I have a txt file in a format like this:

test1
test2
test3

How can I bring it into a format like this using bash?

test1,test2,test3

CodePudding user response：

Assuming that “using Bash” means “without any external processes”:

if IFS= read -r line; then
  printf '%s' "$line"
  while IFS= read -r line; do
    printf ',%s' "$line"
  done
  echo
fi

CodePudding user response：

Old answer here

TL;DR:

cat "export.txt" | paste -sd ","

CodePudding user response：

Another pure bash implementation that avoids explicit loops:

#!/usr/bin/env bash

file2csv() {
    local -a lines
    readarray -t lines <"$1"
    local IFS=,
    printf "%s\n" "${lines[*]}"
}

file2csv input.txt

CodePudding user response：

You can use awk. If the file name is test.txt then

awk '{print $1}' ORS=',' test.txt | awk '{print substr($1, 1, length($1)-1)}'

The first awk commad joins the three lines with comma (test1,test2,test3,). The second awk command just deletes the last comma from the string.

CodePudding user response：

Use tool 'tr' (translate) and sed to remove last comma:

tr '\n' , < "$source_file" | sed 's/,$//'

If you want to save the output into a variable:

var="$( tr '\n' , < "$source_file" | sed 's/,$//' )"

CodePudding user response：

Using sed:

$ sed ':a;N;$!ba;s/\n/,/g' file

Output:

test1,test2,test3

I think this is where I originally picked it up.

CodePudding user response：

If you don't want a terminating newline:

$ awk '{printf "%s%s", sep, $0; sep=","}' file
test1,test2,test3

or if you do:

awk '{printf "%s%s", sep, $0; sep=","} END{print ""}' file
test1,test2,test3

CodePudding user response：

Another loopless pure Bash solution:

contents=$(< input.txt)
printf '%s\n' "${contents//$'\n'/,}"

• contents=$(< input.txt) is equivalent to contents=$(cat input.txt). It puts the contents of the input.txt file (with trailing newlines automatically removed) into the variable contents.
• "${contents//$'\n'/,}" replaces all occurrences of the newline character ($'\n') in contents with the comma character. See Parameter expansion [Bash Hackers Wiki].
• See the accepted, and excellent, answer to Why is printf better than echo? for an explanation of why printf '%s\n' is used instead of echo.