KnowledgeVault — Hacker Command Reference Database

SYNOPSIS

mlr [options] {verb} [verb-options] {input-file}

FLAGS

FLAG	LONG FORM	DESCRIPTION
--csv	—	Read/write CSV format
--tsv	—	Read/write TSV format
--json	--j	Read/write JSON format
--j2c	—	JSON input, CSV output
--c2j	—	CSV input, JSON output
--nidx	—	Numerically indexed fields (like awk)
-I	—	In-place file editing
--from	—	Specify input file explicitly
--fs	--field-separator	Set field separator
--rs	--record-separator	Set record separator

EXAMPLES

#ex-01Filter rows where age > 30

mlr --csv filter '$age > 30' data.csv

OUTPUT

name,age,city
Alice,34,Boston
Marcus,41,Denver

#ex-02Sort by field name, then age descending

mlr --csv sort -f name -r age data.csv

#ex-03Rename fields

mlr --csv rename 'first_name,name,last_name,surname' data.csv

#ex-04Convert JSON to CSV

mlr --j2c cat data.json > output.csv

#ex-05Compute stats per group

mlr --csv stats1 -a mean,min,max -f salary -g department data.csv

OUTPUT

department,salary_mean,salary_min,salary_max
Eng,112000,85000,145000

#ex-06Add computed field

mlr --csv put '$bmi = $weight / ($height ** 2)' data.csv

#ex-07Chain multiple verbs

mlr --csv filter '$active == "true"' then sort -f name then cut -f name,email data.csv

SEE ALSO:awkjqcsvkitxsv

SYNOPSIS

jq [options] <filter> [file...]

FLAGS

FLAG	LONG FORM	DESCRIPTION
-r	--raw-output	Output raw strings, not JSON texts
-c	--compact-output	Compact output (no pretty-print)
-n	--null-input	Use null as input; useful for constructing JSON
-e	--exit-status	Exit 1 if last output is false or null
-s	--slurp	Read all inputs into an array
-R	--raw-input	Read each line as a string
-C	--color-output	Force colorized JSON output
-f	--from-file	Read filter from file
--arg	—	Pass a string argument to the filter
--argjson	—	Pass a JSON argument to the filter

EXAMPLES

#ex-01Pretty print JSON

cat data.json | jq '.'

OUTPUT

{
  "users": [...]
}

#ex-02Extract all user names

jq '.users[].name' data.json

OUTPUT

"Alice"
"Marcus"
"Priya"

#ex-03Filter array by condition

jq '[.[] | select(.active == true)]' data.json

#ex-04Transform keys to lowercase

jq 'with_entries(.key |= ascii_downcase)' data.json

#ex-05Merge two JSON files

jq -s '.[0] * .[1]' base.json override.json

#ex-06Count array elements

jq '.users | length' data.json

OUTPUT

#ex-07Output as CSV (raw)

jq -r '.users[] | [.name, .email, .role] | @csv' data.json

OUTPUT

"Alice","alice@corp.io","admin"

#ex-08Recursive descent — find all keys

jq '[.. | objects | keys[]] | unique' data.json

SEE ALSO:yqfxgronmlr

SYNOPSIS

grep [OPTIONS] PATTERN [FILE...]

FLAGS

FLAG	LONG FORM	DESCRIPTION
-r	--recursive	Recursively search subdirectories
-n	--line-number	Print line number with output
-i	--ignore-case	Case-insensitive matching
-v	--invert-match	Select non-matching lines
-l	--files-with-matches	Print only filenames with matches
-c	--count	Print count of matching lines per file
-A	—	Print N lines of trailing context after match
-B	—	Print N lines of leading context before match
-C	—	Print N lines of context around match
-E	--extended-regexp	Use extended regex (ERE)
-P	--perl-regexp	Use Perl-compatible regex (PCRE)
-o	--only-matching	Print only the matched part
-q	--quiet	Suppress output; exit 0 if match found
-w	--word-regexp	Match whole words only

EXAMPLES

#ex-01Basic string search

grep "error" /var/log/syslog

OUTPUT

Jun 11 04:22:18 kernel: error: device not found

#ex-02Recursive search with line numbers

grep -rn "TODO" ./src/

OUTPUT

./src/main.ts:42: // TODO: refactor this

#ex-03Invert match — exclude comment lines

grep -v "^#" /etc/ssh/sshd_config

#ex-04Case-insensitive, count per file

grep -ri -c "password" ./configs/

OUTPUT

./configs/app.conf:3
./configs/db.conf:1

#ex-05Perl regex — find IP addresses

grep -P '\b(?:\d{1,3}\.){3}\d{1,3}\b' access.log

OUTPUT

192.168.1.105 - GET /api/v2/users 200

#ex-06Context lines around match

grep -n -C 3 "CRITICAL" app.log

#ex-07Only matching text (useful with regex)

grep -oP 'user=\K[^ ]+' auth.log

OUTPUT

root
admin
deployer

#ex-08Files containing match only

grep -rl "SECRET_KEY" ./

OUTPUT

./config/secrets.py
./.env.local

#ex-09Word boundary match

grep -w "root" /etc/passwd

OUTPUT

root:x:0:0:root:/root:/bin/bash

FLAG	LONG FORM	DESCRIPTION
-F	—	Set field separator (e.g. -F: for colon)
-v	—	Assign a variable before program executes
-f	—	Read awk program from file
-i	—	In-place editing (GNU awk)
NR	—	Number of records (current line number)
NF	—	Number of fields in current record
FS	—	Field separator (default: whitespace)
OFS	—	Output field separator
RS	—	Record separator (default: newline)
ORS	—	Output record separator

FLAG	LONG FORM	DESCRIPTION
-n	--quiet	Suppress automatic printing of pattern space
-e	—	Add the script to commands to be executed
-f	—	Read script from file
-i	—	Edit files in-place (with optional backup suffix)
-r	--regexp-extended	Use extended regular expressions
s/x/y/	—	Substitute: replace x with y (first occurrence)
s/x/y/g	—	Substitute: replace all occurrences
d	—	Delete matching lines
p	—	Print matching lines (use with -n)
a\	—	Append text after matching line