Shell Programming and Scripting

 "2017-09-30","ACBD,TVF","01234",NULL,18,NULL,"686091802","BANK OF ABCD, LIMITED, THE",790456

 2017-09-30|ACBD,TVF|01234|NULL|18|NULL|686091802|BANK OF ABCD, LIMITED, THE|790456

awk '{for(i=1; i<=NF; i+=2) gsub(",","|",$i)}1' FS=\" OFS= file

2017-09-30|ACBD,TVF|01234|NULL|18|NULL|686091802|BANK OF ABCD, LIMITED, THE|790456

sed '
  s/$/,/
  s/"\{0,1\}\([^"]*\)"\{0,1\},/\1|/g
  s/|$//
' file

import csv

i_file = open('input.csv', 'rb')
o_file = open('output.csv', 'wb')

reader = csv.reader(i_file)

for row in reader:
        writer = csv.writer(o_file, delimiter='|')
        writer.writerow(row)

i_file.close()
o_file.close()

csv2tsv Convert Comma-separated file to tab-separated file (tsv). (doc)
Path    : ~/executable/csv2tsv
Version : v1.1.14
Type    : ELF 64-bit LSB executable, x86-64, version 1 (GNU ...)
Home    : https://github.com/eBay/tsv-utils-dlang

"2017-09-30","ACBD,TVF","01234",NULL,18,NULL,"686091802","BANK OF ABCD, LIMITED, THE",790456

$ csv2tsv -t '|' z9

2017-09-30|ACBD,TVF|01234|NULL|18|NULL|686091802|BANK OF ABCD, LIMITED, THE|790456

OS, ker|rel, machine: Linux, 3.16.0-4-amd64, x86_64
Distribution        : Debian 8.9 (jessie) 
bash GNU bash 4.3.30

csv2tsv       Convert Comma-separated file to tab-separated file (tsv).
keep-header   Execute a command in a header aware fashion (tsv).
tsv-append    Concatenates multiple TSV files.
tsv-filter    Test fields for relationship, regular expression match, etc.
tsv-join      Match input lines against lines from a 'filter' file.
tsv-pretty    Output TSV data in a aligned format, cf. align.
tsv-sample    Randomize, sample input lines.
tsv-select    Re-order fields, cf. cut.
tsv-summarize Display results of aggregation operations on fields.
tsv-uniq      Filter out duplicate lines using fields (or line) as a key.