Is it possible to set the padding character for the printf function of gawk?

By default, gawk pads the content to the specified length with space character:

root@u2004:~# awk 'BEGIN{printf("|%+5s|n", "abc")}'
|  abc|

Is it possible to specify a custom padding character? For example, how can I get |__abc|?

Asked By: Fajela Tajkiya


No, that will not work. gawk uses the printf function which does not support other padding characters according to this reference:

Answered By: Ned64

Not directly but using GNU awk for gensub and assuming you don’t have any other blanks in your string to be printed ("abc" in this case):

$ awk 'BEGIN{ print gensub(/ /,"_","g",sprintf("|%5s|","abc")) }'

or using any awk whether your string contains blanks or not:

$ awk 'BEGIN{ base=sprintf("%1000s",""); gsub(/ /,"_",base);
        str="abc"; printf "|%s%s|n", substr(base,1,5-length(str)), str }'


$ awk '
    BEGIN{ printf "|%s|n", pad("abc",5,"_") }
    function pad(str,len,chr,    base) {
       base = sprintf("%*s",len-length(str),"")
       gsub(/ /,chr,base)
       return base str
Answered By: Ed Morton
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