Shorten lines, adding "..." ellipsis

Question

How to cut off lines that are longer than some width, and marking the lines that were chopped off with an ellipsis?

Only lines that were actually shortened should be marked, but not lines that had just the right lenght in the first place.

I would like to use the command in a pipeline.

Answer 1

This will truncate the string, chop off an additional three characters, and add "..." if the length is longer than the value you supply as a parameter.

other_programs | \
awk -v len=40 '{ if (length($0) > len) print substr($0, 1, len-3) "..."; else print; }'

Answer 2

Try this:

awk -F '' '{if (NF > 70) {print substr($0, 0, 71)"..."} else print $0}'

If NF is too high, the simpler way:

awk '{if (length($0) > 70) {print substr($0, 0, 71)"..."} else print $0}'

or a shorter version:

awk 'length > 70{$0=substr($0,0,71)"..."}1'

Answer 3

Some possibilities:

• with sed

  sed -E 's/(.{N})(.{1,})$/\1.../' file
  

• slightly more elegantly with perl (using lookbehind)

  perl -pe 's/(?<=.{N}).{1,}$/.../' file
  

where N is the number of characters after which you wish to replace with the ellipsis.

Answer 4

awk, sed, and perl, as presented in the other answers, excel at text processing and are probably the best tools for the job.

But you can also do this in pure bash (i.e., "without leaving the shell"), if you like:

n=70
while read -r; do
    if ((${#REPLY}<=n))
        then printf '%s\n' "$REPLY"
        else printf '%s...\n' "${REPLY:0:$((n-3))}"
    fi
done < filename

Replace 70 with the maximum desired length, and filename with the input file.

To use this on the right side of a pipe (i.e., to pipe another command's output to it), remove < filename and either set n beforehand or enclose the whole thing in { ... ;}:

{ n=70
while read -r; do
    if ((${#REPLY}<=n))
        then printf '%s\n' "$REPLY"
        else printf '%s...\n' "${REPLY:0:$((n-3))}"
    fi
done ;}

(This bracket-enclosed version also works fine in other contexts, including with redirection as above. The brackets are unnecessary in that use case, but not harmful.)

This looks like:

ek@Ilex:~$ help read | head -5 | { n=70
> while read -r; do
>     if ((${#REPLY}<=n))
>         then printf '%s\n' "$REPLY"
>         else printf '%s...\n' "${REPLY:0:$((n-3))}"
>     fi
> done ;}
read: read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N n...
    Read a line from the standard input and split it into fields.

    Reads a single line from the standard input, or from file descr...
    if the -u option is supplied.  The line is split into fields as...

Note that, in common with the other solutions that have been presented so far, this will fail to perfectly limit output width in the presence of characters that display more than one column wide, such as horizontal tabs.

Answer 5

Another perl solution:

perl -ple '$_ = sprintf "%.70s...", $_ if length > 70' file

Answer 6

The accepted answer written as a function with example, also putting the ... in the middle of the string rather than the end:

truncate_string() { 
    echo "$@" | \
    awk -v len=15 '{ if (length($0) > len) print substr($0, 1, len-3) "..." substr($0, length($0) - len, length($0)); else print; }'
}

example:

parse_branch() {
    branch=$(git symbolic-ref --short HEAD || hg branch)
    truncate_string "$branch"
}

NB I do not recall but since it was long ago but I might have used this on Mac? Or was it linux (vagrant??)