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This repository was archived by the owner on Jun 5, 2024. It is now read-only.

Commit 018c8f0

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formatting changes, improved fixed string matching section
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‎ruby_one_liners.md

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@@ -84,7 +84,7 @@ DESCRIPTION
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**Prerequisites and notes**
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* familiarity with programming concepts like variables, printing, control structures, arrays, etc
87-
* familiarity with regular expression
87+
* familiarity with regular expressions
8888
* this tutorial is primarily focussed on short programs that are easily usable from command line, similar to using `grep`, `sed`, `awk`, `perl` etc
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* unless otherwise specified, consider input as ASCII encoded text only
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* this is an attempt to translate [Perl chapter](./perl_the_swiss_knife.md) to `ruby`, I don't have prior experience of using `ruby`
@@ -197,8 +197,8 @@ I bought two bananas and three mangoes
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**Further Reading**
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200-
* [ruby-doc Pre-defined variables](https://ruby-doc.org/core-2.5.0/doc/globals_rdoc.html#label-Pre-defined+variables) for explanation on `$_` and other such special variables
201-
* [ruby-doc gsub](https://ruby-doc.org/core-2.5.0/String.html#method-i-gsub) for `gsub` syntax details
200+
* [ruby-doc: Pre-defined variables](https://ruby-doc.org/core-2.5.0/doc/globals_rdoc.html#label-Pre-defined+variables) for explanation on `$_` and other such special variables
201+
* [ruby-doc: gsub](https://ruby-doc.org/core-2.5.0/String.html#method-i-gsub) for `gsub` syntax details
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<br>
204204

@@ -209,9 +209,9 @@ I bought two bananas and three mangoes
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#### <a name="regular-expressions-based-filtering"></a>Regular expressions based filtering
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211211
* one way is to use `variable =~ /REGEXP/FLAGS` to check for a match
212-
* `variable !~ /REGEXP/FLAGS` for negated match
212+
* use `variable !~ /REGEXP/FLAGS` for negated match
213213
* by default acts on `$_` if variable is not specified
214-
* see [ruby-doc Regexp](https://ruby-doc.org/core-2.5.0/Regexp.html) for regular expression details
214+
* see [ruby-doc: Regexp](https://ruby-doc.org/core-2.5.0/Regexp.html) for regular expression details
215215
* as we need to print only selective lines, use `-n` option
216216
* by default, contents of `$_` will be printed if no argument is passed to `print`
217217

@@ -244,7 +244,7 @@ Violets are blue,
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```
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* using different delimiter
247-
* quoting from [ruby-doc Percent Strings](https://ruby-doc.org/core-2.5.0/doc/syntax/literals_rdoc.html#label-Percent+Strings)
247+
* quoting from [ruby-doc: Percent Strings](https://ruby-doc.org/core-2.5.0/doc/syntax/literals_rdoc.html#label-Percent+Strings)
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249249
> If you are using "(", "[", "{", "<" you must close it with ")", "]", "}", ">" respectively. You may use most other non-alphanumeric characters for percent string delimiters such as "%", "|", "^", etc.
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@@ -272,73 +272,62 @@ $ ruby -ne 'print if !%r#/foo/a/#' paths.txt
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#### <a name="fixed-string-matching"></a>Fixed string matching
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275-
* To match strings literally, use `index`
276-
* See [ruby-doc index](https://ruby-doc.org/core-2.5.0/String.html#method-i-index) for details
275+
* To match strings literally, use `include?` method
277276

278277
```bash
279-
$ # index returns matching position(starts at 0) and nil if not found
280-
$ # same as: perl -ne 'print if index($_, "a[5]") != -1'
281278
$ echo 'int a[5]' | ruby -ne 'print if /a[5]/'
282-
$ echo 'int a[5]' | ruby -ne 'print if $_.index("a[5]")'
279+
$ echo 'int a[5]' | ruby -ne 'print if $_.include?("a[5]")'
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int a[5]
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285-
$ # however, string within double quotes gets interpolated, for ex
286-
$ ruby -e 'a=5; puts "value of a: #{a}"'
287-
value of a: 5
288-
289-
$ # so, for commandline usage, better to pass string as environment variable
290-
$ # they are accessible via the ENV hash variable
291-
$ # same as: perl -le 'print $ENV{SHELL}'
292-
$ ruby -e 'puts ENV["SHELL"]'
293-
/bin/bash
294-
295-
$ echo 'int #{a}' | ruby -ne 'print if $_.index("#{a}")'
296-
-e:1:in `<main>': undefined local variable or method `a' for main:Object (NameError)
297-
$ echo 'int #{a}' | s='#{a}' ruby -ne 'print if $_.index(ENV["s"])'
282+
$ # however, string within double quotes gets interpolated
283+
$ ruby -e 'a=5; puts "value of a:\t#{a}"'
284+
value of a: 5
285+
$ # use %q (covered later) to specify single quoted string
286+
$ echo 'int #{a}' | ruby -ne 'print if $_.include?(%q/#{a}/)'
287+
int #{a}
288+
$ # or pass the string as environment variable
289+
$ echo 'int #{a}' | s='#{a}' ruby -ne 'print if $_.include?(ENV["s"])'
298290
int #{a}
299291
```
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301-
* `index` allows to use regex as well
293+
* restricting match to start/end of line
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```bash
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$ # passing string
305-
$ ruby -ne 'print if $_.index("a+b")' eqns.txt
296+
$ cat eqns.txt
297+
a=b,a-b=c,c*d
306298
a+b,pi=3.14,5e12
307299
i*(t+9-g)/8,4-a+b
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309-
$ # passing regex
310-
$ ruby -ne 'print if $_.index(/a+b/)' eqns.txt
311-
$ ruby -ne 'print if $_.index(/a\+b/)' eqns.txt
301+
$ # start of line
302+
$ s='a+b' ruby -ne 'print if $_.start_with?(ENV["s"])' eqns.txt
312303
a+b,pi=3.14,5e12
304+
305+
$ # end of line
306+
$ # -l option is needed to remove record separator (covered later)
307+
$ s='a+b' ruby -lne 'print if $_.end_with?(ENV["s"])' eqns.txt
313308
i*(t+9-g)/8,4-a+b
314309
```
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316-
* return value is useful to match at specific position
317-
* for ex: at start/end of line
311+
* `index` method returns matching position (starts at 0) and nil if not found
312+
* supports both string and regex
313+
* optional 2nd argument allows to specify offset to start searching
314+
* See [ruby-doc: index](https://ruby-doc.org/core-2.5.0/String.html#method-i-index) for details
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```bash
320-
$ cat eqns.txt
321-
a=b,a-b=c,c*d
317+
$ # passing string
318+
$ ruby -ne 'print if $_.index("a+b")' eqns.txt
322319
a+b,pi=3.14,5e12
323320
i*(t+9-g)/8,4-a+b
324-
325-
$ # start of line
326-
$ # same as: s='a+b' perl -ne 'print if index($_, $ENV{s})==0' eqns.txt
327-
$ s='a+b' ruby -ne 'print if $_.index(ENV["s"])==0' eqns.txt
321+
$ ruby -ne 'print if $_.index("a+b")==0' eqns.txt
328322
a+b,pi=3.14,5e12
329323

330-
$ # optional 2nd argument allows to specify offset to start searching
331-
$ # similar to: s='a+b' perl -ne 'print if index($_, $ENV{s})>0' eqns.txt
332-
$ s='a+b' ruby -ne 'print if $_.index(ENV["s"], 1)' eqns.txt
324+
$ # passing regex
325+
$ ruby -ne 'print if $_.index(/[+*]/)<5' eqns.txt
326+
a+b,pi=3.14,5e12
333327
i*(t+9-g)/8,4-a+b
334328

335-
$ # end of line
336-
$ # same as: s='a+b' perl -ne '$pos = length() - length($ENV{s}) - 1;
337-
$ # print if index($_, $ENV{s}) == $pos' eqns.txt
338-
$ s='a+b' ruby -ne 'pos = $_.length - ENV["s"].length - 1;
339-
print if $_.index(ENV["s"]) == pos' eqns.txt
329+
$ s='a+b' ruby -ne 'print if $_.index(ENV["s"], 1)' eqns.txt
340330
i*(t+9-g)/8,4-a+b
341-
$ # .size can also be used instead of .length
342331
```
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344333
<br>
@@ -347,7 +336,7 @@ $ # .size can also be used instead of .length
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348337
* special variable `$.` contains total records read so far, similar to `NR` in `awk`
349338
* as far as I've checked the docs, there's no equivalent of awk's `FNR`
350-
* See also [ruby-doc eof](https://ruby-doc.org/core-2.5.0/IO.html#method-i-eof)
339+
* See also [ruby-doc: eof](https://ruby-doc.org/core-2.5.0/IO.html#method-i-eof)
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```bash
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$ # print 2nd line
@@ -370,7 +359,7 @@ And so are you.
370359
```
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* for large input, use `exit` to avoid unnecessary record processing
373-
* See [ruby-doc Control Expressions](https://ruby-doc.org/core-2.5.0/doc/syntax/control_expressions_rdoc.html) for syntax details
362+
* See [ruby-doc: Control Expressions](https://ruby-doc.org/core-2.5.0/doc/syntax/control_expressions_rdoc.html) for syntax details
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375364
```bash
376365
$ # same as: perl -ne 'if($.==234){print; exit}'
@@ -394,7 +383,7 @@ $ seq 14 25 | ruby -pe 'exit if $.==3'
394383
```
395384

396385
* selecting range of lines
397-
* See [ruby-doc Range](https://ruby-doc.org/core-2.5.0/Range.html) for syntax details
386+
* See [ruby-doc: Range](https://ruby-doc.org/core-2.5.0/Range.html) for syntax details
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```bash
400389
$ # in this context, the range is compared against $.
@@ -472,7 +461,7 @@ $ printf ' a ate b\tc \n' | ruby -ane 'puts $F.length'
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473462
* operators `=`, `!=`, `<`, etc will work for both string/numeric comparison
474463
* unlike `perl`, numeric comparison for text requires converting to appropriate numeric format
475-
* See [ruby-doc string methods](https://ruby-doc.org/core-2.5.0/String.html#method-i-to_c) for details
464+
* See [ruby-doc: string methods](https://ruby-doc.org/core-2.5.0/String.html#method-i-to_c) for details
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```bash
478467
$ # if first field exactly matches the string 'apple'
@@ -563,7 +552,7 @@ baz
563552
```
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* to process individual characters, simply use indexing on input string
566-
* See [ruby-doc Encoding](https://ruby-doc.org/core-2.5.0/Encoding.html) for details on handling different string encodings
555+
* See [ruby-doc: Encoding](https://ruby-doc.org/core-2.5.0/Encoding.html) for details on handling different string encodings
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568557
```bash
569558
$ # same as: perl -F -lane 'print $F[0]'
@@ -850,7 +839,7 @@ $ seq 6 | ruby -lpe '$\ = $.%3!=0 ? "-" : "\n"'
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851840
* Processing consecutive lines
852841
* to keep the one-liner short, global variables(`$` prefix) are used here
853-
* See [ruby-doc Global variables](https://ruby-doc.org/core-2.5.0/doc/syntax/assignment_rdoc.html#label-Global+Variables) for syntax details
842+
* See [ruby-doc: Global variables](https://ruby-doc.org/core-2.5.0/doc/syntax/assignment_rdoc.html#label-Global+Variables) for syntax details
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855844
```bash
856845
$ cat poem.txt
@@ -934,9 +923,10 @@ a
934923

935924
## <a name="ruby-regular-expressions"></a>Ruby regular expressions
936925

937-
* assuming that you are already familiar with basic [ERE features](./gnu_sed.md#regular-expressions)
926+
* assuming that you are already familiar with basics of regular expressions
927+
* if not, see [Ruby Regular Expressions tutorial](https://github.com/learnbyexample/Ruby_Scripting/blob/master/chapters/Regular_expressions.md)
938928
* examples/descriptions based only on ASCII encoding
939-
* See [ruby-doc Regexp](https://ruby-doc.org/core-2.5.0/Regexp.html) for syntax and feature details
929+
* See [ruby-doc: Regexp](https://ruby-doc.org/core-2.5.0/Regexp.html) for syntax and feature details
940930
* See [rexegg ruby](https://www.rexegg.com/regex-ruby.html) for a bit of ruby regex history and differences with other regex engines
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942932
<br>
@@ -1021,7 +1011,7 @@ $ # without newline at end of line, both \z and \Z will give same result
10211011
```
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10231013
* delimiters and quoting
1024-
* from [ruby-doc Percent Strings](https://ruby-doc.org/core-2.5.0/doc/syntax/literals_rdoc.html#label-Percent+Strings)
1014+
* from [ruby-doc: Percent Strings](https://ruby-doc.org/core-2.5.0/doc/syntax/literals_rdoc.html#label-Percent+Strings)
10251015

10261016
> If you are using "(", "[", "{", "<" you must close it with ")", "]", "}", ">" respectively. You may use most other non-alphanumeric characters for percent string delimiters such as "%", "|", "^", etc.
10271017
@@ -1126,7 +1116,7 @@ $ echo '123:42:789:good:5:bad' | ruby -pe 'sub(/:.*:[a-z]/, ":")'
11261116
The string matched by lookarounds are like word boundaries and anchors, do not constitute as part of matched string. They are termed as **zero-width patterns**
11271117

11281118
* positive lookbehind `(?<=`
1129-
* See also [ruby-doc scan](https://ruby-doc.org/core-2.5.0/String.html#method-i-scan)
1119+
* See also [ruby-doc: scan](https://ruby-doc.org/core-2.5.0/String.html#method-i-scan)
11301120

11311121
```bash
11321122
$ s='foo=5, bar=3; x=83, y=120'
@@ -1330,7 +1320,7 @@ He he he
13301320
13311321
* block form allows to use `ruby` code for replacement section
13321322
1333-
quoting from [ruby-doc gsub](https://ruby-doc.org/core-2.5.0/String.html#method-i-gsub)
1323+
quoting from [ruby-doc: gsub](https://ruby-doc.org/core-2.5.0/String.html#method-i-gsub)
13341324
13351325
>In the block form, the current match string is passed in as a parameter, and variables such as 1ドル, 2ドル, $`, $&, and $' will be set appropriately. The value returned by the block will be substituted for the match on each call.
13361326
@@ -1390,7 +1380,7 @@ x:y:z-a-v-xc-gf
13901380
#### <a name="quoting-metacharacters"></a>Quoting metacharacters
13911381
13921382
* to match contents of string variable exactly, all metacharacters need to be escaped
1393-
* See [ruby-doc Regexp.escape](https://ruby-doc.org/core-2.5.0/Regexp.html#method-c-escape) for syntax details
1383+
* See [ruby-doc: Regexp.escape](https://ruby-doc.org/core-2.5.0/Regexp.html#method-c-escape) for syntax details
13941384
13951385
```bash
13961386
$ cat eqns.txt
@@ -1456,7 +1446,7 @@ White
14561446
14571447
* `-r` command line option allows to specify library required
14581448
* the `include?` method allows to check if `set` already contains the element
1459-
* See [ruby-doc include?(o)](https://ruby-doc.org/stdlib-2.5.0/libdoc/set/rdoc/Set.html#method-i-include-3F) for syntax details
1449+
* See [ruby-doc: include?](https://ruby-doc.org/stdlib-2.5.0/libdoc/set/rdoc/Set.html#method-i-include-3F) for syntax details
14601450
14611451
```bash
14621452
$ # common lines
@@ -1482,10 +1472,10 @@ $ # alternate: ARGV.length==1 ? s.add($_) : s.include?($_) && print
14821472
14831473
alternate solution by using set operations available for arrays
14841474
1485-
* [ruby-doc ARGF](https://ruby-doc.org/core-2.5.0/ARGF.html) filehandle allows to read from filename arguments supplied to script
1475+
* [ruby-doc: ARGF](https://ruby-doc.org/core-2.5.0/ARGF.html) filehandle allows to read from filename arguments supplied to script
14861476
* if filename arguments are not present, it would act upon stdin
14871477
* `STDIN` filehandle allows to read from stdin
1488-
* [ruby-doc readlines](https://ruby-doc.org/core-2.5.0/IO.html#method-c-readlines) method allows to read all the lines as an array
1478+
* [ruby-doc: readlines](https://ruby-doc.org/core-2.5.0/IO.html#method-c-readlines) method allows to read all the lines as an array
14891479
* if filehandle is not specified, default is ARGF
14901480
* some comparison notes
14911481
* both files will get saved as array in memory here, while previous solution would save only first file
@@ -1613,15 +1603,15 @@ $ # ruby -e 'STDIN.readlines.zip(readlines).each {|a| puts a[1] if a[0].to_i>0}'
16131603
16141604
For syntax and implementation details, see
16151605
1616-
* [ruby-doc ARGF](https://ruby-doc.org/core-2.5.0/ARGF.html)
1617-
* [ruby-doc times](https://ruby-doc.org/core-2.5.0/Integer.html#method-i-times)
1618-
* [ruby-doc gets](https://ruby-doc.org/core-2.5.0/IO.html#method-i-gets)
1606+
* [ruby-doc: ARGF](https://ruby-doc.org/core-2.5.0/ARGF.html)
1607+
* [ruby-doc: times](https://ruby-doc.org/core-2.5.0/Integer.html#method-i-times)
1608+
* [ruby-doc: gets](https://ruby-doc.org/core-2.5.0/IO.html#method-i-gets)
16191609
16201610
<br>
16211611
16221612
## <a name="creating-new-fields"></a>Creating new fields
16231613
1624-
* See [ruby-doc slice](https://ruby-doc.org/core-2.5.0/Array.html#method-i-slice) for syntax details
1614+
* See [ruby-doc: slice](https://ruby-doc.org/core-2.5.0/Array.html#method-i-slice) for syntax details
16251615
16261616
```bash
16271617
$ s='foo,bar,123,baz'
@@ -1639,7 +1629,7 @@ foo,bar,123,baz,,,42
16391629
```
16401630
16411631
* adding a field based on existing fields
1642-
* See [ruby-doc Percent Strings](https://ruby-doc.org/core-2.5.0/doc/syntax/literals_rdoc.html#label-Percent+Strings) for details on `%w`
1632+
* See [ruby-doc: Percent Strings](https://ruby-doc.org/core-2.5.0/doc/syntax/literals_rdoc.html#label-Percent+Strings) for details on `%w`
16431633
16441634
```bash
16451635
$ # adding a new 'Grade' field
@@ -1706,7 +1696,7 @@ colors_2.txt
17061696
* `-r` command line option allows to specify library required
17071697
* here, `set` data type is used to keep track of unique values - be it whole line or a particular field
17081698
* the `add?` method will add element to `set` and returns `nil` if element already exists
1709-
* See [ruby-doc add?(o)](https://ruby-doc.org/stdlib-2.5.0/libdoc/set/rdoc/Set.html#method-i-add-3F) for syntax details
1699+
* See [ruby-doc: add?](https://ruby-doc.org/stdlib-2.5.0/libdoc/set/rdoc/Set.html#method-i-add-3F) for syntax details
17101700
17111701
```bash
17121702
$ cat duplicates.txt
@@ -1800,7 +1790,7 @@ test toy 123
18001790
18011791
#### <a name="using-uniq-method"></a>using uniq method
18021792
1803-
* [ruby-doc uniq](https://ruby-doc.org/core-2.5.0/Array.html#method-i-uniq)
1793+
* [ruby-doc: uniq](https://ruby-doc.org/core-2.5.0/Array.html#method-i-uniq)
18041794
* original order is maintained
18051795
18061796
```bash
@@ -2083,7 +2073,7 @@ $ # on matching beginning/end REGEXPs respectively
20832073
20842074
## <a name="array-operations"></a>Array operations
20852075
2086-
See [ruby-doc Array](https://ruby-doc.org/core-2.5.0/Array.html) for various ways to initialize and methods available
2076+
See [ruby-doc: Array](https://ruby-doc.org/core-2.5.0/Array.html) for various ways to initialize and methods available
20872077
20882078
* initialization
20892079
@@ -2112,7 +2102,7 @@ $ ruby -le 's = %w[foo "baz" "a\nb"]; print s[-1]'
21122102
```
21132103
21142104
* array slices
2115-
* See also [ruby-doc Array to Arguments Conversion](https://ruby-doc.org/core-2.5.0/doc/syntax/calling_methods_rdoc.html#label-Array+to+Arguments+Conversion)
2105+
* See also [ruby-doc: Array to Arguments Conversion](https://ruby-doc.org/core-2.5.0/doc/syntax/calling_methods_rdoc.html#label-Array+to+Arguments+Conversion)
21162106
21172107
```bash
21182108
$ # accessing more than one element in random order
@@ -2204,7 +2194,7 @@ $ echo "$s" | ruby -lane 'print $F.sample(2)'
22042194
22052195
#### <a name="sorting"></a>Sorting
22062196
2207-
* [ruby-doc sort](https://ruby-doc.org/core-2.5.0/Array.html#method-i-sort)
2197+
* [ruby-doc: sort](https://ruby-doc.org/core-2.5.0/Array.html#method-i-sort)
22082198
* See also [stackoverflow What does map(&:name) mean in Ruby?](https://stackoverflow.com/questions/1217088/what-does-mapname-mean-in-ruby) for explanation on `&:`
22092199
22102200
```bash
@@ -2298,7 +2288,7 @@ ECE 92 Om
22982288
CSE 67 Amy
22992289
```
23002290
2301-
* [ruby-doc uniq](https://ruby-doc.org/core-2.5.0/Array.html#method-i-uniq)
2291+
* [ruby-doc: uniq](https://ruby-doc.org/core-2.5.0/Array.html#method-i-uniq)
23022292
* order is preserved
23032293
23042294
```bash
@@ -2406,7 +2396,7 @@ $ echo 'foobar' | ruby -lpe '$_.reverse!'
24062396
raboof
24072397
```
24082398
2409-
* See also [ruby-doc Enumerable](https://ruby-doc.org/core-2.5.0/Enumerable.html) for more methods like `inject`
2399+
* See also [ruby-doc: Enumerable](https://ruby-doc.org/core-2.5.0/Enumerable.html) for more methods like `inject`
24102400
24112401
<br>
24122402
@@ -2418,7 +2408,7 @@ raboof
24182408
24192409
* the `-a` command line option uses `split` and automatically saves the results in `$F` array
24202410
* default separator is `\s+` and also strips whitespace from start/end of string
2421-
* See also [ruby-doc - split](https://ruby-doc.org/core-2.5.0/String.html#method-i-split)
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* See also [ruby-doc: split](https://ruby-doc.org/core-2.5.0/String.html#method-i-split)
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```bash
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$ # specifying maximum number of splits
@@ -2467,7 +2457,7 @@ $ # ruby -F, -ane '$F[1].scan(/[^:]+/) {|x| print [$F[0],x,$F[2]]*","}'
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#### <a name="fixed-width-processing"></a>Fixed width processing
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* [ruby-doc unpack](https://ruby-doc.org/core-2.5.0/String.html#method-i-unpack)
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* [ruby-doc: unpack](https://ruby-doc.org/core-2.5.0/String.html#method-i-unpack)
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```bash
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$ # same as: perl -lne '@x = unpack("a1xa3xa4", $_); print $x[0]'
@@ -2527,7 +2517,7 @@ $ ruby -0777 -ne 'print $_ * 100' poem.txt | wc -c
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#### <a name="transliteration"></a>transliteration
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* [ruby-doc tr](https://ruby-doc.org/core-2.5.0/String.html#method-i-tr)
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* [ruby-doc: tr](https://ruby-doc.org/core-2.5.0/String.html#method-i-tr)
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```bash
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$ echo 'Uryyb Jbeyq' | ruby -pe '$_.tr!("a-zA-Z", "n-za-mN-ZA-M")'
@@ -2580,7 +2570,7 @@ I bought two bananas and three mangoes
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```
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* return value of `system` or global variable `$?` can be used to act upon exit status of command issued
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* see [ruby-doc system](https://ruby-doc.org/core-2.5.0/Kernel.html#method-i-system) for details
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* see [ruby-doc: system](https://ruby-doc.org/core-2.5.0/Kernel.html#method-i-system) for details
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```bash
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$ ruby -e 'es=system("ls poem.txt"); puts es'

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