How can I truncate a line of text longer than a given length?

Question

How would you go about removing everything after x number of characters? For example, cut everything after 15 characters and add ... to it.

This is an example sentence should turn into This is an exam...

Limemann

Answer 1

GnuTools head can use chars rather than lines:

head -c 15 <<<'This is an example sentence'

Although consider that head -c only deals with bytes, so this is incompatible with multi-bytes characters like UTF-8 umlaut ü.

Bash built-in string indexing works:

str='This is an example sentence'
echo "${str:0:15}"

Output:

This is an exam

And finally something that works with ksh, dash, zsh…:

printf '%.15s\n' 'This is an example sentence'

Even programmatically:

n=15
printf '%.*s\n' $n 'This is an example sentence'

If you are using Bash, you can directly assign the output of printf to a variable and save a sub-shell call with:

trim_length=15
full_string='This is an example sentence'
printf -v trimmed_string '%.*s' $trim_length "$full_string"

Tavares

cut is also an option I guess, it handles multibyte characters as well – Reportorial

${str:0:15} is very nice, thanks! – Fernandafernande

Answer 2

Use sed:

echo 'some long string value' | sed 's/\(.\{15\}\).*/\1.../'

Output:

some long strin...

---

This solution has the advantage that short strings do not get the ... tail added:

echo 'short string' | sed 's/\(.\{15\}\).*/\1.../'

Output:

short string

So it's one solution for all sized outputs.

Providential

Answer 3

Use cut:

echo "This is an example sentence" | cut -c1-15
This is an exam

This includes characters (to handle multi-byte chars) 1-15, c.f. cut(1)

     -b, --bytes=LIST
            select only these bytes

     -c, --characters=LIST
            select only these characters

Cajeput

Doesn't work well with strings containing newlines – Cleavable

Answer 4

Awk can also accomplish this:

$ echo 'some long string value' | awk '{print substr($0, 1, 15) "..."}'
some long strin...

In awk, $0 is the current line. substr($0, 1, 15) extracts characters 1 through 15 from $0. The trailing "..." appends three dots.

Gauze

Answer 5

Todd actually has a good answer however I chose to change it up a little to make the function better and remove unnecessary parts :p

trim() {
    if (( "${#1}" > "$2" )); then
      echo "${1:0:$2}$3"
    else
      echo "$1"
    fi
}

In this version the appended text on longer string are chosen by the third argument, the max length is chosen by the second argument and the text itself is chosen by the first argument.

No need for variables :)

Limemann

This is compatible with ksh, zsh, dash, and a lot more shells, as it is not a Bashism implementation: trim(){ printf '%.*s' $2 "$1";}. And if you want it Bash only but faster; you can do: printf -v trimmed_string '%.*s' $trim "$full_string" – Glindaglinka

You need examples of how to call it: trim "My Long String" <maxLen> "..." – Dereism

Answer 6

Using Bash Shell Expansions (No External Commands)

If you don't care about shell portability, you can do this entirely within Bash using a number of different shell expansions in the printf builtin. This avoids shelling out to external commands. For example:

trim () {
    local str ellipsis_utf8
    local -i maxlen

    # use explaining variables; avoid magic numbers        
    str="$*"
    maxlen="15"
    ellipsis_utf8=$'\u2026'

    # only truncate $str when longer than $maxlen
    if (( "${#str}" > "$maxlen" )); then
      printf "%s%s\n" "${str:0:$maxlen}" "${ellipsis_utf8}"
    else
      printf "%s\n" "$str"
    fi
}

trim "This is an example sentence." # This is an exam…
trim "Short sentence."              # Short sentence.

trim "-n Flag-like strings."        # Flag-like strin…
trim "With interstitial -E flag."   # With interstiti…

You can also loop through an entire file this way. Given a file containing the same sentences above (one per line), you can use the read builtin's default REPLY variable as follows:

while read; do
    trim "$REPLY"
done < example.txt

Whether or not this approach is faster or easier to read is debatable, but it's 100% Bash and executes without forks or subshells.

Manzanilla

After some discussion on the GNU mailing list, it turns out that Bash's option parsing for the echo builtin has some known POSIX-imposed limitations. Specifically, it doesn't handle the end-of-options flag as most other builtins do. Using the printf builtin is therefore the better option if the concatenated arguments to trim() could start with -n, -e, or -E. – Manzanilla