I think you're looking for expand and/or unexpand. It seems you're trying to ensure a \tab width counts as 8 chars rather than the single one. fold will do that as well, but it will wrap its input to the next line rather than truncating it. I think you want:
expand < input | cut -c -80
expand and unexpand are both POSIX specified:
- The
expand utility shall write files or the standard input to the standard output with \tab characters replaced with one or more space characters needed to pad to the next tab stop. Any backspace characters shall be copied to the output and cause the column position count for tab stop calculations to be decremented; the column position count shall not be decremented below zero.
Pretty simple. So, here's a look at what this does:
unset c i; set --;
until [ "$((i+=1))" -gt 10 ]; do set -- "$@" "$i" "$i"; done
for c in 'tr \\t \ ' expand; do eval '
{ printf "%*s\t" "$@"; echo; } |
tee /dev/fd/2 |'"$c"'| {
tee /dev/fd/3 | wc -c >&2; } 3>&1 |
tee /dev/fd/2 | cut -c -80'
done
The until loop at top gets a set of data like...
1 1 2 2 3 3 ...
It printfs this with the %*s arg padding flag so for each of those in the set printf will pad with as many spaces as are in the number of the argument. To each one it appends a \tab character.
All of the tees are used to show the effects of each filter as it is applied.
And the effects are these:
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
66
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8
105
Those rows are lined up in two sets like...
- output of
printf ...; echo
- output of
tr ... or expand
- output of
cut
- output of
wc
The top four rows are the results of the tr filter - in which each \tab is converted to a single space.
And the bottom four the results of the expand chain.
Best Answer
It is easiest with
awkwhich treats multiple consecutive spaces as a single one, soprints
But obviously there are many, many other tools which will do the job, even not designed to such task as
grep: