use awk variable in bash script

Question

I have a txt file with blow format:

66.57.21 - john
88.43.23 - albert
10.10.11 - smith

I wanna to execute "connect.py 66.57.21 john" for each line and I wrote this bash script:

#!/bin/bash
while read LINE; do
awk -v number = "$LINE" '$1'
awk -v name = "$LINE" '$3'
  connect.py $name $number
done < "$1"

but the bash script didn't work

What is the problem

Why not while read -r ip stuff user; do connect.py "$ip" john; done < file.txt? By reading into 3 variables, the read will separate the information for you. — David C. Rankin
– David C. Rankin, Commented Nov 10, 2021 at 23:35
See BashFAQ #1: How can I read a file (data stream, variable) line-by-line (and/or field-by-field)? And that use of awk is pretty completely wrong. — Gordon Davisson
– Gordon Davisson, Commented Nov 10, 2021 at 23:41

Ed Morton · Accepted Answer · 2021-11-11 17:21:51Z

1

#!/usr/bin/env bash
while read -r number _ name; do
  connect.py "$name" "$number"
done < "$1"

edited Nov 11, 2021 at 17:21

answered Nov 11, 2021 at 17:16

Ed Morton

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1 Comment

hek2mgl Over a year ago

Hey! connect.py "$name" "$number" < /dev/tty might be safer in case connect.py would read from stdin.

Robby Parker · Accepted Answer · 2021-11-12 05:49:21Z

0

If you are wanting to use awk, here is one way to do it:

awk -F" " '{system("connect.py " $3 " " $1)}' input.txt

The -F" " splits each line of input on spaces

$1 is the first word in the array (number in the original question)

$3 is he third word in the array (name in the original question)

wrapping "connect.py " $3 " " $1 in system() causes the shell to execute the command after the substitutions have been made

ie: connect.py john 66.57.21

edited Nov 12, 2021 at 5:49

answered Nov 10, 2021 at 23:55

Robby Parker

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4 Comments

David C. Rankin Over a year ago

One thing you want to avoid in scripting is spawning subshells within a loop. That makes shell scripts S L O W.... Here you are spawning 9 subshells every iteration. Command substitution spawns a subshell. Each pipe takes a subshell and you have commands on either side of the pipe. Ouch! If you are reading 1000 or so lines, no problem, if it is 1,000,000 - go get lunch and check back much later. Always try and limit or eliminate this type behavior. Here, if you want to use awk, you can do the entire thing in a single call to awk and use system() for the connection. Advice -- no dings.

David C. Rankin Over a year ago

Also, you are commiting a UUOc (Unnecessary Use of cat, also stated as Useless Use of cat). Whenever you do cat file ... and are not concatenating files, it is a UUOc. Usually seen as cat file | someUtility. See Useless Use of Cat. Instead all utilities will either take the filenames as an argument or take input on stdin. So it is properly someUtility file or someUtility < file. ... :)

Ed Morton Over a year ago

You also have unquoted variables, are using read in a way it'll corrupt lines containing escapes, using all upper case variable names inappropriately, etc. Copy/paste your script into shellcheck.net and it'll tell you about some of the issues.

Robby Parker Over a year ago

Thank you both. I have updated based on your collective feedback. Let me know what you think.

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