1

I have this perfectly working command:

netstat -tuplean | awk '{NR>1; if( $6 ~ /ESTABLISHED/ ) print "\033[0;31m" $5 " \033[01;31m"$6;if ($6 ~ /_WAIT/ ) print "\033[0;34m"$5 " \033[01;32m"$6}'

I cannot wrap it into a watch command. Here is what I tried:

  1. escape all single quotes (')

    watch 'netstat -tuplean | awk '\''{NR>1; if( $6 ~ /ESTABLISHED/ ) print "\033[0;31m" $5 " \033[01;31m"$6 if ($6 ~ /_WAIT/ ) print "\033[0;34m"$5 " \033[01;32m"$6}'\'''

    output:

    ^[0;31m34.210.39.83:443 ^[01;31mESTABLISHED ^[0;31m34.107.221.82:80 ^[01;31mESTABLISHED ^[0;31m34.107.221.82:80 ^[01;31mESTABLISHED ^[0;34m34.117.59.81:80 ^[01;32mTIME_WAIT ^[0;34m34.117.59.81:80 ^[01;32mTIME_WAIT ^[0;31m192.168.0.1:67 ^[01;31mESTABLISHED

  2. escape both single and double quotes (' and ")

    watch 'netstat -tuplean | awk '\''{NR>1; if( $6 ~ /ESTABLISHED/ ) print '\'"\033[0;31m'\'" $5 " \033[01;31m'\'"$6 if ($6 ~ /_WAIT/ ) print '\'"\033[0;34m'\'"$5 '\'" \033[01;32m'\'"$6}'\'''

    output:

     bash: syntax error near unexpected token `print'

  3. export the command and then call it back this way:

     while : do ...<cmd>...; sleep 2;done watch -n 3 -x bash -c "$cmd"

    it does not work neither because the same problem occurs when defining the variable.

  4. I tried to make a script using while : do ...<cmd>...; sleep 2;done

    it does not work because it looks like the sleep delay is not taken into account; as a result, the output comes out too fast -- there is no way to read something.

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2 Answers 2

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4

You did not share the complete code you used in your loop-based attempts, so here are a few options you have to avoid handling multiple levels of quoting, freely based on a slightly modified AWK script.

You may save your code as an executable file:

#!/bin/bash netstat -tuplean | awk ' $6 ~ /ESTABLISHED/ { print "\033[0;31m" $5 " \033[01;31m"$6 } $6 ~ /_WAIT/ { print "\033[0;34m"$5 " \033[01;32m"$6 } $6 ~ /TIME_WAIT/ { print "\033[0;34m"$5 " \033[01;32m"$6 } END { printf("%s","\033(B\033[m") } # Turn fancy formatting off'

and make watch run it, noting that, as pointed out in the answer you already have, you also need the --color option:

watch -n 3 --color ./my_script

Alternatively, you may use an infinite loop — I am unable to guess why, in your case, "the sleep delay is not taken into account"; this seems to work as expected:

while : do clear netstat -tuplean | awk ' $6 ~ /ESTABLISHED/ { print "\033[0;31m" $5 " \033[01;31m"$6 } $6 ~ /_WAIT/ { print "\033[0;34m"$5 " \033[01;32m"$6 } $6 ~ /TIME_WAIT/ { print "\033[0;34m"$5 " \033[01;32m"$6 } END { printf("%s","\033(B\033[m") } # Turn fancy formatting off' sleep 3 done

To save your script in a variable and run it as bash -c "$cmd", you may combine command substitution and a here-document. If the label of a here-document is quoted (here, 'EOT'), its content is not expanded:

cmd=$(cat <<'EOT' netstat -tuplean | awk ' $6 ~ /ESTABLISHED/ { print "\033[0;31m" $5 " \033[01;31m"$6 } $6 ~ /_WAIT/ { print "\033[0;34m"$5 " \033[01;32m"$6 } $6 ~ /TIME_WAIT/ { print "\033[0;34m"$5 " \033[01;32m"$6 } END { printf("%s","\033(B\033[m") } # Turn fancy formatting off' EOT )
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3
  • 2
    +1. writing this as a stand-alone script is a good way to avoid quoting issues due to the conflicting quoting requirements of watch and shell and the awk script. Commented Aug 13, 2021 at 14:18
  • What is \033(B escape code for? I've asked here What is the meaning of ESC ( B ANSI escape code? Commented Oct 24, 2022 at 16:21
  • @jcubic Honestly, I wouldn't know. Most likely I took that sequence from the output of tput, using a terminal emulator where TERM was set to xterm, without much thought on the meaning of every single character. Commented Oct 24, 2022 at 18:00
3

The command where you enclosed everything in single-quotes and properly escaped the old single-quotes is almost good. It prints "garbage" because you didn't use watch --color. Run this:

watch --color 'netstat -tuplean | awk '\''{NR>1; if( $6 ~ /ESTABLISHED/ ) print "\033[0;31m" $5 " \033[01;31m"$6 if ($6 ~ /_WAIT/ ) print "\033[0;34m"$5 " \033[01;32m"$6 if ($6 ~ /TIME_WAIT/ ) print "\033[0;34m"$5 " \033[01;32m"$6}'\'

(Note the final '' in your original code is a single-quoted empty string concatenated with what's before. It changes nothing. My code omitted this useless '' completely.)

From man 1 watch:

-c, --color
Interpret ANSI color and style sequences.

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  • .@Kamil: good point to you. Regarding the final ( ' ' ), I try to keep the logic: ( ' \ ' ' ) corresponding to the end of awk snippet and one last ( ' ) corresponding to close the watch command. Commented Aug 13, 2021 at 15:17

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