How to read value from a file in shell scripting? - shell

Question

I am trying to get read value from a file in shell script based on input. How I can do it ?
I tried in different way but not able to read value in below file.
# dates
dates:
start: '10-09-2018'
end: '10-02-2019'
# filters
filters:
- table: 'employee'
column: 'sex'
operation: '=='
value: M
- table: 'employee'
column: 'department'
operation: 'notin'
value: ['operation', 'sales']
- table: 'organisation'
column: 'org_id'
operation: '=='
value: 124
- table: 'organisation'
column: 'org_name'
operation: '=='
value: XYZ LIMITED
My expected output,
If I pass 'filters' and table name 'employee' as input, I should get output as sex='M' and department <> 'operation' and department <> 'sales'
Can anyone help me on this.

Answer 1

So, assuming you fix the indentation in that example so it's valid YAML, the following perl script produces what you want:
#!/usr/bin/perl
use warnings;
use strict;
use YAML::XS qw/LoadFile/;
my ($file, $mapping, $table) = #ARGV;
my $yaml = LoadFile $file;
die "No such mapping: $mapping\n" unless exists $yaml->{$mapping};
my %ops = ('==' => '=', 'notin' => '<>');
my $first = 1;
for my $elem (#{$yaml->{$mapping}}) {
if ($elem->{'table'} eq $table) {
my $col = $elem->{'column'};
my $value = $elem->{'value'};
my $op = $elem->{'operation'};
$op = $ops{$op} // $op;
print ' and ' unless $first;
$first = 0;
if (ref $value eq 'ARRAY') {
print join(" and ", map { "$col $op '$_'" } #$value);
} else {
print "$col $op '$value'";
}
}
}
print "\n";
Example:
$ perl boringname.pl example.yaml filters employee
sex = 'M' and department <> 'operation' and department <> 'sales'
Requires the YAML::XS module, installable through your favorite CPAN client or your OS package manager (Ubuntu calls the package libyaml-libyaml-perl. Not sure about others.).