How can sed output be formatted like printf's formatted printing?

Question

Can sed replace text with a string formatted like printf's formatted printing?

The following sed command replaces a line starting with the current value of "$domain" with several values specified in variables.

/bin/sed  "s/\(^${domain} *${limittype} * ${limititem}.*\)/$EXPL#\1\n${domain} ${limittype} ${limititem} ${value}/" /etc/security/limits.conf

However the output will not be properly aligned because the length of the values of domain etc. are not the same.

So the output would be something like

#oracle   hard   nproc    131072
oracle hard nproc 666

While valid, it is difficult to read. I would prefer to get something like

#oracle   hard   nproc    131072
oracle   hard   nproc    666

The best I can come with to get the desired output is:

/bin/sed  "s/\(^${domain}\)\( *\)\(${limittype}\)\( *\)\(${limititem}\)\( *\)\(.*\)/$EXPL#\1\2\3\4\5\6\7\n${domain}\2${limittype}\4${limititem}\6${value}/" /etc/security/limits.conf

But I believe there must a more elegant way to do this.

The sed one liners document contains some examples that use a specified number of characters, e.g.

sed -e :a -e 's/^.\{1,78\}$/ &/;ta'  # set at 78 plus 1 space

But this is in the regexp section not in the replacement section.

Answer 1

This uses the extended regex syntax -r, which clears up a lot of the clutter. Also, because you already know some of the field values, you don't actually need to back-reference them, again reducing clutter (and overhead).

& is a special replacement value: it hold the entire matched pattern. Using the &, again reduces clutter. As it is not a back-reference, it has significantly less overhead.

I've used ( +) vs. ( *). The + assumes that there is at least one space between input fields. Just change it to the * it that is not the case.

EXPL=
dom=oracle
typ=hard
itm=nproc
val=666

echo "oracle   hard   nproc    131072" |
  sed -r "s/^$dom( +)$typ( +)$itm( +).*/$EXPL#&\n$dom\1$typ\2$itm\3$val/" 

output

#oracle   hard   nproc    131072
oracle   hard   nproc    666

Answer 2

While you can theoretically do this entirely in sed (since it's Turing-complete), this isn't the right tool for the job.

An easy way is to insert tabs in sed, then post-process them to spaces. If you can determine the position of all columns, pipe the sed output through expand.

</etc/security/limits.conf \
sed  "s/\(^${domain} *${limittype} * ${limititem}.*\)/$EXPL#\1\n${domain}\t${limittype}\t${limititem}\t${value}/" |
expand -t 10,17,26

(Use a literal tab character instead of \t if your sed doesn't support \t.)

If you don't know the column widths in advance, try the BSD column utility. It looks at the whole input file to determine column widths that accommodate the length of all rows.

</etc/security/limits.conf \
sed  "s/\(^${domain} *${limittype} * ${limititem}.*\)/$EXPL#\1 ${domain} ${limittype} ${limititem} ${value}/" |
column -t

If your sed script rewrites both commented-out lines and non-commented-out lines, or if you use column, you'll need a bit of post-processing to skew the commented-out lines by the width of the comment marker.

… | sed '/^#/ s/ //'

You can use awk instead. It has a printf function. As an added bonus, there is an easy way to protect special characters such as . or * in a searched-for column content.

</etc/security/limits.conf awk -v domain="$domain" -v limittype="$limittype" -v limititem="$limititem" -v value="$value" '
$1 == domain && $2 == limittype && $3 == limititem  {
    printf "#%-9s %-8s %-9s %s\n%-9s %-8s %-9s %s\n", $1, $2, $3, $4, $1, $2, $3, value; next
}
1 {print}
'

Answer 3

Just use printf to format sed output:

printf "%5s %12s %4s\n" $(sed 's/.../.../')