Remove special characters from 2nd column of a file - linux

Question

I have a file s.csv
a,b+ -.,c
aa,bb ().,c._c
I want to remove all special characters from 2nd column (file separated by comma)
cat s.csv | tr -dc '[:alnum:]\n\r' | tr '[:upper:]' '[:lower:]'
The above code also removes special characters from 3rd column as well.
awk -F, '{print $2}' s.csv | tr -dc '[:alnum:]\n\r' | tr '[:upper:]' '[:lower:]'
This code only print 2nd column.
Any idea how can I remove special char from 2nd column and price all
Required output should be
a,b,c
aa,bb,c._c

Answer 1

Remove all (from second field)
characters that are not upper case letters [^A-Z
or lower case letters a-z
or digits 0-9]
from second field $2
fields are with "," separated -F ','
keep the separator in output OFS=FS
$ awk -F ',' 'BEGIN{OFS=FS}{gsub(/[^A-Za-z0-9]/,"",$2); print}' s.csv
# test
$ awk -F ',' 'BEGIN{OFS=FS}{gsub(/[^A-Za-z0-9]/,"",$2); print}' <<<'aa,bb ().,c._c'
aa,bb,c._c
As #Léa Gris mentioned below
Don't forget to set the locale to C or [^A-Za-z0-9] is gonna be
interpreted unexpectedly in non-western European alphabets. Prepend
awk invocation with
LC_ALL=C

Answer 2

You can use the [:alpha:] character class using awk, here for second field and remove with gsub() function the characteres that aren't alpha:
awk 'BEGIN{OFS=FS=","} {gsub(/[^[:alpha:]]+/, "", $2)} 1' file
a,b,c
aa,bb,c._c
if you need other set of characters, you can see this answer of Ed Morton:
https://stackoverflow.com/questions/56481541/how-can-you-tell-which-characters-are-in-which-character-classes
and see "which characters are in which character classes"

Answer 3

Use this Perl one-liner:
perl -F',' -lane '$F[1] =~ s{[\W_]+}{}g; #F = map { lc } #F; print join ",", #F; ' in_file > out_file
The Perl one-liner uses these command line flags:
-e : Tells Perl to look for code in-line, instead of in a file.
-n : Loop over the input one line at a time, assigning it to $_ by default.
-l : Strip the input line separator ("\n" on *NIX by default) before executing the code in-line, and append it when printing.
-a : Split $_ into array #F on whitespace or on the regex specified in -F option.
-F',' : Split into #F on comma, rather than on whitespace.
s{[\W_]+}{} : Replace 1 or more occurrences of \W (non-word character) or underscore with nothing.
The regex uses these modifiers:
/g : Match the pattern repeatedly.
SEE ALSO:
perldoc perlrun: how to execute the Perl interpreter: command line switches
perldoc perlre: Perl regular expressions (regexes)
perldoc perlre: Perl regular expressions (regexes): Quantifiers; Character Classes and other Special Escapes; Assertions; Capture groups
perldoc perlrequick: Perl regular expressions quick start

Answer 4

You don't have to alter locale just to do it - by using octals instead of letters, the regex engine respects them as ASCII instead of being overly clever - i even intentionally set it to Belgian French to illustrate :
CODE
echo 'a,b+ -.,c
aa,bb ().,c._c' | {m,g}awk '
gsub("[^\\060-\\071\\101-\\132\\141-\\172]+","",$(!_+!_))^_' \
OFS=',' FS=','
OUTPUT
a,b,c
aa,bb,c._c
SHOWCASE LOCALE=C isn't needed
LANG="fr_BE.UTF8" gawk -e '
BEGIN { for(_=8*4;_<8^4;_++) { printf("%c",_) } } ' |
LANG="fr_BE.UTF8" gawk -p- -e '
gsub("[^\\060-\\071\\101-\\132\\141-\\172]+","",$-_)^_' OFS=',' FS=','
——————————
0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz
# profile gawk, cr'e'e Sun May 29 05:58:26 2022
# R`egle(s)
1 (gsub("[^\\060-\\071\\101-\\132\\141-\\172]+", "", $-_)) ^ _ { # 1
1 print
}