
print line[i]
}
}'
Hi,--------------I--------------know--------------this
post-is-old,-but-thought-it-would-be-worth-demonsrating
functionality---to---allow---a---dynamic---control---of
character---string---lengths---using---basic---awk.