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...

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"

Answer 2

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