Find ending position of whitespace in a Bash script

Question

I am writing a Bash script and I would like to find the end position of the whitespace in multiple strings. I can't just search for spaces, because it might have tabs in it. Below are a few examples of lines I might search.

11:tcp_listen         1.2.3.4:3478
12:tcp_listen              [::1]:3478
13:tcp_listen               [2600:2700:2800:2900:3000:3100:3200:3300]:3478

• First Line: Whitespace Ending Position: 21
• Second Line: Whitespace Ending Position: 26
• Third Line: Whitespace Ending Position: 24

I am looping through each line, and have each line as a variable.

Example:

line="11:tcp_listen         1.2.3.4:3478"

Answer 1

Attempting to paste mixed spaces and tabs fails in this web page, but:

$ line="11:tcp_listen         1.2.3.4:3478"
$ shopt -s extglob                                  # important!
$ prefix_with_spaces=${line%%+([^[:space:]])}
$ echo ">$prefix_with_spaces<"
>11:tcp_listen         <
$ echo ${#prefix_with_spaces}
22

Let's try it with actual tabs

$ line=$'11:tcp_listen\t\t1.2.3.4:3478'
$ prefix_with_spaces=${line%%+([^[:space:]])}
$ echo ${#prefix_with_spaces}
15

I'm using shell parameter expansion and extended patterns. Check the man page for details.

Similarly, if you want to get the text following the last space: same technique, simpler pattern:

$ line="11:tcp_listen         1.2.3.4:3478"
$ suffix=${line##*[[:space:]]}
$ echo ">$suffix<"
>1.2.3.4:3478<
$ line=$'11:tcp_listen\t\t1.2.3.4:3478'
$ suffix=${line##*[[:space:]]}
$ echo ">$suffix<"
>1.2.3.4:3478<