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https://github.com/adrianlarion/text-processing-recipes-linux

Text processing recipes & reference on Linux.
https://github.com/adrianlarion/text-processing-recipes-linux

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Text processing recipes & reference on Linux.

Host: GitHub
URL: https://github.com/adrianlarion/text-processing-recipes-linux
Owner: adrianlarion
Created: 2021-11-16T13:19:26.000Z (almost 3 years ago)
Default Branch: master
Last Pushed: 2021-11-24T20:23:11.000Z (almost 3 years ago)
Last Synced: 2024-05-19T00:39:17.012Z (6 months ago)
Size: 36.1 KB
Stars: 56
Watchers: 2
Forks: 9
Open Issues: 1
Metadata Files:
- Readme: README.md

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README

# Text Processing Recipes Linux.
Linux text processing reference & recipes.
Featuring: `vim, tr, cat, tac, sort, shuf, seq, pr, paste, fmt, cut, nl, split, csplit, sed, awk, grep` and regex.

# TABLE OF CONTENTS
* [Basic Regex](#basic-regex)
* [General Tools & Recipes](#general-tools)
* [grep](#grep)
* [sed](#sed)
* [awk](#awk)
* [vim-tips](#vim)

# Recommended books (not written by me)
[Definitive Guide to sed - by Daniel Goldman](https://amzn.to/3cnzQCS)

[Sed & Awk - Dale Dougherty & Arnold Robbins](https://amzn.to/3kKck7Y)

[Effective awk programming - by Arnold Robbins](https://amzn.to/30scfhM)

# Basic Regex.

#### Literal. Matches 'hello'
`hello`

#### Any single character.
`.`

#### Two any single characters
`..`

#### Multiple specific characters. 'a' or 'b' or 'c'
`[abc]`

#### Character range. All characters between a-z.
`[a-z]`

#### Multiple ranges.All between a-z and A-Z.
`[a-zA-Z]`

#### Ranges + extra characters. Chars from 1-9 and 'a','b','c'
`[1-9abc]`

#### Negated chars. Any char that is NOT 'a', 'b', or 'c'
`[^abc]`

#### Negated char ranges. Any char NOT between a-z.
`[^a-z]`

#### * multiplier. Any char zero or more times. Works on the preceding ITEM.
`.*`

#### * multiplier again. Char 'a', followed by char 'b' (preceding item) zero or more times. This is how all multipliers work.
`ab*`

#### ? multiplier. Any char zero or one times.
`.?`

#### + multiplier. Any char one or more times.
`.+`

#### Numbered multiplier. Character 'l' five times. ('lllll')
`l{5}`

#### Numbered range multiplier. Char 'a' between 1-5 times ('a', 'aa','aaa', etc)
`a{1-5}`

#### Open ended numbered range multiplier. Char 'a' at least 2 times.
`a{2,}`

#### Greedy matching (default). From 'hello you loving kool kaizer king' will match 'llo you loving kool kaizer k'
`l.*k`

#### Lazy matching. From 'hello you loving kool kaizer king' will match 'llo you loving k' and 'l k'. In most cases this is the desired behaviour.
`l.*?k`

#### Shorthand char classes:
```
\s - whitespace (space, newline, tab, etc)
\S - oposito of \s (not whitespace)
\d - digit (0-9)
\D - not digit
\w - word char ([a-zA-Z0-9_])
\W - not word char
```

#### ^ beginning of line. Beginning of line followed by 'h', 'e','l','l' and 'o'
`^hello`

#### $ end of line. 'b','y','e' followed by end of line.
`bye$`

#### \b - beginning or end of word. Will match ' FOO' at end of line but not 'BARFOO' at end of line.
`\bFOO$`

#### Group in parenthesis. Back reference it by '\1'. 'foo' is group 1. Matches 'foo bar foo' (foo, followed by bar followed by first group which is 'foo')
`(foo) bar \1`

#### Alternation. 'foo' or 'bar'
`foo|bar`

# General Tools

#### Replace ':' with tabs in the output
`cat /etc/passwd | tr ':' '\t'`

#### Delete unwanted chars ('#')
`echo "hello # world" | tr -d '#'`

#### replace all but the alphanumeric chars with `_`
`cat main.py | tr -c '[:alnum:]\n' '_'
```
___usr_bin_python3
from_termcolor_import_colored__cprint
import_sys
for_i_in_range_0_10__
____print_str_i__end___r__
```

#### Convert all to uppercase:
`cat main.py | tr 'a-z' 'A-Z'`

#### Convert all to lowercase:
`cat main.py | tr 'A-Z' 'a-z'`

#### Swap uppercase/lowercase
```
tr 'a-zA-Z' 'A-Za-z'
```
1 4 7
2 5 8
3 6 9
```

#### Gen numbers, put them on 3 cols, separated by commas:
`seq 9 | pr -3ts, `

```
1,4,7
2,5,8
3,6,9
```

#### Gen numbers, put them on 3 cols ACROSS (from left to right, not top to bottom), separated by commas, :
`seq 9 | pr -3ats, `
```
1,2,3
4,5,6
7,8,9
```

#### Put the contents of files each on a column, separated by tabs. Works well with files with short lines.
`pr -mts file1 file2`
```
10 100
100 One thousand
20 2000
25 2,5
one one and tow
extra
extra2
extra3
```

#### Generate rand nums from: 1-10, 1-100. Put them on columns separated by tabs.
`pr -mts <(shuf -n10 -i 1-10) <(shuf -n10 -i 1-100)`

```

2 62
10 88
4 76
6 96
5 35
1 39
7 64
3 1
9 48
8 53
```

#### Generate 100 sequential numbers. Put them on 5 columns separated by tabs ('t' stands for no header (no extra whitespace at the bottom usually)
`seq 100 | pr -5t`

```

1 21 41 61 81
2 22 42 62 82
3 23 43 63 83
4 24 44 64 84
5 25 45 65 85
6 26 46 66 86
7 27 47 67 87
8 28 48 68 88
9 29 49 69 89
10 30 50 70 90
11 31 51 71 91
12 32 52 72 92
13 33 53 73 93
14 34 54 74 94
15 35 55 75 95
16 36 56 76 96
17 37 57 77 97
18 38 58 78 98
19 39 59 79 99
20 40 60 80 100
```

#### Another way to put contents of a file on columns (across), separated by tabs. One column for one dash (3 cols total)
```
paste - - - > for each record (line) in all the files passed to awk
>>> if record (line) matches `/bilbo/` pattern
>>>> print the whole record (line)

#### Field
* How about `/bilbo/ {print $1}`? `$1` represents the first field (word) from the current record (line). `$2` is second field (word) and so on.
* You can read `/bilbo/ {print $1}` as:
>> for each record (line) in all the files passed to awk
>>> if record (line) matches `/bilbo/` pattern
>>>> print the first field (word) from the record (line)

#### Pattern AND Pattern
* Patterns can be more complex. Check this out `/bilbo/&&/frodo/{print "my precious"}`
* You can read this as:
>> On each record (line) that matches `/bilbo/` AND `/frodo/`
>>> print the string "my precious"

#### Pattern OR Pattern
* Check this other pattern out `/bilbo/||/frodo/{print "Is it you mister Frodo?"}`
* You can read this as:
>> On each record (line) that matches `/bilbo/` OR `/frodo/`
>>> print the string "Is it you mister Frodo?"

#### NOT Pattern
* What about `! /frodo/ { print "Pohtatoes" }`? (note the extra spaces put there for clarity. You could also eliminate them to save typing)
* Read it as:
>> On each record (line) that DOESN'T match `/frodo/`
>>> Print "Pohtatoes"

#### IF Pattern present then check for Pattern, ELSE check for Pattern
* Here's a more complex example `/frodo/ ? /ring/ : /orcs/{ print "Either frodo with the ring, or the orcs" }`
* `a?b:c` is a ternary operator. It reads: if a then do b, else do c.
* Read it as:
>> Read record.
>>> If it matches `/frodo/`
>>>> Does it also match `/ring/`? If yes then print "Either frodo with the ring, or the orcs"
>>> If it doesn't match `/frodo/`
>>>> Does it match `/orcs/`? If yes then print "Either frodo with the ring, or the orcs"
* The actions are executed if: a record (line) contains either ("frodo" and the "ring") OR (no "frodo" and "ring") but "orcs".

#### Pattern Range
* How about this one? `/Shire/ , /Osgiliath/ { print $0 }`?
* The comma separated regex expressions are a "pattern range".
* Read this as:
>> Execute command for each record (line)
>>> Between the record (line) that matches `/Shire/` (including that record (line))
>>> And record (line) that matches `/Osgiliath/` (including that record(line))
* If you have a file that looks like:
```
What is it mister Frodo?
Do you miss the Shire?
I miss the shire too.
This Osgiliath is to drab for me.
Too many orcs.
```
* The above command will simply print the records(lines):
```
Do you miss the Shire?
I miss the shire too.
This Osgiliath is to drab for me.
```

#### BEGIN Pattern
* You'll be interested in this one. `BEGIN {print "And so it begins"}`
* BEGIN is a special pattern, triggered right at the beginning, before any input from files is read.
* NOTE - BEGIN will execute it's command even if no files are passed
* It reads:
>> Before any input is read
>>> Print "And so it beggins"

#### END Pattern
* If something begins, it has to end, right? `END {print "There and back, by Bilbo Baggins"}`
* END is triggered when awk has finished reading input from all files. Thus it needs files passed to awk in ordered to be triggered
* It reads:
>> After all input was read
>>> Print "There and back, by Bilbo Baggins"

#### BEGINFILE, ENDFILE Patterns
* If you pass multiple files to awk - it will treat them as being one contiguous file. But what if you want to call some commands when beginning to read input from a file? You use BEGINFILE and ENDFILE respectively.
* `BEGINFILE {print "A new chapter is beginning mister Frodo"}`
* It reads:
>> Before input is read from a file
>>> print "A new chapter is beginning mister Frodo"

#### NO Pattern
* This a simple one. `{print $1}`.
* When no pattern is provided, just the command in curly braces, it is executed for all records (lines).
* This reads
>> For all records (lines):
>>> print the first word

#### Conditional Pattern
* `NF>4{print}`
* The pattern is `NF>4`. If true then exec commands inside curly braces.
* NF is the Number of Fields(words). If the current record (line) has more than 4 fields (words), print the record (line)

#### About commands
* All commands MUST be inside curly braces. You can't just call `print $0`. You have to put that command inside curly braces - `{print $0}`

#### Variables
* Awk has some built in variables. They are written in uppercase.
* They can be useful in a variety of cases.
* `FILENAME` is the name of the current file being processed.
* `BEGINFILE {print "we are beginning to process " FILENAME}` will print the string followed by the name of the file when awk begin processing file.
* `NR` is the Record Number (or Number Record if you'd like). In simple terms it's the record (line) count. If awk is processing line number 5 then NR is 5.
* Let's say you have a 10 line file and a 5 line file. You pass both files to awk. Awk finishes the first 10 lines and is now at line 3 from the second file. How much will the NR be?
* You might be tempted to say 3 - but it's 13. NR stands for ALL the records (lines) that awk processes, not records (lines) belonging to file.
* If you want to refer to record (line) count for file you would use FNR. F - from File. File Number Record.
* In the case above NR would be 13 but FNR would be 3.

#### More Variables
* Here's a list of the most important variables with a short description
* `FILENAME` - name of file
* `FNR` - File Number Record (input record number for current file - according to official docs). File record (line) count.
* `FS` - Field separator (word separator if you'd like). Space by default.
* `IGNORECASE` - if set to 1 case is ignored. Very important. `/frodo/` would match `Have you seen my old ring Frodo?` if IGNORECASE is 1. If set to 0 it would not. Use it like this:
```
BEGIN {IGNORECASE=1}
/frodo/ {print "do you remember the taste of strawberries Frodo?"}
```
* `NF` - number of fields (words) in the current record (line). You could use this to count words for example.
* `NR` - Number Record. Global record (line) count if you will.
* `RS` - Record Separator. A newline by default.

#### Programming intro
* Awk is a full blown programming language. It has all the operators & syntax you would expect from a "regular" programming language such as C or python.
* This is taken directly from the manual
```
Operators
The operators in AWK, in order of decreasing precedence, are:

(...) Grouping

$ Field reference.

++ -- Increment and decrement, both prefix and postfix.

^ Exponentiation (** may also be used, and **= for the assignment operator).

+ - ! Unary plus, unary minus, and logical negation.

* / % Multiplication, division, and modulus.

+ - Addition and subtraction.

space String concatenation.

| |& Piped I/O for getline, print, and printf.

< > <= >= == !=
The regular relational operators.

~ !~ Regular expression match, negated match. NOTE: Do not use a constant regular expression (/foo/) on the left-hand side of a ~ or !~. Only use one on the right-hand side. The expression
/foo/ ~ exp has the same meaning as (($0 ~ /foo/) ~ exp). This is usually not what you want.

&& Logical AND.

|| Logical OR.

?: The C conditional expression. This has the form expr1 ? expr2 : expr3. If expr1 is true, the value of the expression is expr2, otherwise it is expr3. Only one of expr2 and expr3 is
evaluated.

= += -= *= /= %= ^=
Assignment. Both absolute assignment (var = value) and operator-assignment (the other forms) are supported.

Control Statements
The control statements are as follows:

if (condition) statement [ else statement ]
while (condition) statement
do statement while (condition)
for (expr1; expr2; expr3) statement
for (var in array) statement
break
continue
delete array[index]
delete array
exit [ expression ]
{ statements }
switch (expression) {
case value|regex : statement
...
[ default: statement ]
}

```

#### Programming usage
* Here's how you could use the "programming" part of awk:
```
#!/usr/bin/awk -f
BEGIN {
IGNORECASE=1
hobitses=0
}
/fellowship/ {
if (index($0,"samwise") >0 ) {
hobitses+=1
print "Hurry up hobitses"
}
}
END {
print "Found a total of " hobitses " hobitses"
}
```

* Let's break this down.
* You see that this is an awk script because of the shebang (the line beginning with `#!/...`)
* Before reading any input set the built in var IGNORECASE to 1. "frodo" will match "Frodo", "FRODO", "frodo", etc.
* We also set a custom variable for our own usage and set its initial value to 0 (hobitses)
* Check all records (lines) and on those that match `/fellowship/` execute the following:
>> Check if we have the string "samwise" inside the record (line). Index is a built in function. It takes two strings. If the second string is contained within the first it will return a value bigger than 0. If the second string is not present in the first return 0.
>> If index() returns a value bigger than 0 ("samwise" was found inside the current record (line)) do the following:
>>> increase hobitses by 1
>>> print a message
* After processing all the records print a message with value of our custom variable "hobitses".

#### Options
* You can pass options to awk. Here are some useful ones:
* `-f` read awk source file. `awk -f source.awk file.txt`. You put all awk code in the source.awk file. NOTE - don't put the shebang (`#!/usr/bin/awk -f`)
* `-F` - field separator. Use to define "words". For example if you have a .csv you could make the separator a comma. Like this: `awk -F, '{print $2} file.txt ' - will print the second "word" separated by comma.
* `-v` assign a variable. Eg: `awk -v count=0 '/bilbo/{count+=1;print "Found another one. Now count is " count}' f1`. init count to 0. On records matching `/bilbo/` increment count by 1. Print the message.
* `-e` - execute commands. Use multiple awk commands. Eg: `awk -e 'BEGIN {IGNORECASE=1}' -e '/bilbo/{"Found him"}'`

#### String concatenation
* `print "hello" "world"` will output "helloworld". No space between.
* `print "hello","world"` will output "hello world". A space between by using a comma in print.

#### System commands
* You can execute system commands like so `awk '{system("ls "$1" -la")}' file.txt `.
* Let's break it down. We start by calling the system function on every record (line). We pass an argument built dynamically. "ls " followed by the first field (word) followed by " -l". If the field was "myfile.txt" the command would be "ls myfile.txt -la"
* note the spaces at the end in "ls ". If you don't put the space the command would look like "lsmyfile.txt -la" which won't work obviously.
* It will output something like:
```
-rw-rw-r-- 1 me me 0 Nov 14 17:40 f1
-rw-rw-r-- 1 me me 59 Nov 14 17:41 f2
-rw-rw-r-- 1 me me 20 Nov 12 15:42 col1
```
* Basically we run `ls` on the first word of every file passed to awk.

#### Writing dynamically to files
* If you find a certain pattern you might like to write that to a file (with some extra info maybe).
* `awk '/Bilbo/{print "I found him. First word is " $1 >> "appended.txt"}' file.txt `. It will append the print message (followed by first field(word)) to the file appended.txt
* Use '>' instead of '>' to overwrite the file (instead of appending)

#### System commands with stdin
* You can pipe with print into certain system commands. Here's an example `awk '{print "file.txt" | "xargs -n1 ls -l"}'`
* "file.txt" is piped into the command "xargs -n1 ls -l". Similar to `echo "file.txt" | xargs -n ls -l`
* The advantage is that you can pass "dynamic" arguments. Certain fields (words) for example.
* The output looks like:
```
-rw-rw-r-- 1 me me 0 Nov 14 17:40 file.txt
```

#### Getline example
* `"date" | getline cur_date` - run "date", store into variable cur_date. This a simple use for getline.
* Here's a cooler one `awk '{"du "$0" |cut -f1" |getline cur_size;print "for file " $0 " size is " cur_size}' filenames.txt`
* Let's break it down. "du "$0" |cut -f" will look like "du myfile.txt | cut -f1". This linux command will output the size of the file in kb.
* We pass this value to the variable "cur_size".
* We use a semicolon to separate commands. Next we print the value of the variable "cur_size"

#### $ - the positional variable
* $ is not a "normal" variable but rather a function triggered by the dolar sign (according to grymoire awk tut)
* `X=; print $X;` means `print $1`.
* You can do more fancy stuff with this. `'{print $(NF-1)}' - NF is the number of fields (words) in the record (line). `$NF` would be the last field (word) (if there are 5 fields NF is 5. $NF will point to the 5th field (word))

#### Modify the positional variable
* You can modify a certain field (word) and print the record (line) containing that modified field.
* `echo "Meat's back on the menu" | awk '{$5="NO_MENUS_IN_ORC_LAND";print}'` will output `Meat's back on the NO_MENUS_IN_ORC_LAND`
* We assign a value to field number 5. Then we print the record (print with no arguments prints the current record, just like `$print $0`)

#### Selective .csv column print
* You have a .csv in the form:
```
city,area,population
LA,400,100
Miami,500,101,
Buenos Aires,800,102
```
* As you can see you have 3 columns. You would like to print the 1st and 3rd column only.
* This should do the trick `awk -F, '{print $1,$3}' cities.csv`
* We set a custom field (word) separator with `-F,`.
* Note the comma between the positional arguments. IF you remember `{print "a" "b"}` will output "ab". You need comma to separate by space, `{print "a","b"}`.
* You can get fancy and skip the header row of the csv with `awk -F, '{if (NR>1) print $1,$3}' cities.csv `. If Number Record is bigger than 1 (not the first) only then print.

#### Custom field separator with OFS
* `{print "a", "b"}` will output "a b". When a comma is present awk uses the output field separator (OFS) which is a space by default.
* You can change OFS to something else, like `::` for example. `{OFS="::";print "a", "b"}` will output `a::b`

#### Mix with command line text
* Let's say you have a file produced by the `ls` command, like this:
```
drwxr-xr-x 2 root root 69632 Nov 13 19:21 .
drwxr-xr-x 16 root root 4096 Nov 9 07:35 ..
-rwxr-xr-x 1 root root 59888 Dec 5 2020 [
-rwxr-xr-x 1 root root 18456 Feb 7 2021 411toppm
-rwxr-xr-x 1 root root 39 Aug 15 2020 7z
-rwxr-xr-x 1 root root 40 Aug 15 2020 7za
-rwxr-xr-x 1 root root 40 Aug 15 2020 7zr
-rwxr-xr-x 1 root root 35344 Jul 1 00:42 aa-enabled
-rwxr-xr-x 1 root root 35344 Jul 1 00:42 aa-exec
```
* you want to print the name of the executable but only if it's smaller than 50 bytes. Use this `awk '{if ($5<50) print $9}' bin_10 `
* If the fifth field (containing size in bytes) is smaller than 50 print the 9th field (name of executable)

#### Math on text.
* This is one of the cool things about awk. You can take some text, perform all kinds of programming magic on it, spit it out nice and modified. Usually you need to write a lot of boilerplate if you're using a general scripting language like python.
* Let's take the cities .csv again:
```
city,area,population
LA,400,100
Miami,500,101,
Buenos Aires,800,102
```
* Check out this script.
```
#!/usr/bin/awk -f
BEGIN {
total=0
FS=","
}
{
if (FNR>1) {
real_pop=$3 * 1000
total+=real_pop
print "Real population of", $1, "is" ,real_pop
}
}

END {

print "Total Population:", total
}
```

* The output will be:
```
Real population of LA is 100000
Real population of Miami is 101000
Real population of Buenos Aires is 102000
Total Population: 303000
```
* By now you should understand what this does. We start by creating a variable and setting it to 0. We set the Field separator to a comma because we have a csv.
* If the File Number Record is bigger than 1 do stuff (note how we use FNR, not NR. That's because we want to skip the header of every file, not just the first file).
* We do some math, addition/multiplication. Finally we print the total. This works with multiple csv files.
* With a bit of care we could cram it on 1/2 lines in the terminal.

#### Fancy line numbers
* Look at this beaut: `awk '{print "(" NR ")" ,$0}' f1`
* It will print the line number in parenthesis followed by the actual line (from a file that doesn't have line numbering). Something like :
```
(1) line one
(2) line two
```
* Carefully study the spaces and commas from print. We know that by not using a command strings will be concatenated without any separator in between. So `"(" NR ")"` will output something like `(9)`. We could even dispense with the spaces in the command (`"("NR")"`) but I've kept them because they make things clearer. Next we print the actual line. Note the comma. It means awk will put a space (OFS) between the parenthesised line number and the actual line.

#### Print words by their number
* It's time to get fancy and change Field Separator and Record separator.
* By default RS is a newline. What happens if you change it into an empty string?
* Vim will load all the file in memory and treat it as a single record.
* FS (Field Separator)remains the same. But since the whole file it's treated as a single record the positional variable will refer to word number in FILE (not in record/line).
* Sounds complicated? It's not. You have a file like this:
```
first second third
fourth fifth sixth
seventh eight
```
* This is the awk script.
```
#!/usr/bin/awk -f
BEGIN { RS="" }
{
print $1, $8
}
```
* It will output `first eight`.
* Look at the script again. If RS would be a newline `print $1, $8` would print something like:
```
first
fourth
seventh
```
* It prints the first field on each record but since records are lines it can't find the eight field (word).
* But when the whole file is treated as a single record the positional variable ($) refers to field number in whole file.
* You can put this on a one liner and use it daily: `awk 'BEGIN{RS=""}{print $1020}' file.txt `

#### Pass stdin to awk (and show nicely formatted size of files)
* `ls -lh | awk '{print $9,"has size of",$5}'`
* Generate text with `ls -lh` that looks something like:
```
-rwxr-xr-x 1 root root 39 Aug 15 2020 7z
-rwxr-xr-x 1 root root 40 Aug 15 2020 7za
-rwxr-xr-x 1 root root 40 Aug 15 2020 7zr
```
* pipe it to awk. Print field $9 (filename) and field $5 (size)

#### Pass both stdin and file to awk
* `echo "Coming from stdin" | awk "{print}" file.txt -`
* In the above command awk first processes file.txt then stdin (passed by using the final dash)

#### Check if text coming from stdin or file
* `{ if (FILENAME!="-") print $0 }` it's the script.
* When you pass it both stdin and files `echo "Coming from stdin" | awk "{print}" file.txt -` awk won't process text from stdin.

#### Arrays intro
* `{myarr=["one","two","three"]}` - WON'T work, even though this is the syntax used by many languages to declare arrays
* Use instead something like `{myarr[0]="one";myarr[1]="two"}`
* Arrays are associative. You associate an index with a value. Like a dictionary.
```
#!/usr/bin/awk -f
{
myarr["hobits"]="hobitses"
print(myarr["hobits"])
}
```
* As you can see you can use strings and numbers as an index (as a key). In the end though array subscripts are always strings.
* That is `{print myarr[5.1]}` will check for an '5.1' string index.

#### Store lines in array
```
#!/usr/bin/awk -f
/bilbo/ {
myarr[NR]=$0
}
END{
for (i in myarr){
print "subscript is",i
print myarr[i]
}
}
```
* For each record (line) that matches `/bilbo/` store the record(line) in 'myarr', using the current NR (Number Record - or current line count) as a subscript/index

* At the end enumerate over indexes in my arr (NOT over elements) with a 'for..in' loop.
* It will print something like:
```
subscript is 3
a story by frodo and bilbo
subscript is 13
bilbo again and frodo
```
* Note how this array is not contiguous. It is sparse. The indexes between 0-3 and 3-13 don't exist and are not assigned automatically. Kinda make sense since awk uses strings and NOT integers as indexes/subscripts.

#### Delete array elems
* `{delete myarr[1]}` will delete element at index '1' (where '1' is a string).
* `{delete myarr}` - will delete ALL elements of the array

#### Array index concatenation
```
#!/usr/bin/awk -f
BEGIN{
arr[1,2]="one"
arr["abc","bcd"]="two"
arr["abc",1]="three"
arr["foo" "bar"]="four"
arr["bar" "foo"]="five"
for (i in arr){
print "at index",i,"value is",arr[i]
}
}
```
* Will output:
```
at index abc1 value is three
at index abcbcd value is two
at index foobar value is four
at index barfoo value is five
at index 12 value is one
```
* Awk treats integers as strings when used as array indexes. Then it concatenates them if you pass multiple values, either separated by space, comma or not separated at all. There is no space between these concatenated values.

* Another thing to note is that the 'for..in' loop doesn't enumerate elems in the order they were added.

#### Ordered array indexes
```
#!/usr/bin/awk -f
BEGIN{
i=0
arr[""]=0
}
/bilbo/{
arr[i++]=$0
}
END{
for (j=0;j4) next; print}' file.txt`
* If NF (Number of Fields) is bigger than 4 stop processing current input record and get the "next" one. Else print the record.
* This will in effect print lines that have 4 or less fields (words)

#### Some math funcs
```
{
print "log",log($1),$2
print "col",cos($1),$2
print "sin",sin($1),$2
print "rand",rand()
}
```
* Pretty self explanatory math funcs. rand() will print a rand float between 0 and 1.

#### Print some random integers (1000 rand ints between 0-100)
```
#!/usr/bin/awk -f
BEGIN {
for (i=0; i<1000; i++) printf("%d\n",rand()*100)
}
```
* We create random ints between 1 and 100 by multiplying the rand float (between 0-1) with 100 and cutting off the digits by using a `%d` (decimal) in printf, which treats any numbers as ints (an cuts the digits)

#### String funcs - index
```
#!/usr/bin/awk -f
{
i=index($0,"bilbo")
print $0
if (i>0) print ">>>> INDEX IS",i
}
```
* the 'index()' func searches for the index of the second string ("bilbo") in the first string (the current record/line). If none found it returns 0.

#### String funcs - length
* very basic but very much needed functionality - the length of a string.
* `awk '{print "[",$0,"]","has length of",length($0)}' file.txt` outputs something like:
```
[ Hello world world ] has length of 17
[ hello andback again Again ] has length of 25
[ a story by frodo and bilbo with ring ] has length of 36
```

#### String funcs - split
* Split a string into parts based on a separator (regex or string).
```
#!/usr/bin/awk -f
BEGIN {
mystring="The best | leaf in the Shire, isn't it?"
n=split(mystring,array," ")
for (i in array) print array[i]
print "TOTAL splits:",n
}
```
* will output:
```
The
best
leaf
in
the
Shire,
isn't
it?
TOTAL splits: 8
```
* First parameter is the string. The second parameter is an array in which to store the split parts of the string. We can pass an uninitialized variable directly. The last param is the separator.
* The function returns the number of splits (in the 'n') variable. It returns the split string components in the array "array" passed as argument.

#### String funcs - substr
```
#!/usr/bin/awk -f
BEGIN {
mystring="lotr is cool"
n=substr(mystring,1,3)
print n
}

```
* will output:
`lot`
* substring returns a portion of the string. First arg is the string. Second is the index from where to start cutting. The indexing begins from 1, NOT 0. So first char is at index 1. The final (optional) arg is the length of the cut.
* Read it as: get 3 chars from the first char (including the first char).
* If you don't pass the third arg (length) it will cut until the end of string.
* Use it in a one-liner to print the first X chars of every line ` awk '{print substr($0,1,10)}' file.txt`

#### String funcs - gensub
```
#!/usr/bin/awk -f
BEGIN {
mystring="Run Halifax. Show us the meaning of haste."
res=gensub(/[Hh]ali/,"Shadow","g",mystring)
print res
}
```
* will output:
` Run Shadowfax. Show us the meaning of haste.`
* first arg is the regex to search for. Second is the replacement string. Third is a flag. It can be "g" for global or an integer. If it's "g" it replaces all occurrences of regex in mystring. If it's for example 2 it will replace only the second occurrence of regex. The last arg is the target string (where to do search & replace)
* gensub will return a new string, leaving the original intact.
* If you look at it you'll notice that it's similar to sed's substitute: `s/[Hh]ali/Shadow/g`
* If the last (target) string not supplied, use $0 (the current record)

#### String func - gsub
* gsub is similar to gensub but has some diffs. It doesn't take the flag argument and replaces globally by default. It also performs search & replace directly on the target string. It returns the number of substitutions (whereas gensub() returns the modified string)
* This make it very useful for modifying records nicely and rapidly.
* `awk '{gsub(/bilbo/,"MASTER BILBO");print}' file.txt` will search for `/bilbo/` on the current record (line) and replace it with "MASTER BILBO".

#### String func - sub
* Just like gsub() but only replaces the FIRST occurrence.
* `awk '{sub(/bilbo/,"MASTER BILBO");print}' file.txt` will search for `/bilbo/` on the current record (line) and replace it with "MASTER BILBO", just the FIRST occurrence on the record

#### String func - match
* Returns 0 if a match is not found, otherwise the starting index for the match (index STARTING AT 1, not 0)
* Look at this:
```
#!/usr/bin/awk -f
{
i=match($0,/bilbo/)
if (i>0){
res=substr($0,i,5)
print res
}
}

```
* It returns the index for `/bilbo/` in current record. If bigger than 0 then get a substring (from 'i' to 'i'+5)

#### String func - tolower
* `echo "My Precious!" | awk '{print tolower($0)}'`
* Will output `my precious!`

#### String func - toupper
* `echo "My Precious!" | awk '{print toupper($0)}'`
* Will output `MY PRECIOUS!`

#### String func - asort
* Sorting an array of numbers or string might come in hand.
```
#!/usr/bin/awk -f
BEGIN {
for (i=0;i<5;i++){
arr[i]=rand()*100
print arr[i]
}
print ">> SORTED"
asort(arr)
for (i in arr)print arr[i]
}

```
* will output:
```
92.4046
59.3909
30.6394
57.8941
74.0133
>> SORTED
30.6394
57.8941
59.3909
74.0133
92.4046
```

#### Time func - strftime
* ` awk 'BEGIN {print strftime("%a %b %e %H:%M:%S %Z %Y")}' will output `Sun Nov 14 15:09:56 EET 2021`
* Here's the format specifiers (taken from grymoire.com). (The man has some format specifiers but it's not this complete)
```
%a The locale's abbreviated weekday name
%A The locale's full weekday name
%b The locale's abbreviated month name
%B The locale's full month name
%c The locale's "appropriate" date and time representation
%d The day of the month as a decimal number (01--31)
%H The hour (24-hour clock) as a decimal number (00--23)
%I The hour (12-hour clock) as a decimal number (01--12)
%j The day of the year as a decimal number (001--366)
%m The month as a decimal number (01--12)
%M The minute as a decimal number (00--59)
%p The locale's equivalent of the AM/PM
%S The second as a decimal number (00--61).
%U The week number of the year (Sunday is first day of week)
%w The weekday as a decimal number (0--6). Sunday is day 0
%W The week number of the year (Monday is first day of week)
%x The locale's "appropriate" date representation
%X The locale's "appropriate" time representation
%y The year without century as a decimal number (00--99)
%Y The year with century as a decimal number
%Z The time zone name or abbreviation
%% A literal %.
```

#### Extract the inverse of a regex match
* When you use match() func and get an actual match you'll modify RSTART and RLENGTH. These are 2 built in awk vars that signify the start and the length of the match.
* You can use these vars to extract the inverse of a regex match. This might come handy in certain advanced scenarios.
```
#!/usr/bin/awk -f
{
reg="[Bb]ilbo"
if (match($0,reg)){
bef=substr($0,1,RSTART-1)
aft=substr($0,RSTART+RLENGTH)
pat=substr($0,RSTART,RLENGTH)
print bef,"|",pat,"|",aft
}
else print $0
}

```
* This will output something like:
```
Hello world world
hello andback again Again
a story by frodo and | bilbo | with ring with bilbo
| Bilbo | baggins baggins baggins
```
* We start by checking for a match. If a match exists commands inside if will run (since it will return a value greater than 0).
* 'bef' is the substring before the match. We cut it from position beginning (string indexing starts at 1) up to the start of the match (to RSTART).
* 'aft' is the substring after the match. We cut it from the end of the match up to the end. Note how we use "RSTART+RLENGTH" to calculate the first char AFTER the end of the match. This it's a bit confusing with indexing starting from 1. If you're used to 0 indexing you would want to add a 1 ("RSTART+RLENGTH+1") but it's not needed here because indexing starts at 1.
* Note the comments starting with `#`

#### Put all lines on one line
* Check out this wacky oneliner `awk '{a=a $0}END{print a}' file.txt`
* It will concatenate all lines on a single line (without any separators between lines).
* Here's how it works. We start by declaring a variable a. Simply using it will make it uninitialized the first time awk encounters the variable name. Uninitialized variables have a value of "". You can use whatever var name you like, I used "a" because it's short and simple.
* On every record (line) add to "a" previous value of "a" + the current record (line). Awk concatenates values simply by putting them one after another. The line above would even work even without any spaces - eg `{a=a$0}` but I kept the space for clarity.
* After all input records are done processing print the final value of "a". "a" now contains all lines concatenated together.
* Feel free to add some separators between lines for clarity, like: `awk '{a=a"|"$0}END{print a}' file.txt`

#### User declared funcs
```

#!/usr/bin/awk -f

# Declare custom func outside
function throw_ring(who){
if (who=="gollum"){
return 0
}
else if (who=="frodo"){
return 1
}
}

# On all records matching /ring/
/ring/{
# Find gollum or frodo
if (match($0,"gollum")){
was_thrown=throw_ring("gollum")
#use ternary if/else. If was_thrown is true (or bigger than 0) return "THROWN". Else return "NOT THROWN"
print "the ring throw status is ", was_thrown?"THROWN":"NOT THROWN"
}

if (match($0,"frodo")){
was_thrown=throw_ring("frodo")
print "the ring throw status is ", was_thrown?"THROWN":"NOT THROWN"
}

}

```
* This is a rather lange script but simple when you break it into pieces.
* Start by declaring a custom "throw_ring" function.
* on records that match `/ring/` exec the following operations:
* check if that record (which contains `/ring/`) contains "gollum". If yes get "thrown_status" value.
* Use the ternary operator to return either "THROWN" or "NOT_THROWN".
* Do the same for "frodo"
* The output will look like: `the ring throw status is THROWN`

#### More about conditional patterns
* Conditional patterns are powerful and succint. We can use them to check for certain conditions before executing any commands inside curly braces.
* `NF>4{print}` is equivalent to `{if(NF>4)print}`. As you can see the first one is clearer and shorter. It uses a conditional pattern. If true, exec commands inside curly braces.
* The second runs for every record and inside curly braces use a conditional 'if'.
* We can use fairly advanced conditional patterns, using parenthesis and &&, || and even functions.
* `awk 'match($0,/bilbo/){print}` - if we find `/bilbo/` inside current record print. Obviously we could've dispensed with the match and simply used a regular pattern.
* But the power comes from combination with other tests. `awk '(NF>6)&& match($0,/bilbo/) {print}' file.txt`. If Number of Fields is bigger than 6 AND we have `/bilbo/` inside current record, print.
* We can replace match with the match operator - `~`. Like this: `NF>6 && $0~/bilbo {print}`. If Number of Fields bigger than 6 and we have a match of `/bilbo/` inside current record, print.

#### Advanced conditional patterns
* Here's a mind blowing one: `awk 'NF==3,/bilbo/{print}' f1`. The comma signifies a range (as for pattern range). But we use a conditional pattern as the start of the range and a regex as the end of the range. Pretty powerful stuff.
* The line above will print before the first record where Number of Fields is 3 and up to (and including) the last record containing `/bilbo/`
* Here's a simpler but highly useful oneliner `awk 'NF!=0{print} file.txt`. If Number of Fields different than 0, print. It will skip printing empty lines.
* This one will make you oogle. `awk 'rand()>0.5{print}' file.txt`. It will print about half lines from 'file.txt', depending on the result of 'rand()'.

#### Print the first Nth lines of every file
* `awk 'FNR<=5{print}' f1 f2 f3`
* The line above will print the first 5 lines of every file passed to awk (without any separation between them). It uses a conditional pattern. If File Number Record smaller or equal to 5, print.

#### Print until you encounter this pattern. Then move to next file.
* `awk '{if ($0~/bilbo/) nextfile;print}' f1 f2`.
* Print records (lines) from current file until you encounter `/bilbo/` in current record (line). Then move to the next file (skipping the rest of the current file).
* Do the same for the rest of the files.
* It will NOT print the line containing `/bilbo/`.

#### Print every Nth line of file
* `awk '{getline;print}' file.txt` - print every second line of the file.
* Why? For every record start with `getline`. This command sets '$0' from the next input record - it basically reads the next line into '$0'. Print then prints the newly updated '$0'
* `awk '{getline;getline;print}' file.txt` - print every third line of the file. We consume two lines then print the third one. And so on. Add more `getline` to increase `Nth` printing.

# Vim

### HOW TO READ SHORTCUTS:

`` - Escape. Usually you should press the key, not type it. When you see `ii` you type ii and then Escape, not 'ii` literally.

`` - means Ctrl+G

`g` - means press g then press Ctrl+g

`` - means press SHift+g

`` - means Ctrl+Shift+Z (Shift is not shown but implied since we have an uppercase Z)

`` - z followed by Shift+Z

`` - type Ctrl+M followed by Enter. `` is Carriage Return (another word for Enter key)

### Find files and send them to vim.
```find ~ -size +10M | vim -```

* find files and open the results in vim. While in vim you can press `gf` to open a file (from the results provided by find) in vim.
- HINT: if your file has spaces vim will complain that the file is not in the path. This happens because it truncates the file when a space appears, thus trying to reach the file at an erroneous path. So instead use `` to select the hole line and then press `gf`
- HINT2 - you can use any other command that outputs to stdout and send it to vim.
- HINT3 - you can open the file under cursor in a new window with `f`

### Encrypt
* You decide to write your secret journal using vim. Trouble is - anyone can read your unencrypted text files. Or can they? By using `vim -x mysecretfile.txt` you use encryption on file. You'll be asked for a key (password) to encrypt/decrypt your file. Warning - if you forget your key bye bye file.
- HINT - you can also encrypt a file after you open it by typing `:X`

### Macros
* I'm still amazed by how many vim users totally ignore the power of register playback. That is - you record your actions into a register and play those actions back. It's a bit weird to wrap your head around it but once you do - you'll be amazed.
Here's how it works
- press `qa` to start recording your actions into register `a`
- Perform some actions that you want repeated. Here's a very useful example for coders - custom line by line editing. Let's say that you need to go line by line, search for the word "foo" and place it in tags () and place those tags again on the same line at the end of the line.
- This is a pretty complex scenario. Doing it by hand for thousands of lines it's PITA (Pain In The A*s). What can you do? Write an awk script? A Python script? NOOOOO. You use vim register playback.
- So you start your action by implementing a movement that will go to the next line or the next pattern. This is very important because it will make the playback "smart", as it will go on the next line or pattern and do the work.
- In your case you would start by typing `/foo` and pressing `` (Enter). This takes care of always finding the next pattern and working on it.
- No do your desired operations. `i<ea>` which will insert the bracket, then to normal mode, go te end of the word, append the closing bracket.
- next you copy the whole bracketed foo by pressing `ya>` (yank all in between brackets) followed by `$p` (go to end of the line and paste)
- Your work is done. You press `q` to stop recording.
- time for PAYBACK ...ah, I meant PLAYBACK.
- you press `@a` to playback the contents of register `a` (into which you recorded your actions). You watch amazed how vim repeats "smartly" the operations you just performed previously.
- Now you can press `@@` to repeat the previous playback as many times as you want. Or you could press `10@@` to repeat the playback for 10 times. Or if you want this applied to your whole file type `:% norm @a` - which means - apply the macro to all lines.

### Open files in own tab/win
* Your girlfriend's father comes to visit you. You want to impress him by opening a bunch of text files, each in it's own window in vim (and show him that you're very smart and tech savvy)
- You write `vim -o f1 f2 f3 f4` to open the specified files with windows split horizontally. use `vim -O f1 f2 f3` to split them vertically. If you have lots of files and you dont want a hundred narrow windows use `vim -o5 *.txt` to open a max of 5 windows (horizontally stacked).
- You could instead open them in tabs by using the same syntax `vim -p f1 f2` or `vim -p5 *.txt`

### Info
* The `` magic - it displays file name and position. `g` will display number of words, num of lines and other useful stats.

### Enter special chars
* Enter digraphs (speciar chars). Use `` in Insert mode and type the digraph code. For example you can enter the pound sign using 'Pd' (£). Type `:h digraph-table` for more info. To just view the codes type `:dig`

### Quickly write buffer to disk
* `ZZ` - write the buffer to disk if modified and exit. I bet you didn't knew that - but if you did BRAVO, you know how to quit Vim!

### Sort
* `:%!sort -u` - sort all lines and remove duplicates. `%` refers to the range and it means all the lines. You could use `1,5` for example and it would only sort lines 1 to 5. The `!` in this context means - execute an external shell command (in our case sort) with the range as stdin, when you're done put back in place the stdout from that command.

### Paste register
* While in insert mode press `` followed by a registry, such as `a` or `b` or `@` or `:` or `+`. eg: `a`. This will insert the contents of the registry at cursor.

### Insert mode navig
* While in insert mode press `` to backspace a char, `` to delete a word backwards, `` to delete until the beginning of the line (all without leaving Insert mode)

### Autocomplete
* Did you knew you also have autocomplete by default? While in insert mode press `` or `` to cycle through possible autocompletions.

### How to quit Vim
* There are lots of famous memes about people not knowing how to quit Vim. Here's a little secret - you can quit the current buffer(if you opened just a single file) without writting to disk by pressing `ZQ`.

### Repeat Insert
* Everyone knows that you can insert a character repeatedly using a command such as `20i-` - which will insert 20 '-'. Or you could do something like `10aHello World Of Vim.`. This will do 10 appends of the phrase 'Hello World Of Vim'

### On the fly computations
* You're deeply immersed into writting some cool code for your amazing program. Suddenly you have a hankering for some on the fly computations. You want to ... no, you **need** to calculate 42 multiplied by 42. Well damn. You have to stop your editing, pull up the calculator, do the calculations, copy them, go back to editing, and paste them. PHEW!!!
- Too much work.
- Here's a simpler solution. While in Insert mode press `=`. You will see an equal sign appearing in the bottom of the window. Enter your math formula - eg: `42*42` and press enter. The result will be magically inserted before cursor while still keeping you in insert mode. (the result is 1764 if you were curious).
- Note of warning, certain operations such as `2^10` or `2**10` which you would expect to raise 2 to power of 10 don't work in that syntax. You'll have to use function instead, the `pow(2,10)` will raise 2 to power of 10.
- You can see more info by checking the help `:h expression`

### History of past searches
* You search for various keywords in your code. After a while you want to search for some of those keywords again but you don't remember them exactly. No worries. Just press `q/` and you'll open a small window at the bottom containing your searches. Navigate with `jk` and press (Enter) to repeat the selected search. Or just close that window with `:q`

### Useful selection of g commands
* `gf` open file under cursor
* `g;`traverse forward through the change list (for example after you edit in Insert mode)
* `g,`traverse backward through the change list
* `gi` go back to last insert position and enter insert mode, from wherever you are
* `gf` go to file under cursor (or select the whole line with `` if the path has spaces
* `ga` - show char codes for char under cursor
* `g&` repeat last `:s` on all lines (last replace command)
* `gv` repeat last visual selection.

### Paste word under cursor
* You're in command mode, trying to write a complex search & replace command. You want to search for the word "Supercalifragilisticexpialidocious" and replace it with "Super". Your fingers go on strike before you even start. What to do?. Well, assuming your cursor is on the said word you can paste that word in mode by typing ``. This will paste the word under the cursor.
- this is also useful when you have words with tricky spelling.

### Create and use abbreviation.
* You're documenting your code. It's a mess. You need to use separators to make things clearer. You decide to use a long string, like `#--------------------------------------------------`. Typing it every time it's cumbersome and you will probably not get the amount of dashes right every time.
What to do?
You could yank it in a register and paste it. But I think there's another, more flexible way.
You use abbreviations. Type:

`iab sep #-----------------------------------------------`

now in Insert mode type `sep` and press `Tab`. Your long separator is inserted. By using `:iab` you only create abbreviations for Insert mode and keep the other modes clean.

- HINT - to clear abbreviations type `:abc`

### List words under cursor.
* You're hard at work debugging your code. You left clues in form of comments containing the word "debug" - eg "#debug this or you'll get fired". You're somewher in the middle of the file but how many more lines containing the word "debug" are there?
- with the cursor over the word "debug" (or any other word) from Normal mode type `]I`. A list will appear at the bottom containing all lines containing the word under cursor, starting from the current line position. If you want the search to start from the beginning of the file (instead of curent line) type `[I`
- you can use this cool function for quickly displaying lines containing error codes, certain strings, etc.

### Pattern searching tricks
* `/debug/1` - goes to the line below the line containing the pattern "debug". use another number for a negative offset or a larger offset. eg: `/debug/-4` - 4 lines above the line containing the debug pattern.
* `/debug/e+1` - go to +1 char after the end of pattern "debug". eg: "debug3" will put the cursor on "3"
* `/debug/b+3` - go to +3 chars after the beginning of pattern debug. In this case the cursor will be on "u" (not 'b' because counting starts at 0, where 0 char is the first char, in this case 'd')
* If later you decide you need another offset use `//e+10` - where 'e+10' is your new offset but using the old seach pattern.

### Use expression register to store and iterate
* You have a piece of code with the following word repeated 10 times: `var a1=42`. You want to have `var a1=42`, `var a2=42`, etc until `var a10=42`. How could you do that? By hand? NOOO.
* First set a variable to 0. `:let i=0`
* Now start to record a macro `qa` (record in register "a")
* Find your desired value using `/\va1/e`. The `/e` tells vim to place the cursor at the end of the patter, in this case on the digit `1`. Note that we're using `/\v` to signal vim to use 'very magic' (which means we don't have to escape certain special chars)
* Now for the magic. Start by incrementing the variable i. `:let i += 1` (spaces are important)
* press `s` to enter insert mode and delete the digit `1` at the same time.
* And now insert the value of `i` using the expression register. `=i` (which will just echo the value of i and place it at cursor)
* Stop recording with `q`
* Apply the macro to all lines using `% norm @a` (on all lines eecute macro stored in 'a' register)
* DONE.

### Save and load your sessions.
* You are immersed into a highly complex editing session. You have log files, scripts, documentation and other files, all open in windows and tabs. Suddenly there's a computer crash. You open vim again but now you have to re-open all those files by hand (and place them in their various locations and windows). That sucks.
* Instead you can simply save your session. Type `:mks mysession` (where myssesion is your session file) to save your session to a file. Next time you boot up vim use `vim -S mysession` to load your session.
* Or do it directly from vim. `:so mysession`

### Go back in history.
* You edit a bunch of files. After a couple of months you need to change them again. Trouble is, you don't remember exactly what files you edited.
* Type `:ol` and vim will show you your history (of file edits).
* To open one of these files type `:bro :ol` and choose a number coresponding to the desired file.

### Go back to the line you last edited
* You start editing a file. Suddenly the phone calls. Your cat has won the lottery. After you collect the prize and buy the cat some toys you come back. You want to resume your work but you don't remember the exact line you were in. The file name it's also vague. What do you do?
* You type "`0" (backtick followed by zero). Vim will open the last edited file on the exact line you left it.

### Terminal inside vim
* You have 2 scripts and a config file open in separate windows. It's all good. But you need to run some quick commands in the terminal. Oh no. You don't want to leave the warm bossom of Vim. What to do?
* You could press `` and put Vim in background (which will open a terminal). Then you could type `fg` in terminal to get back to vim.
* Or you could type `:sh` to open a shell temporarily and hide vim. When you're done you could press `exit` and get back to vim.
* But all these options aren't exactly what you want. You want the terminal, true, but you also need to view and edit your files **at the same time**.
* You type `:ter` and a terminal opens alongside your open windows. Yay! When you're done just type `exit` in the terminal.

### Persistent undo
* Wouldn't it be cool to be able to undo your changes **after** you reopen your file? In vim this is quite easy to do.
* Start by creating a dir where you want your undo info to go. Here's a good choice `~/.vim/undo-dir`
* Add the following two lines to your `.vimrc` (located usually at `~/.vimrc`:
```
set undodir=~/.vim/undo-dir
set undofile
```

### Load the previous command
* You type a complex command. Later you want that command again. One option would be to use the arrow keys and cycle through history. That works but takes your hands from the home row position.
* Another way to load last command is `::`. That is: start by tyying colon, press Ctrl+R and type colon again. Colon is a register storing your last command. Ctrl+R outputs the contetns of a register.

### Append your registers.
* You open two important documents. From one you start yanking important lines in a register. You go to the second document and paste but realize you missed a couple of lines. Damn. Now you have to yank all the lines and the ones you missed.
* Or do you? Instead you can just append to the register in which you yanked. Simply yank in the uppercase version of the register and you will append (eg: if you yanked in `a` now you append by yanking in `A`

### Range shortcut
* Press `5:` and vim will type for you in the command line `:.,.+4`

### Visual Block Syntax
* If you've used Vim for a while you know you can edit multiple lines at a time. Use Visual Block ``, use a motion `3j`, insert some text `IHelloWorld` and press ``. BAM! Your inserted text is typed on all lines.
* But here's the real trick which few people know. Let's say that your vertical line spans some short lines. Eg:
```
I'm a long line, very vory long, YEAH.
Shory.
I'm a long line, very vory long, YEAH.
```
* You start the visual block let' say on the word 'YEAH' and it spans the whole 3 lines. If you use `I` and insert text the short line will remain empty (where it was empty space it'll still be empty space). But if you use `A` (append) then you'll also type text in the empty line. Pretty neat, eh?
* In order to remember think that `A` Append always writes text.

### Quickly run an external command
* It's cool to be able to run external terminal commands with `:%!sort` which passes all lines to sort and writes back the output. But there's a neat trick that will save you some time:
* `!5G` - will start writting an command that looks like `:.,+4!`. You then will type your desired program `sort` and press enter. You start with `!` and then specify a motion from the current line `5G`. You can use other ranges, like `!4j` which will sort the following 4 lines from your current line.
* An even faster shortcut is `!!`. This will pass the current line to the external program (and replace it with the output). A known use case of this is to quickly insert a timestamp into your document `!!date`

### Replace with confirmation
* You have document. In it you have a variable called "money". You want to rename it to "cash" but only for certain cases. In that case you should type: `:%s/\v/cash/gc`. This long winded command uses very magic `\v` so that you won't have to escape `<>`. Those chars mark the beginning and end of a word. We use them because you presumably want to replace only the instance of "money" and not "zamoney" or "moneys". Finally the `c` flag will prompt a confirmaton dialogue each time an entry is found.
* HINT - use `` and `` to scroll up and down so you can better see the context during the replace confirm dialogue.

### Documentation at your fingertips
* You're editing a bash file. You read the output from `find` and for each result you want to run an external script. You decide to use `xargs` instead of `-exec {} \;`. But as you write your command you find that you're rusty on xargs arguments. What to do?
* You could put vim in foreground ``, `man xargs`, `fg`. Or you could open a terminal inside vim with `:ter`, check the docs then close the window with ``.
* But there are 2 better ways to do this.
* Just press `K` (Shift+k) on the keyword you're interested in and Vim will open the relevant man page. If it's another type of file (not bash) vim will also try to find the help for that particular keyword. For example you could put your cursor on `pow()` in a python file, type `K` and vim will show you the docs. Pretty cool, eh? One keystroke and the docs are open! AWESOME!
* But there's more. There is a filetype plugin which gives you an enhanced version of man. First install it with `:runtime! ftplugin/man.vim` (put it in your .vimrc if you want it open at startup).
* Now type `:Man xargs`. Vim will open the manual page inside vim in a separate window. That's cool and it save you the hassle of opening a terminal by hand and typing man inside it.
* That's cool but it's just half of the gooodness. The other half is this. Inside this man window put your curosr on a keyword. Now press either `\K` (backward slash followed by Shift+k) or ``. If there exists a man for that keyword it will open inside the same page. Like a browser. THis functionality is NOT present in the default man pages. You can navigate back and forth with ``, ``
* And for a last tip - you can use `\K` inside vim too on a keyword. Then vim will open the new and improved man page instead of the default documentation (whith opens with `K`)
* BUT NOTE! the `:Man` command works only for man pages for linux, not other programming languages. That is if you press `\K` on 'pow' inside a python file you will get the man page for 'POW(3)' (linux programmer manual) and not python.

### Input/output with external commands.
1. `:!date` - execute date command and print the results
2. `:r !date` - execute date command and append the output after range last line. If no range provided use current line. Thus the results from date will be appended after the current line in our case.
3. `:w !date` - send all the lines as stdin to date command. Print the results (no insertion into current buffer)
4. `:1,3!date` send lines 1 to 3 as stdin to date command. Replace the lines in range (1,3) with output from date.

### Put each word on a new line
* Put all words from a line on a new line. eg: "hello world of vim" will be: "hello\n world\n of\n vim\n". How? With `:.!xargs -n1`. It says: send current line as stdin to xargs. You, xargs, split the line into args separated by blank space and `echo` at most one word. Then put the xargs output in place of the line. Since the output from xargs contains newlines this creates extra lines.
* You could also use a range, to put each word on the lines in range on a new line with `:1,5!xargs -n1`
* NOTE - xargs separates words by spaces. Vim has a default different way of separating words which may or may not corespond with xargs. (see `:h isk`

### Buffer delete
* As you know buffers are usually contents of files loaded in memory, with extra info attached to them (marks, registers, etc).
* Let's say you decide to delete some buffers with `:bdel myverylongfile`. 5 minutes later you need again the buffer you deleted. Darn. What to do? You could try and remember the filename and reopen it. But what if there were lots of buffers you deleted and they havo complicated names?
* Vim it's here to help you. Just type `:ls!` to show all buffers, even [u]nlisted ones. You'll see your deleted buffer listed (they'll have a 'u' indicator in front of them for unlisted). Turns out deleting a buffer makes it unlisted.
* If you really, really want to delete a buffer use `:bwipe`.

### Autocomplete with files/lines
* You're editing a file. You have separator comments for sections, like `#DEBUG---------------------`. At some time you would like to insert that line into your current text. You could use a register but what if you have lots of types of separator comments (DEBUG, WIP, STABLE,etc)? Here's a better way:
* Type `` (Ctrl+x, Crl+l). The autocomplete will show you whole lines and you can choose your separator comment line. (in Insert mode)
* will show you autocomplete options from the files in current directory. Quite cool. (in Insert mode)
* After the autocomplete list appears you can cycle through it with `` or ``.
* But here's an even crazier thingie - you can start typing an existing path and Vim will try and autocomplete it. Eg: you have typed `/` and are still in Insert mode. Type `,` and a list of dirs under root dir will appear. Cycle through them with `` or ``. If you want to go deeper you can't press Space because that will just enter that dir/file and a space afterwards. INstead press `,` and you will have inserted that dir/file name and will go one level deeper (to the next forward slash) where you can cycle through the next options.
* You can use the above feature in combination with `gf` or `f` to open the files under cursor in vim. Very flexible.

### Repeat your insert
* You start editing a file. You type rather long text containing a copyright comment. You enter Normal mode, you jump to the end of the file and see that you will have to enter the same line again (for some reason).
* Enter insert mode and press `` - it'll insert the text you previously typed in Insert mode.

### Better wrap
* After you set up the wrap option `:se wrap` you notice that words may be cut of in the middle at end of screen. Like so:
```
hello wo
rld of v
im
```
* Use `:se linebreak` and have the words not cut of in the middle:
```
hello
world of
vim
```

### Indent in Insert mode
* You're probably using the indent operators in Normal mode (to shift your lines to the rigt/left an amount of space). `>>` and `<<` will shift left/right a line. `>` works with other motion and text objects: `>ap`, `>3j`, etc. (`gg>G` will shift right all lines in a file)
* But if you're in Insert mode it can be a pain to switch to Normal and back again.
* It turns out you don't have to. You can use `` and `` to shift left/right right from Insert mode.

### Smart folding
* Folding is great. Trouble is - it sucks doing it by hand. Wouldn't it be great of Vim automatically created folds based on the indent level? That would work nicely for most programming languages.
* `:se foldmethod=indent` (instead of manual) and vim will automaticall fold based on 'shiftwidth' indents (if you change this setting in the middle of editing folding won't behave as expected)
* Now use the usual shortcuts to manipulate folds (`,,,,etc`)

### Increment numbers
* You're editing a file where you have years as dates. eg: "in 1825 the world...after 1841 something...". You receive a call from your editor/boss and he tells you that the dates are wrong. All years should be modified by adding 153 years to them.
* Damn. You're in no mood for mental math juggle. And you have lots of years. What to do?
* Put your cursor over a year. Type `153` (153 followed by Ctrl+a). Magically the year will be incremented by 153. Pretty cool. But you don't want to do this for all the years - you have hundreds of such dates.
* Use a macro. `ggqa`. Go to top of file, start recording. `/\<\d\d\d\d\>` and press Enter (to find years). `153` (153 followed by Ctrl+a). `q` to stop recording. `:%norm @a` to apply this macro to all lines.

### Copy a protected file and edit it immediately.
* You need to take a look and modify the dmesg file. Trouble is you can't if you started vim as a regular user - dmesg is owned by root. You could exit vim, make a copy, come back and re-open.
* Here's a one liner that will save you the hassle: `:exec '!cp /var/log/dmesg .' | e dmesg`. First it executes the copy command. The pipe operator (vertical bar) chains commands in vim mode. Immediately after a edit command is issued.

### Comment a whole file (or a portion)
* You open a long python script. You run it but you get errors. Darn. You decide to debug it by commenting it completely and uncomment sections as you see fit.
* Commeting by hand it's troublesome - there are 1520 lines. You could try some fancy stuff with a Visual Block and insert but that might not be the best way.
* Instead you do `:%norm i#`. Kaboom - your whole script is commented out. Not smartly mind you (existing comments will be double commented) but it works nicely for your purposes. You can do the same for a .c file (or another file that supports these types of comments) with `:%norm i//`. You tell vim to execute a normal command across all lines (go to first char in line, even if it's empty and insert a comment)
* If you want to comment a section just use range `:1,50norm i#`. If you have a visual selection and you type the colon you'll be presented with `:'<,'>` which means a range between the start and the end of the visual selection. Then you just type `norm i#` after the already present command.
* Using the same logic you could append semicolons to all lines in a file (or a range). Check it out: `%norm A;` - on all lines execute normal command A (which appends after the last char) and type a semicolon.

### Keep temp commands in registers
* You have a particularly useful command which you use repeatedly. It is: `:-1,+1norm i#` - it comments out the current line, the line above and the line below. As you work you want to execute this command, now an then. But you don't like typing it out every time.
* So instead you type the command in the text, just without the semicolon, on a new line:
```
#bla bla
-1,+1norm i#
```
* Put your cursor on the line where the command is and delete it in a register, say 'w'. `"wdd` (in register w store this line and delete it from text)
* Now your register has your command. But how to run it?
* Easy. Type `:@w` - where 'w' is your register. Press enter and you'll execute this command.
* Here's the explanation. When typing commands a `@` sign in front of a letter signifies a register. the `@w` signifies the `w` register. When you type this special variable in command window it just reads the contents of this register and executes it (after you press Enter).
* Fun fact. You can repeat your last command with `:@:`. The register `:` stores the last command. `@:` is used to signify this register while entering a command (and pressing Enter afterwards so that the command executes)

### Open extra files with terminal commands like find
* When you open vim with some files as arguments they are stored in `:args`. args are different from buffers. Buffers are all the buffers opened in memory and not necesarilly files. Args are the actual file args passed at startup. If you change the args the buffers stay untouched and viceversa.
* Think about `:args` as a temporary list of files which you can modify to your desire. You navigate files in args with `:next` and `:prev` (whereas you navigate buffers with `:bn` `:bp` `:bf` `:bl`).
* After you load vim and start editing some file you realize you have to also view some log files. What to do?
* One possible way is to create a new buffer with `:new`. Afterwards put into this buffer all the results from find with `:r !find /var/log -size +1M`. All the results will be placed in the new buffer, each file path on a new line. Just press `gf` on a line and vim will open the file in a new window (and buffer). That's one approach.
* Another is to just run
```
:args `find /var/log -size +1M -name '*.py' \|\| true`
```
(OR)
```
:args `find /var/log -size +1M -name '*.py' \| xargs -n1`
```
* Now if you type `:args` you'll see it is populated by all the results from find. Now you can naviate quickly throug these files.
* Each method has drawbacks. Using this last approach you load all the results at once but the command is more tricky to type and your buffers may be overloaded. Using the first approach on the other hand will require you to go back to that new buffer and `gf` on each file you want opened. Choose what suits you best.
* For more see `:h backtick-expansion`

### Format with care
* You probably now about formatting with `gq`. You do things like `gggqG` to forma the whole file.
* But `gq` will also move the cursor to the motion end range (eg; end of file). In order to format but keep the cursor where it is you use `gw` - just in the same way. Like `gggwG`.

###

### patterns
* You're editing some source code left to you by your predecesor. It's messy. That fellow used to abbreviate troublesome variables with 'dbg_', like 'dbg_count', 'dbg_class', etc. Just how many of these variables are there?
* You can search for them with the substitute command. Shocking, I know. Check it out: `:%s/