How to write a shell script to swap columns in txt file? - bash

Question

I was trying to solve one of my old assignment I am literally stuck in this one Can anyone help me?
There is a file called "datafile". This file has names of some friends and their
ages. But unfortunately, the names are not in the correct format. They should be
lastname, firstname
But, by mistake they are firstname,lastname
The task of the problem is writing a shell script called fix_datafile
to correct the problem, and sort the names alphabetically. The corrected filename
is called datafile.fix .
Please make sure the original structure of the file should be kept untouched.
The following is the sample of datafile.fix file:
#personal information
#******** Name ********* ***** age *****
Alexanderovich,Franklin 47
Amber,Christine 54
Applesum,Franky 33
Attaboal,Arman 18
Balad,George 38
Balad,Sam 19
Balsamic,Shery 22
Bojack,Steven 33
Chantell,Alex 60
Doyle,Jefry 45
Farland,Pamela 40
Handerman,jimmy 23
Kashman,Jenifer 25
Kasting,Ellen 33
Lorux,Allen 29
Mathis,Johny 26
Maxter,Jefry 31
Newton,Gerisha 40
Osama,Franklin 33
Osana,Gabriel 61
Oxnard,George 20
Palomar,Frank 24
Plomer,Susan 29
Poolank,John 31
Rochester,Benjami 40
Stanock,Verona 38
Tenesik,Gabriel 29
Whelsh,Elsa 21

Answer 1

If you can use awk (I suppose you can), than this there's a script which does what you need:
#!/bin/bash
RESULT_FILE_NAME="datafile.new"
cat datafile.fix | head -4 > datafile.new
cat datafile.fix | tail -n +5 | awk -F"[, ]" '{if(!$2){print()}else{print($2","$1, $3)}}' >> datafile.new
Passing -F"[, ]" allows awk to split columns both by , and space and all that remains is just print columns in a needed format. The downsides are that we should use if statement to preserve empty lines and file header also should be treated separately.
Another option is using sed:
cat datafile.fix | sed -E 's/([a-zA-Z]+),([a-zA-Z]+) ([0-9]+)/\2,\1 \3/g' > datafile.new
The downside is that it requires regex that is not as obvious as awk syntax.

Answer 2

awk -F[,\ ] '
!/^$/ && !/^#/ {
first=$1;
last=$2;
map[first][last]=$0
}
END {
PROCINFO["sorted_in"]="#ind_str_asc";
for (i in map) {
for (j in map[i])
{
print map[i][j]
}
}
}' namesfile > datafile.fix
One liner:
awk -F[,\ ] '!/^$/ && !/^#/ { first=$1;last=$2;map[first][last]=$0 } END { PROCINFO["sorted_in"]="#ind_str_asc";for (i in map) { for (j in map[i]) { print map[i][j] } } }' namesfile > datafile.fix
A solution completely in gawk.
Set the field separator to both , and space. Then ignore any lines that are empty or start with #. Mark the first and last variables based on the delimited fields and then create a two dimensional array called map indexed by first and last name and the value equal to the line. At the end, set the sort to indices string ascending and loop through the array printing the names in order as requested.

Answer 3

Completely in bash:
re="^[[:space:]]*([^#]([[:space:]]|[[:alpha:]])+),(([[:space:]]|[[:alpha:]])*[[:alpha:]]) *([[:digit:]]+)"
while read line
do
if [[ ${line} =~ $re ]]
then
echo ${BASH_REMATCH[3]},${BASH_REMATCH[1]} ${BASH_REMATCH[5]}
else
echo "${line}"
fi
done < names.txt
The core of this is to capture, using bash regex matching (=~ operator of the [[ command), parenthesis groupings, and the BASH_REMATCH array, the name before the comma (([^#]([[:space:]]|[[:alpha:]])+)), the name after the comma ((([[:space:]]|[[:alpha:]])*[[:alpha:]])), and the age ( *([[:digit:]]+)). The first-name regex is constructed so as to exclude comments, and the last-name regex is constructed as to handle multiple spaces before the age without including them in the name. Preconditions: Commented lines with or without leading spaces (^[[:space:]]*([^#]), or lines without a comma, are passed through unchanged. Either first names or last names may have internal spaces. Once the last name and first name are isolated, it is easy to print them in reverse order followed by the age (echo ${BASH_REMATCH[3]},${BASH_REMATCH[1]} ${BASH_REMATCH[5]}). Note that the letter/space groupings are counted as matches which is why we skip 2 and 4.

Answer 4

I have tried using awk and sed.
Try if this works
less dataflie.fix | sed 's/ /,/g' | awk -F "," '{print $2,$1,$3}' | sed 's/ /,/' | sed 's/^,//' | sort -u > dataflie_new.fix